[PATCH 0/9] Add support for an external command for fetching notes

[PATCH 0/9] Add support for an external command for fetching notes

[Siddh Raman Pant]

Hi,

This series teaches the notes display machinery to obtain note text from a
long-lived external helper configured by `notes.externalCommand`.

The motivation is mentioned in the main commit message (PATCH 7/9).

The helper protocol is intentionally narrow. Git starts the command once,
sends one commit object ID per request, and expects either:

	<object-id> missing
	<object-id> ok <n>
	<n bytes of UTF-8 note text>

with the documented trailing newlines. The command is read only from protected
configuration, so an untrusted repository cannot make ordinary note display run
arbitrary commands. If the helper cannot be started, times out, exits, or sends
an invalid response, Git warns once, disables it for the rest of the process,
and continues without external notes.

Users can control from command line too with `--external-notes` and
`--no-external-notes`. The semantics are close to `--notes=<ref>`:
`--external-notes` implies naming an explicit notes source by itself, while
`--external-notes --notes` combines it with the default notes refs, and
`--external-notes --notes=<ref>` combines it with specific notes refs. The
series also adds `notes.externalCommandName`, `notes.externalCommandTimeoutMs`,
and the opt-in `notes.externalCommandForGrep` knob for installations that want
external notes to participate in `--grep` matching.

Because this puts an external process on the log-formatting path, the series
also adds the small support pieces needed to keep that boundary bounded:
timeout/deadline variants of the read helpers, a timeout-aware command
finisher, and cleanup that escalates if the helper does not exit promptly.

Testing: https://github.com/siddhpant/git/actions/runs/26107938855

Thanks,
Siddh

Siddh Raman Pant (9):
  Documentation/git-range-diff: add missing notes options in synopsis
  notes: convert raw arg in format_display_notes() to bool
  wrapper: add sleep_nanosec
  run-command: add support for timeout in command finisher
  wrapper: add support for timeout and deadline in read helpers
  t3301: cover generic displayed notes behavior
  notes: support an external command to display notes
  Documentation: document external notes command options
  t: add tests for external notes command

 Documentation/config/notes.adoc             |  57 +++
 Documentation/git-format-patch.adoc         |  11 +-
 Documentation/git-range-diff.adoc           |   8 +-
 Documentation/pretty-options.adoc           |   9 +
 Makefile                                    |   2 +
 builtin/log.c                               |  17 +-
 builtin/name-rev.c                          |   9 +-
 builtin/range-diff.c                        |   2 +
 contrib/completion/git-completion.bash      |   4 +-
 log-tree.c                                  |  10 +-
 meson.build                                 |   1 +
 notes-external.c                            | 330 ++++++++++++++
 notes-external.h                            |  19 +
 notes.c                                     | 244 ++++++++---
 notes.h                                     |  32 +-
 revision.c                                  |  32 +-
 run-command.c                               |  92 +++-
 run-command.h                               |  13 +
 strbuf.c                                    |  26 +-
 strbuf.h                                    |   4 +
 t/helper/meson.build                        |   1 +
 t/helper/test-external-notes                |  64 +++
 t/helper/test-notes-external-config-reset.c |  20 +
 t/helper/test-tool.c                        |   1 +
 t/helper/test-tool.h                        |   1 +
 t/lib-notes.sh                              |  19 +
 t/t3206-range-diff.sh                       |  68 +++
 t/t3301-notes.sh                            | 461 ++++++++++++++++++++
 t/t6120-describe.sh                         |  17 +
 wrapper.c                                   | 188 +++++++-
 wrapper.h                                   |  24 +
 31 files changed, 1702 insertions(+), 84 deletions(-)
 create mode 100644 notes-external.c
 create mode 100644 notes-external.h
 create mode 100755 t/helper/test-external-notes
 create mode 100644 t/helper/test-notes-external-config-reset.c
 create mode 100644 t/lib-notes.sh

-- 
2.53.0

[PATCH 1/9] Documentation/git-range-diff: add missing notes options in synopsis

[Siddh Raman Pant]

Signed-off-by: Siddh Raman Pant <siddh.raman.pant@oracle.com>
---
 Documentation/git-range-diff.adoc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Documentation/git-range-diff.adoc b/Documentation/git-range-diff.adoc
index 880557084533..5cc5e2ed5673 100644
--- a/Documentation/git-range-diff.adoc
+++ b/Documentation/git-range-diff.adoc
@@ -11,7 +11,7 @@ SYNOPSIS
 git range-diff [--color=[<when>]] [--no-color] [<diff-options>]
 	[--no-dual-color] [--creation-factor=<factor>]
 	[--left-only | --right-only] [--diff-merges=<format>]
-	[--remerge-diff]
+	[--remerge-diff] [--no-notes | --notes[=<ref>]]
 	( <range1> <range2> | <rev1>...<rev2> | <base> <rev1> <rev2> )
 	[[--] <path>...]
 
-- 
2.53.0

Re: [PATCH 1/9] Documentation/git-range-diff: add missing notes options in synopsis

[Junio C Hamano]

Siddh Raman Pant <siddh.raman.pant@oracle.com> writes:

> Signed-off-by: Siddh Raman Pant <siddh.raman.pant@oracle.com>
> ---
>  Documentation/git-range-diff.adoc | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

This has nothing to do with "external notes" topic, no?

>
> diff --git a/Documentation/git-range-diff.adoc b/Documentation/git-range-diff.adoc
> index 880557084533..5cc5e2ed5673 100644
> --- a/Documentation/git-range-diff.adoc
> +++ b/Documentation/git-range-diff.adoc
> @@ -11,7 +11,7 @@ SYNOPSIS
>  git range-diff [--color=[<when>]] [--no-color] [<diff-options>]
>  	[--no-dual-color] [--creation-factor=<factor>]
>  	[--left-only | --right-only] [--diff-merges=<format>]
> -	[--remerge-diff]
> +	[--remerge-diff] [--no-notes | --notes[=<ref>]]
>  	( <range1> <range2> | <rev1>...<rev2> | <base> <rev1> <rev2> )
>  	[[--] <path>...]

[PATCH 2/9] notes: convert raw arg in format_display_notes() to bool

[Siddh Raman Pant]

It's used as a boolean flag, let's not use an int.

Signed-off-by: Siddh Raman Pant <siddh.raman.pant@oracle.com>
---
 log-tree.c | 3 +--
 notes.c    | 6 +++---
 notes.h    | 2 +-
 revision.c | 2 +-
 4 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/log-tree.c b/log-tree.c
index 7e048701d0c5..4503a42dde6b 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -854,10 +854,9 @@ void show_log(struct rev_info *opt)
 	}
 
 	if (opt->show_notes) {
-		int raw;
 		struct strbuf notebuf = STRBUF_INIT;
+		bool raw = (opt->commit_format == CMIT_FMT_USERFORMAT);
 
-		raw = (opt->commit_format == CMIT_FMT_USERFORMAT);
 		format_display_notes(&commit->object.oid, &notebuf,
 				     get_log_output_encoding(), raw);
 		ctx.notes_message = strbuf_detach(&notebuf, NULL);
diff --git a/notes.c b/notes.c
index 8f315e2a00d2..201f1df3dc29 100644
--- a/notes.c
+++ b/notes.c
@@ -1273,11 +1273,11 @@ void free_notes(struct notes_tree *t)
  * If the given notes_tree is NULL, the internal/default notes_tree will be
  * used instead.
  *
- * (raw != 0) gives the %N userformat; otherwise, the note message is given
+ * (raw == true) gives the %N userformat; otherwise, the note message is given
  * for human consumption.
  */
 static void format_note(struct notes_tree *t, const struct object_id *object_oid,
-			struct strbuf *sb, const char *output_encoding, int raw)
+			struct strbuf *sb, const char *output_encoding, bool raw)
 {
 	static const char utf8[] = "utf-8";
 	const struct object_id *oid;
@@ -1338,7 +1338,7 @@ static void format_note(struct notes_tree *t, const struct object_id *object_oid
 }
 
 void format_display_notes(const struct object_id *object_oid,
-			  struct strbuf *sb, const char *output_encoding, int raw)
+			  struct strbuf *sb, const char *output_encoding, bool raw)
 {
 	int i;
 	assert(display_notes_trees);
diff --git a/notes.h b/notes.h
index 6dc6d7b26548..f6410b31e1c9 100644
--- a/notes.h
+++ b/notes.h
@@ -313,7 +313,7 @@ void load_display_notes(struct display_notes_opt *opt);
  * You *must* call load_display_notes() before using this function.
  */
 void format_display_notes(const struct object_id *object_oid,
-			  struct strbuf *sb, const char *output_encoding, int raw);
+			  struct strbuf *sb, const char *output_encoding, bool raw);
 
 /*
  * Load the notes tree from each ref listed in 'refs'.  The output is
diff --git a/revision.c b/revision.c
index 599b3a66c369..cd9fcefa0a88 100644
--- a/revision.c
+++ b/revision.c
@@ -4107,7 +4107,7 @@ static int commit_match(struct commit *commit, struct rev_info *opt)
 	if (opt->show_notes) {
 		if (!buf.len)
 			strbuf_addstr(&buf, message);
-		format_display_notes(&commit->object.oid, &buf, encoding, 1);
+		format_display_notes(&commit->object.oid, &buf, encoding, true);
 	}
 
 	/*
-- 
2.53.0

[PATCH 3/9] wrapper: add sleep_nanosec

[Siddh Raman Pant]

Signed-off-by: Siddh Raman Pant <siddh.raman.pant@oracle.com>
---
 wrapper.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 wrapper.h |  1 +
 2 files changed, 50 insertions(+)

diff --git a/wrapper.c b/wrapper.c
index 16f5a63fbb61..1349255f1eb4 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -10,6 +10,7 @@
 #include "gettext.h"
 #include "strbuf.h"
 #include "trace2.h"
+#include <time.h>
 
 #ifdef HAVE_RTLGENRANDOM
 /* This is required to get access to RtlGenRandom. */
@@ -708,6 +709,54 @@ void sleep_millisec(int millisec)
 	poll(NULL, 0, millisec);
 }
 
+#ifdef GIT_WINDOWS_NATIVE
+/* No nanosleep() on Windows, so fall-back to using sleep_millisec(). */
+int sleep_nanosec(uint64_t nanosec)
+{
+	uint64_t ns_in_1ms = 1000000ULL;	/* 1 ms = 10^6 ns */
+
+	uint64_t millisec = nanosec / ns_in_1ms;
+	if (nanosec % ns_in_1ms)
+		millisec++;
+
+	/* Chunked sleep if we can't represent in integer. */
+	while (millisec > INT_MAX) {
+		sleep_millisec(INT_MAX);
+		millisec -= INT_MAX;
+	}
+
+	sleep_millisec((int)millisec);
+
+	return 0;
+}
+#else
+/* Not Windows, so use the more exact nanosleep(). */
+int sleep_nanosec(uint64_t nanosec)
+{
+	int ret;
+	struct timespec duration, remaining;
+
+	/* Construct the duration by dividing the given total (1s = 10^9ns). */
+	duration.tv_sec = nanosec / 1000000000ULL;
+	duration.tv_nsec = nanosec % 1000000000ULL;
+
+	while(1) {
+		ret = nanosleep(&duration, &remaining);
+
+		/* Continue sleeping if interrupted. */
+		if (ret == -1 && errno == EINTR) {
+			duration = remaining;
+			continue;
+		}
+
+		/* Either success or an error. */
+		break;
+	}
+
+	return ret;
+}
+#endif  /* GIT_WINDOWS_NATIVE */
+
 int xgethostname(char *buf, size_t len)
 {
 	/*
diff --git a/wrapper.h b/wrapper.h
index 15ac3bab6e97..c39992893a81 100644
--- a/wrapper.h
+++ b/wrapper.h
@@ -130,6 +130,7 @@ int warn_on_fopen_errors(const char *path);
 int open_nofollow(const char *path, int flags);
 
 void sleep_millisec(int millisec);
+int sleep_nanosec(uint64_t nanosec);
 
 enum {
 	/*
-- 
2.53.0

Re: [PATCH 3/9] wrapper: add sleep_nanosec

[Junio C Hamano]

Siddh Raman Pant <siddh.raman.pant@oracle.com> writes:

> Signed-off-by: Siddh Raman Pant <siddh.raman.pant@oracle.com>
> ---

The space above the signed-off-by line should be utilized to explain
why we want this change.  For the purpose of this series, why do we
want to sleep at nanosecond precision?

>  wrapper.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
>  wrapper.h |  1 +
>  2 files changed, 50 insertions(+)
>
> diff --git a/wrapper.c b/wrapper.c
> index 16f5a63fbb61..1349255f1eb4 100644
> --- a/wrapper.c
> +++ b/wrapper.c
> @@ -10,6 +10,7 @@
>  #include "gettext.h"
>  #include "strbuf.h"
>  #include "trace2.h"
> +#include <time.h>
>  
>  #ifdef HAVE_RTLGENRANDOM
>  /* This is required to get access to RtlGenRandom. */
> @@ -708,6 +709,54 @@ void sleep_millisec(int millisec)
>  	poll(NULL, 0, millisec);
>  }
>  
> +#ifdef GIT_WINDOWS_NATIVE
> +/* No nanosleep() on Windows, so fall-back to using sleep_millisec(). */
> +int sleep_nanosec(uint64_t nanosec)
> +{
> +	uint64_t ns_in_1ms = 1000000ULL;	/* 1 ms = 10^6 ns */
> +
> +	uint64_t millisec = nanosec / ns_in_1ms;
> +	if (nanosec % ns_in_1ms)
> +		millisec++;
> +
> +	/* Chunked sleep if we can't represent in integer. */
> +	while (millisec > INT_MAX) {
> +		sleep_millisec(INT_MAX);
> +		millisec -= INT_MAX;
> +	}
> +
> +	sleep_millisec((int)millisec);
> +
> +	return 0;
> +}
> +#else
> +/* Not Windows, so use the more exact nanosleep(). */
> +int sleep_nanosec(uint64_t nanosec)
> +{
> +	int ret;
> +	struct timespec duration, remaining;
> +
> +	/* Construct the duration by dividing the given total (1s = 10^9ns). */
> +	duration.tv_sec = nanosec / 1000000000ULL;
> +	duration.tv_nsec = nanosec % 1000000000ULL;
> +
> +	while(1) {
> +		ret = nanosleep(&duration, &remaining);
> +
> +		/* Continue sleeping if interrupted. */
> +		if (ret == -1 && errno == EINTR) {
> +			duration = remaining;
> +			continue;
> +		}
> +
> +		/* Either success or an error. */
> +		break;
> +	}
> +
> +	return ret;
> +}
> +#endif  /* GIT_WINDOWS_NATIVE */
> +
>  int xgethostname(char *buf, size_t len)
>  {
>  	/*
> diff --git a/wrapper.h b/wrapper.h
> index 15ac3bab6e97..c39992893a81 100644
> --- a/wrapper.h
> +++ b/wrapper.h
> @@ -130,6 +130,7 @@ int warn_on_fopen_errors(const char *path);
>  int open_nofollow(const char *path, int flags);
>  
>  void sleep_millisec(int millisec);
> +int sleep_nanosec(uint64_t nanosec);
>  
>  enum {
>  	/*

[PATCH 4/9] run-command: add support for timeout in command finisher

[Siddh Raman Pant]

A called command may not respond to the initial signal and will get
stuck in finish_command() -> wait_or_whine().

So let's add timeout support into the finisher so that if a deadline
occurs, we can send a force-kill signal.

The force-kill signal is in the argument because a program may trap a
signal, so it is the responsibility of caller to pass the correct kill
signal.

Assisted-by: Codex:gpt-5.5-xhigh-fast
Signed-off-by: Siddh Raman Pant <siddh.raman.pant@oracle.com>
---
 run-command.c | 92 +++++++++++++++++++++++++++++++++++++++++++++++----
 run-command.h | 13 ++++++++
 2 files changed, 98 insertions(+), 7 deletions(-)

diff --git a/run-command.c b/run-command.c
index c146a56532a1..60b84610d1f0 100644
--- a/run-command.c
+++ b/run-command.c
@@ -554,16 +554,63 @@ static inline void set_cloexec(int fd)
 		fcntl(fd, F_SETFD, flags | FD_CLOEXEC);
 }
 
-static int wait_or_whine(pid_t pid, const char *argv0, int in_signal)
+#define NS_IN_10MS 10000000ULL	/* 10 ms = 10^-2 s = 10^(9-2) ns = 10^7 ns */
+
+/* If timeout_ns == 0, no timeout happens (the timeout path is not taken). */
+static int wait_or_whine_timeout(pid_t pid, const char *argv0, int in_signal,
+				 uint64_t timeout_ns)
 {
 	int status, code = -1;
 	pid_t waiting;
 	int failed_errno = 0;
+	int flags = timeout_ns ? WNOHANG : 0;
+	bool timed_out = false;
+	uint64_t deadline_ns = getnanotime() + timeout_ns;
+
+	while(1) {
+		uint64_t current_time_ns, remaining_ns;
+		waiting = waitpid(pid, &status, flags);
+
+		/* Retry if interrupted. */
+		if (waiting < 0 && errno == EINTR)
+			continue;
+
+		/* Break if exited. */
+		if (waiting)
+			break;
+
+		/* If no timeout is specified, retry till it exits. */
+		if (!timeout_ns)
+			continue;
 
-	while ((waiting = waitpid(pid, &status, 0)) < 0 && errno == EINTR)
-		;	/* nothing */
+		current_time_ns = getnanotime();
+
+		/* If we are past the deadline, set errno and break. */
+		if (deadline_ns <= current_time_ns) {
+			errno = ETIMEDOUT;
+			timed_out = true;
+			break;
+		}
+
+		/**
+		 * Retry after a sleep(min(remaining, default_chunk)).
+		 *
+		 * We don't blindly sleep for the entire remaining time because
+		 * the process can exit early.
+		 *
+		 * The subtraction of uint64_t is safe here since we have
+		 * already established that deadline_ns > current_time_ns.
+		 */
+		remaining_ns = deadline_ns - current_time_ns;
+		sleep_nanosec(remaining_ns < NS_IN_10MS ?
+			      remaining_ns : NS_IN_10MS);
+	}
 
-	if (waiting < 0) {
+	if (timed_out) {
+		failed_errno = errno;
+		if (!in_signal)
+			error_errno("waitpid for %s timed out", argv0);
+	} else if (waiting < 0) {
 		failed_errno = errno;
 		if (!in_signal)
 			error_errno("waitpid for %s failed", argv0);
@@ -587,13 +634,28 @@ static int wait_or_whine(pid_t pid, const char *argv0, int in_signal)
 			error("waitpid is confused (%s)", argv0);
 	}
 
-	if (!in_signal)
+	/**
+	 * Signal handlers use the cleanup list while reaping children, so only
+	 * non-signal waiters (in_signal != 0) should update it.
+	 *
+	 * In case of a timeout, we keep the child registered since it is
+	 * actually not reaped so removing would be wrong. It is the
+	 * responsibility of the caller to detect the timeout and do cleanup,
+	 * like sending a kill signal using this function without a timeout.
+	 */
+	if (!in_signal && !timed_out)
 		clear_child_for_cleanup(pid);
 
 	errno = failed_errno;
 	return code;
 }
 
+/* Non-timeout wrapper for compatibility. */
+static int wait_or_whine(pid_t pid, const char *argv0, int in_signal)
+{
+	return wait_or_whine_timeout(pid, argv0, in_signal, 0);
+}
+
 static void trace_add_env(struct strbuf *dst, const char *const *deltaenv)
 {
 	struct string_list envs = STRING_LIST_INIT_DUP;
@@ -989,15 +1051,31 @@ int start_command(struct child_process *cmd)
 	return 0;
 }
 
-int finish_command(struct child_process *cmd)
+/* See comment in the header file for executive summary. */
+int finish_command_with_timeout(struct child_process *cmd, uint64_t timeout_ns,
+				int signal_on_timeout)
 {
-	int ret = wait_or_whine(cmd->pid, cmd->args.v[0], 0);
+	int ret = wait_or_whine_timeout(cmd->pid, cmd->args.v[0], 0,
+					timeout_ns);
+
+	if (timeout_ns && ret < 0 && errno == ETIMEDOUT) {
+		kill(cmd->pid, signal_on_timeout);
+		ret = wait_or_whine(cmd->pid, cmd->args.v[0], 0);
+	}
+
 	trace2_child_exit(cmd, ret);
 	child_process_clear(cmd);
 	invalidate_lstat_cache();
 	return ret;
 }
 
+/* Non-timeout wrapper for compatibility. */
+int finish_command(struct child_process *cmd)
+{
+	return finish_command_with_timeout(cmd, 0, 0);
+}
+
+
 int finish_command_in_signal(struct child_process *cmd)
 {
 	int ret = wait_or_whine(cmd->pid, cmd->args.v[0], 1);
diff --git a/run-command.h b/run-command.h
index 8ca496d7bdeb..cb1c8ba4ec01 100644
--- a/run-command.h
+++ b/run-command.h
@@ -215,6 +215,19 @@ int start_command(struct child_process *);
  */
 int finish_command(struct child_process *);
 
+/**
+ * Wait for the completion of a sub-process that was started with
+ * start_command(), but uptil a given timeout duration timeout_ns.
+ *
+ * If it has not exited after timeout_ns, signal_on_timeout is sent to the
+ * process. We don't enforce a timeout for the second wait after sending
+ * the signal (as the process cleanup needs to happen), so it will block there.
+ *
+ * If timeout_ns == 0, no timeout happens and signal_on_timeout is ignored.
+ */
+int finish_command_with_timeout(struct child_process *cmd, uint64_t timeout_ns,
+				int signal_on_timeout);
+
 int finish_command_in_signal(struct child_process *);
 
 /**
-- 
2.53.0

[PATCH 5/9] wrapper: add support for timeout and deadline in read helpers

[Siddh Raman Pant]

Add read helpers which allow a caller to enforce a timeout per read,
and a deadline for the read in case multiple reads have to be done
under a common timeout.

Assisted-by: Codex:gpt-5.5-xhigh-fast
Signed-off-by: Siddh Raman Pant <siddh.raman.pant@oracle.com>
---
 strbuf.c  |  26 +++++++++-
 strbuf.h  |   4 ++
 wrapper.c | 139 ++++++++++++++++++++++++++++++++++++++++++++++++++----
 wrapper.h |  23 +++++++++
 4 files changed, 182 insertions(+), 10 deletions(-)

diff --git a/strbuf.c b/strbuf.c
index 3e04addc22fe..b3fc7c624aa2 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -749,13 +749,15 @@ int strbuf_getline_nul(struct strbuf *sb, FILE *fp)
 	return strbuf_getdelim(sb, fp, '\0');
 }
 
-int strbuf_getwholeline_fd(struct strbuf *sb, int fd, int term)
+static int strbuf_getwholeline_fd_with(struct strbuf *sb, int fd, int term,
+				       xread_cb_t xread_cb,
+				       void *cb_data)
 {
 	strbuf_reset(sb);
 
 	while (1) {
 		char ch;
-		ssize_t len = xread(fd, &ch, 1);
+		ssize_t len = xread_cb(fd, &ch, 1, cb_data);
 		if (len <= 0)
 			return EOF;
 		strbuf_addch(sb, ch);
@@ -765,6 +767,26 @@ int strbuf_getwholeline_fd(struct strbuf *sb, int fd, int term)
 	return 0;
 }
 
+int strbuf_getwholeline_fd_deadline(struct strbuf *sb, int fd, int term,
+				    uint64_t deadline_ns)
+{
+	return strbuf_getwholeline_fd_with(sb, fd, term, xread_deadline_fn,
+					   &deadline_ns);
+}
+
+int strbuf_getwholeline_fd_timeout(struct strbuf *sb, int fd, int term,
+				   int timeout_ms)
+{
+	return strbuf_getwholeline_fd_with(sb, fd, term, xread_timeout_fn,
+					   &timeout_ms);
+}
+
+/* Non-timeout version for compatibility. */
+int strbuf_getwholeline_fd(struct strbuf *sb, int fd, int term)
+{
+	return strbuf_getwholeline_fd_timeout(sb, fd, term, 0);
+}
+
 ssize_t strbuf_read_file(struct strbuf *sb, const char *path, size_t hint)
 {
 	int fd;
diff --git a/strbuf.h b/strbuf.h
index 06e284f9cca4..f896da1277a6 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -535,6 +535,10 @@ int strbuf_appendwholeline(struct strbuf *sb, FILE *file, int term);
  * descriptor.
  */
 int strbuf_getwholeline_fd(struct strbuf *sb, int fd, int term);
+int strbuf_getwholeline_fd_timeout(struct strbuf *sb, int fd, int term,
+				   int timeout_ms);
+int strbuf_getwholeline_fd_deadline(struct strbuf *sb, int fd, int term,
+				    uint64_t deadline_ns);
 
 /**
  * Set the buffer to the path of the current working directory.
diff --git a/wrapper.c b/wrapper.c
index 1349255f1eb4..3e0d65724e47 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -9,6 +9,7 @@
 #include "parse.h"
 #include "gettext.h"
 #include "strbuf.h"
+#include "trace.h"
 #include "trace2.h"
 #include <time.h>
 
@@ -221,28 +222,129 @@ static int handle_nonblock(int fd, short poll_events, int err)
 	return 1;
 }
 
-/*
- * xread() is the same a read(), but it automatically restarts read()
- * operations with a recoverable error (EAGAIN and EINTR). xread()
+static int wait_for_fd(int fd, short poll_events, int timeout_ms)
+{
+	struct pollfd pfd;
+
+	if (timeout_ms < 0) {
+		/* Negative timeout makes no sense. */
+		errno = EINVAL;
+		return -1;
+	}
+
+	pfd.fd = fd;
+	pfd.events = poll_events;
+
+	while(1) {
+		int ret = poll(&pfd, 1, timeout_ms);
+
+		if (ret <= 0) {
+			/* Retry if interrupted. */
+			if (ret < 0 && errno == EINTR)
+				continue;
+
+			/* Set errno if timeout happened. */
+			if (ret == 0)
+				errno = ETIMEDOUT;
+
+			return -1;
+		}
+
+		/* Invalid FD passed. */
+		if (pfd.revents & POLLNVAL) {
+			errno = EBADF;
+			return -1;
+		}
+
+		/* Some error happened. */
+		if (pfd.revents & POLLERR) {
+			errno = EIO;
+			return -1;
+		}
+
+		/* HangUp => We are ready to consume output till EOF. */
+		if (pfd.revents & (poll_events | POLLHUP))
+			return 0;
+	}
+}
+
+/**
+ * xread_timeout() is the same as read(), but it automatically restarts read()
+ * operations with a recoverable error (EAGAIN and EINTR). xread_timeout()
  * DOES NOT GUARANTEE that "len" bytes is read even if the data is available.
+ *
+ * Fails with ETIMEDOUT when no bytes become available within timeout_ms
+ * milliseconds. A zero timeout disables timeout handling, so reads can
+ * block until the file descriptor is readable. Negative timeouts are invalid.
  */
-ssize_t xread(int fd, void *buf, size_t len)
+ssize_t xread_timeout(int fd, void *buf, size_t len, int timeout_ms)
 {
 	ssize_t nr;
+
 	if (len > MAX_IO_SIZE)
 		len = MAX_IO_SIZE;
+
 	while (1) {
+		if (timeout_ms && wait_for_fd(fd, POLLIN, timeout_ms))
+			return -1;
+
 		nr = read(fd, buf, len);
+
 		if (nr < 0) {
 			if (errno == EINTR)
 				continue;
-			if (handle_nonblock(fd, POLLIN, errno))
-				continue;
+
+			if (timeout_ms) {
+				if (errno == EAGAIN || errno == EWOULDBLOCK)
+					continue;
+			} else {
+				if (handle_nonblock(fd, POLLIN, errno))
+					continue;
+			}
 		}
+
 		return nr;
 	}
 }
 
+/* Non-timeout version for compatibility. */
+ssize_t xread(int fd, void *buf, size_t len)
+{
+	return xread_timeout(fd, buf, len, 0);
+}
+
+static int remaining_timeout_ms(uint64_t deadline_ns)
+{
+	uint64_t now, remaining_ns;
+
+	if (!deadline_ns)
+		return 0;
+
+	now = getnanotime();
+	if (now >= deadline_ns) {
+		errno = ETIMEDOUT;
+		return -1;
+	}
+
+	remaining_ns = deadline_ns - now;
+	return (int)((remaining_ns + 999999ULL) / 1000000ULL);
+}
+
+/* (deadline_ns = 0) disables the deadline and short-circuits to xread(). */
+ssize_t xread_deadline(int fd, void *buf, size_t len, uint64_t deadline_ns)
+{
+	int timeout_ms;
+
+	if (deadline_ns == 0)
+		return xread(fd, buf, len);
+
+	timeout_ms = remaining_timeout_ms(deadline_ns);
+	if (timeout_ms < 0)
+		return -1;
+
+	return xread_timeout(fd, buf, len, timeout_ms);
+}
+
 /*
  * xwrite() is the same a write(), but it automatically restarts write()
  * operations with a recoverable error (EAGAIN and EINTR). xwrite() DOES NOT
@@ -284,13 +386,15 @@ ssize_t xpread(int fd, void *buf, size_t len, off_t offset)
 	}
 }
 
-ssize_t read_in_full(int fd, void *buf, size_t count)
+static ssize_t read_in_full_with(int fd, void *buf, size_t count,
+				 xread_cb_t xread_cb,
+				 void *cb_data)
 {
 	char *p = buf;
 	ssize_t total = 0;
 
 	while (count > 0) {
-		ssize_t loaded = xread(fd, p, count);
+		ssize_t loaded = xread_cb(fd, p, count, cb_data);
 		if (loaded < 0)
 			return -1;
 		if (loaded == 0)
@@ -303,6 +407,25 @@ ssize_t read_in_full(int fd, void *buf, size_t count)
 	return total;
 }
 
+ssize_t read_in_full_deadline(int fd, void *buf, size_t count,
+			      uint64_t deadline_ns)
+{
+	return read_in_full_with(fd, buf, count, xread_deadline_fn,
+				 &deadline_ns);
+}
+
+ssize_t read_in_full_timeout(int fd, void *buf, size_t count, int timeout_ms)
+{
+	return read_in_full_with(fd, buf, count, xread_timeout_fn,
+				 &timeout_ms);
+}
+
+/* Non-timeout version for compatibility. */
+ssize_t read_in_full(int fd, void *buf, size_t count)
+{
+	return read_in_full_timeout(fd, buf, count, 0);
+}
+
 ssize_t write_in_full(int fd, const void *buf, size_t count)
 {
 	const char *p = buf;
diff --git a/wrapper.h b/wrapper.h
index c39992893a81..f8592599216a 100644
--- a/wrapper.h
+++ b/wrapper.h
@@ -15,6 +15,8 @@ const char *mmap_os_err(void);
 void *xmmap_gently(void *start, size_t length, int prot, int flags, int fd, off_t offset);
 int xopen(const char *path, int flags, ...);
 ssize_t xread(int fd, void *buf, size_t len);
+ssize_t xread_timeout(int fd, void *buf, size_t len, int timeout_ms);
+ssize_t xread_deadline(int fd, void *buf, size_t len, uint64_t deadline_ns);
 ssize_t xwrite(int fd, const void *buf, size_t len);
 ssize_t xpread(int fd, void *buf, size_t len, off_t offset);
 int xdup(int fd);
@@ -44,9 +46,30 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode);
 int git_mkstemp_mode(char *pattern, int mode);
 
 ssize_t read_in_full(int fd, void *buf, size_t count);
+ssize_t read_in_full_timeout(int fd, void *buf, size_t count, int timeout_ms);
+ssize_t read_in_full_deadline(int fd, void *buf, size_t count,
+			      uint64_t deadline_ns);
 ssize_t write_in_full(int fd, const void *buf, size_t count);
 ssize_t pread_in_full(int fd, void *buf, size_t count, off_t offset);
 
+typedef ssize_t xread_cb_t(int fd, void *buf, size_t len, const void *cb_data);
+
+static inline ssize_t xread_timeout_fn(int fd, void *buf, size_t len,
+				       const void *cb_data)
+{
+	const int *timeout_ms = cb_data;
+
+	return xread_timeout(fd, buf, len, *timeout_ms);
+}
+
+static inline ssize_t xread_deadline_fn(int fd, void *buf, size_t len,
+					const void *cb_data)
+{
+	const uint64_t *deadline_ns = cb_data;
+
+	return xread_deadline(fd, buf, len, *deadline_ns);
+}
+
 static inline ssize_t write_str_in_full(int fd, const char *str)
 {
 	return write_in_full(fd, str, strlen(str));
-- 
2.53.0

[PATCH 6/9] t3301: cover generic displayed notes behavior

[Siddh Raman Pant]

Displayed notes already participate in common log behavior.
Add explicit coverage for raw notes formatting, --no-notes
suppression, explicit notes refs, and --grep matching before
teaching external notes to feed the same display path.

Assisted-by: Codex:gpt-5.5-xhigh-fast
Signed-off-by: Siddh Raman Pant <siddh.raman.pant@oracle.com>
---
 t/t3301-notes.sh | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/t/t3301-notes.sh b/t/t3301-notes.sh
index d6c50460d086..27439010dfbc 100755
--- a/t/t3301-notes.sh
+++ b/t/t3301-notes.sh
@@ -885,6 +885,30 @@ test_expect_success '--show-notes=ref accumulates' '
 	test_cmp expect-both-reversed actual
 '
 
+test_expect_success 'displayed notes honor raw notes formatting' '
+	git show -s --format=%N >actual &&
+	test_grep "^order test$" actual &&
+	! grep "Notes" actual
+'
+
+test_expect_success 'displayed notes are suppressed by --no-notes' '
+	git log --no-notes -1 >actual &&
+	test_cmp expect-not-other actual
+'
+
+test_expect_success 'explicit notes ref replaces default displayed notes' '
+	git log --notes=other -1 >actual &&
+	test_cmp expect-other actual
+'
+
+test_expect_success 'displayed notes are used for grep matching' '
+	commit=$(git rev-parse HEAD) &&
+	git log --grep="order test" -1 >actual &&
+	test_grep "^commit $commit$" actual &&
+	git log --no-notes --grep="order test" -1 >actual &&
+	test_must_be_empty actual
+'
+
 test_expect_success 'Allow notes on non-commits (trees, blobs, tags)' '
 	test_config core.notesRef refs/notes/other &&
 	echo "Note on a tree" >expect &&
-- 
2.53.0

[PATCH 7/9] notes: support an external command to display notes

[Siddh Raman Pant]

git notes is a very very helpful feature to show user-supplied
information about a commit alongside its message transparently.

For distributed teams working on large git repos (huge number of
branches/refs, files, etc.) and using the notes feature to mark
information on git commits, a TOCTOU race can happen due to very
large size of the repo and notes ref:
	- Person A updates a note for commit X.
	- Person A pushes the notes but it takes some time.
	- Person B fetches notes and doesn't find the updated note.
	- Person B can come to know of it only when he overwrites it
	  and encounters a push failure.

This problem excaberates on scale.

One solution to this is a realtime fetch or faster updation via
external means, but unfortunately we lose the coherence in the
display of information, and the user would end up reinventing
git log.

So let's add support for an external command to display the notes.

We split the addition of documentation and tests from this commit for
easier review. The new help text added in Documentation/ in the next
commit should make the usage clear.

Assisted-by: Codex:gpt-5.5-xhigh-fast
Signed-off-by: Siddh Raman Pant <siddh.raman.pant@oracle.com>
---
 Makefile             |   2 +
 builtin/log.c        |  17 ++-
 builtin/name-rev.c   |   9 +-
 builtin/range-diff.c |   2 +
 log-tree.c           |   7 +-
 meson.build          |   1 +
 notes-external.c     | 330 +++++++++++++++++++++++++++++++++++++++++++
 notes-external.h     |  19 +++
 notes.c              | 242 ++++++++++++++++++++++++-------
 notes.h              |  32 ++++-
 revision.c           |  32 ++++-
 11 files changed, 633 insertions(+), 60 deletions(-)
 create mode 100644 notes-external.c
 create mode 100644 notes-external.h

diff --git a/Makefile b/Makefile
index c739ae78d0ef..a919bdd75f01 100644
--- a/Makefile
+++ b/Makefile
@@ -838,6 +838,7 @@ TEST_BUILTINS_OBJS += test-match-trees.o
 TEST_BUILTINS_OBJS += test-mergesort.o
 TEST_BUILTINS_OBJS += test-mktemp.o
 TEST_BUILTINS_OBJS += test-name-hash.o
+TEST_BUILTINS_OBJS += test-notes-external-config-reset.o
 TEST_BUILTINS_OBJS += test-online-cpus.o
 TEST_BUILTINS_OBJS += test-pack-deltas.o
 TEST_BUILTINS_OBJS += test-pack-mtimes.o
@@ -1209,6 +1210,7 @@ LIB_OBJS += negotiator/default.o
 LIB_OBJS += negotiator/noop.o
 LIB_OBJS += negotiator/skipping.o
 LIB_OBJS += notes-cache.o
+LIB_OBJS += notes-external.o
 LIB_OBJS += notes-merge.o
 LIB_OBJS += notes-utils.o
 LIB_OBJS += notes.o
diff --git a/builtin/log.c b/builtin/log.c
index 8c0939dd42ad..bed4c1576f2d 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -1337,9 +1337,24 @@ static void get_notes_args(struct strvec *arg, struct rev_info *rev)
 		   (rev->notes_opt.use_default_notes == -1 &&
 		    !rev->notes_opt.extra_notes_refs.nr)) {
 		strvec_push(arg, "--notes");
-	} else {
+	} else if (rev->notes_opt.extra_notes_refs.nr) {
 		for_each_string_list(&rev->notes_opt.extra_notes_refs, get_notes_refs, arg);
+	} else if (rev->notes_opt.use_external_notes <= 0) {
+		/*
+		 * rev->show_notes can stay set after
+		 * --external-notes --no-external-notes.
+		 *
+		 * Since range-diff's child log starts with
+		 * --show-notes-by-default, explicitly suppress
+		 * notes when no notes source remains.
+		 */
+		strvec_push(arg, "--no-notes");
 	}
+
+	if (rev->notes_opt.use_external_notes > 0)
+		strvec_push(arg, "--external-notes");
+	else if (rev->notes_opt.use_external_notes == 0)
+		strvec_push(arg, "--no-external-notes");
 }
 
 static void generate_shortlog_cover_letter(struct shortlog *log,
diff --git a/builtin/name-rev.c b/builtin/name-rev.c
index 60cbbfb4b7d1..95d5e076e24b 100644
--- a/builtin/name-rev.c
+++ b/builtin/name-rev.c
@@ -277,6 +277,7 @@ struct name_ref_data {
 struct pretty_format {
 	struct pretty_print_context ctx;
 	struct userformat_want want;
+	bool show_external_notes;
 };
 
 enum command_type {
@@ -525,9 +526,9 @@ static const char *get_format_rev(const struct commit *c,
 	if (format_ctx->want.notes) {
 		struct strbuf notebuf = STRBUF_INIT;
 
-		format_display_notes(&c->object.oid, &notebuf,
-				     get_log_output_encoding(),
-				     format_ctx->ctx.fmt == CMIT_FMT_USERFORMAT);
+		format_display_notes(c, &notebuf, get_log_output_encoding(),
+				     format_ctx->ctx.fmt == CMIT_FMT_USERFORMAT,
+				     format_ctx->show_external_notes);
 		format_ctx->ctx.notes_message = strbuf_detach(&notebuf, NULL);
 	}
 
@@ -878,6 +879,8 @@ int cmd_format_rev(int argc,
 			enable_ref_display_notes(&format_notes_opt,
 						 &ignore_show_notes,
 						 n->string);
+		format_pp.show_external_notes =
+			display_notes_use_external(&format_notes_opt);
 		load_display_notes(&format_notes_opt);
 	}
 
diff --git a/builtin/range-diff.c b/builtin/range-diff.c
index e54c0f7fe156..41c27250404a 100644
--- a/builtin/range-diff.c
+++ b/builtin/range-diff.c
@@ -56,6 +56,8 @@ int cmd_range_diff(int argc,
 		OPT_PASSTHRU_ARGV(0, "notes", &log_arg,
 				  N_("notes"), N_("passed to 'git log'"),
 				  PARSE_OPT_OPTARG),
+		OPT_PASSTHRU_ARGV(0, "external-notes", &log_arg, NULL,
+				  N_("passed to 'git log'"), PARSE_OPT_NOARG),
 		OPT_PASSTHRU_ARGV(0, "diff-merges", &diff_merges_arg,
 				  N_("style"), N_("passed to 'git log'"), 0),
 		OPT_CALLBACK(0, "max-memory", &range_diff_opts.max_memory,
diff --git a/log-tree.c b/log-tree.c
index 4503a42dde6b..3289a085f66b 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -856,9 +856,12 @@ void show_log(struct rev_info *opt)
 	if (opt->show_notes) {
 		struct strbuf notebuf = STRBUF_INIT;
 		bool raw = (opt->commit_format == CMIT_FMT_USERFORMAT);
+		const struct display_notes_opt *notes_opt = &opt->notes_opt;
+
+		format_display_notes(commit, &notebuf,
+				     get_log_output_encoding(), raw,
+				     display_notes_use_external(notes_opt));
 
-		format_display_notes(&commit->object.oid, &notebuf,
-				     get_log_output_encoding(), raw);
 		ctx.notes_message = strbuf_detach(&notebuf, NULL);
 	}
 
diff --git a/meson.build b/meson.build
index de917bcf1146..21cdbc15aa18 100644
--- a/meson.build
+++ b/meson.build
@@ -397,6 +397,7 @@ libgit_sources = [
   'notes-merge.c',
   'notes-utils.c',
   'notes.c',
+  'notes-external.c',
   'object-file-convert.c',
   'object-file.c',
   'object-name.c',
diff --git a/notes-external.c b/notes-external.c
new file mode 100644
index 000000000000..7d6b2c6060e0
--- /dev/null
+++ b/notes-external.c
@@ -0,0 +1,330 @@
+#include "git-compat-util.h"
+#include "gettext.h"
+#include "hex.h"
+#include "notes-external.h"
+#include "run-command.h"
+#include "sigchain.h"
+#include "strbuf.h"
+#include "trace.h"
+
+#define convert_ms_to_ns(ms) (uint64_t)(ms) * 1000000ULL
+#define convert_ns_to_ms(ns) (uint64_t)(ns) / 1000000ULL
+#define EXTERNAL_NOTES_TERMINATE_GRACE_NS 100000000ULL	/* 100 ms = 10^8 ns */
+#define EXTERNAL_NOTES_READ_CHUNK_SIZE 16384	/* (16 * 1024) bytes */
+
+#ifdef GIT_WINDOWS_NATIVE
+#define EXTERNAL_NOTES_FORCE_KILL_SIGNAL SIGTERM
+#else
+#define EXTERNAL_NOTES_FORCE_KILL_SIGNAL SIGKILL
+#endif
+
+/* ------------------------------------------------------------------------- */
+
+/* Configuration helpers. */
+
+static char *external_notes_command;
+static char *external_notes_command_name_value;
+static uint64_t external_notes_read_timeout_ns = convert_ms_to_ns(100);
+static int external_notes_command_failed;
+static int external_notes_for_grep;
+static bool external_notes_started;
+
+void set_external_notes_command(const char *command)
+{
+	FREE_AND_NULL(external_notes_command);
+	if (command && *command)
+		external_notes_command = xstrdup(command);
+}
+
+void set_external_notes_command_name(const char *name)
+{
+	FREE_AND_NULL(external_notes_command_name_value);
+	if (name && *name)
+		external_notes_command_name_value = xstrdup(name);
+}
+
+void set_external_notes_command_timeout_ms(int timeout_ms)
+{
+	if (timeout_ms < 0)
+		BUG("negative notes.externalCommandTimeoutMs");
+
+	external_notes_read_timeout_ns = convert_ms_to_ns(timeout_ms);
+}
+
+void reset_external_notes_command(void)
+{
+	if (external_notes_started)
+		BUG("cannot reset external notes config while cmd is running");
+
+	FREE_AND_NULL(external_notes_command);
+	FREE_AND_NULL(external_notes_command_name_value);
+	external_notes_read_timeout_ns = convert_ms_to_ns(100);
+	external_notes_command_failed = 0;
+	external_notes_for_grep = 0;
+}
+
+int external_notes_command_configured(void)
+{
+	return external_notes_command && !external_notes_command_failed;
+}
+
+const char *external_notes_command_name(void)
+{
+	return external_notes_command_name_value ?
+		external_notes_command_name_value : "external";
+}
+
+int external_notes_command_timeout_ms(void)
+{
+	return (int)convert_ns_to_ms(external_notes_read_timeout_ns);
+}
+
+void set_external_notes_for_grep(int enabled)
+{
+	external_notes_for_grep = enabled;
+}
+
+int external_notes_for_grep_enabled(void)
+{
+	return external_notes_for_grep;
+}
+
+/* ------------------------------------------------------------------------- */
+
+/* Process management helpers. */
+
+static struct child_process external_notes_process = CHILD_PROCESS_INIT;
+static FILE *external_notes_in;
+static int external_notes_out_fd = -1;
+
+static void mute_routine(const char *msg UNUSED, va_list params UNUSED)
+{
+	/* do nothing */
+}
+
+static void close_external_notes_process_pipes(struct child_process *process)
+{
+	sigchain_push(SIGPIPE, SIG_IGN);
+
+	if (external_notes_in) {
+		fclose(external_notes_in);
+		external_notes_in = NULL;
+	} else {
+		close(process->in);
+	}
+
+	if (external_notes_out_fd >= 0) {
+		close(external_notes_out_fd);
+		external_notes_out_fd = -1;
+	} else {
+		close(process->out);
+	}
+
+	sigchain_pop(SIGPIPE);
+}
+
+/* We set this as callback later, so can't have void argument. */
+static void cleanup_external_notes_process(struct child_process *process)
+{
+	report_fn old_error = NULL;
+
+	/**
+	 * The helper may still be sleeping with its pipes open, or may not
+	 * exit promptly after EOF. Ask it to stop, then use a bounded wait
+	 * that escalates if it ignores the signal.
+	 */
+	kill(process->pid, SIGTERM);
+	old_error = get_error_routine();
+	set_error_routine(mute_routine);
+
+	close_external_notes_process_pipes(process);
+	finish_command_with_timeout(process, EXTERNAL_NOTES_TERMINATE_GRACE_NS,
+				    EXTERNAL_NOTES_FORCE_KILL_SIGNAL);
+
+	if (old_error)
+		set_error_routine(old_error);
+
+	external_notes_started = false;
+}
+
+static void stop_external_notes_process(void)
+{
+	if (!external_notes_started)
+		return;
+
+	external_notes_process.clean_on_exit = 0;
+	cleanup_external_notes_process(&external_notes_process);
+	child_process_init(&external_notes_process);
+}
+
+static int fail_external_notes_command(void)
+{
+	if (!external_notes_command_failed)
+		warning(_("notes.externalCommand failed: %s"),
+			external_notes_command);
+
+	external_notes_command_failed = 1;
+	stop_external_notes_process();
+	return -1;
+}
+
+static int start_external_notes_command(void)
+{
+	struct child_process *cmd = &external_notes_process;
+
+	if (external_notes_started)
+		return 0;
+
+	if (!external_notes_command || external_notes_command_failed)
+		return -1;
+
+	child_process_init(cmd);
+	strvec_push(&cmd->args, external_notes_command);
+	cmd->use_shell = 1;
+	cmd->in = -1;
+	cmd->out = -1;
+	cmd->clean_on_exit = 1;
+	cmd->clean_on_exit_handler = cleanup_external_notes_process;
+	cmd->trace2_child_class = "notes-external";
+
+	if (start_command(cmd))
+		return fail_external_notes_command();
+
+	external_notes_in = xfdopen(cmd->in, "wb");
+	external_notes_out_fd = cmd->out;
+	external_notes_started = true;
+	return 0;
+}
+
+/* ------------------------------------------------------------------------- */
+
+/* Command parser. Essentially the main() function of this file. */
+int format_external_note(const struct object_id *object_oid,
+			 struct strbuf *note_buf)
+{
+	struct strbuf status = STRBUF_INIT;
+	char commit_id_hex_str[GIT_MAX_HEXSZ + 1];
+	const char *arg;
+	char *end;
+	char ch;
+	unsigned long len;
+	uint64_t deadline_ns;
+	bool input_fail;
+	int ret = 0;
+
+	if (start_external_notes_command())
+		return -1;
+
+	/* Fetch the commit ID hex. */
+	oid_to_hex_r(commit_id_hex_str, object_oid);
+
+	/* Pass the input to the external command. */
+	sigchain_push(SIGPIPE, SIG_IGN);
+	input_fail = fprintf(external_notes_in, "%s\n", commit_id_hex_str) < 0
+		     || fflush(external_notes_in) != 0;
+	sigchain_pop(SIGPIPE);
+
+	if (input_fail)
+		goto out_fail;
+
+	if (external_notes_read_timeout_ns == 0)
+		deadline_ns = 0;
+	else
+		deadline_ns = getnanotime() + external_notes_read_timeout_ns;
+
+	/**
+	 * The output for each commit is either of the two:
+	 * 	"{commit id} missing\n"
+	 * 	"{commit id} ok {num_bytes}\n{str_of_num_bytes}\n"
+	 *
+	 * We can have "\r\n" instead of "\n" due to Windows.
+	 */
+
+	/* Read the first line with its delimiter. */
+	if (strbuf_getwholeline_fd_deadline(&status, external_notes_out_fd,
+					    '\n', deadline_ns) == EOF)
+		goto out_fail;
+
+	/* Reject EOF-terminated partial lines. */
+	if (!status.len || status.buf[status.len - 1] != '\n')
+		goto out_fail;
+
+	/**
+	 * Strip LF and then optional CR so both LF and CRLF protocol lines
+	 * are accepted.
+	 */
+	strbuf_setlen(&status, status.len - 1);
+	strbuf_strip_suffix(&status, "\r");
+
+	/* Check if line starts with the commit ID. */
+	if (!skip_prefix(status.buf, commit_id_hex_str, &arg))
+		goto out_fail;
+
+	if (*arg++ != ' ')  /* After commit ID there should be a space. */
+		goto out_fail;
+
+	if (strcmp(arg, "missing") == 0)  /* No note available. */
+		goto out_success;  /* Ending newline is already ensured. */
+
+	if (!skip_prefix(arg, "ok ", &arg))  /* Neither missing nor ok. */
+		goto out_fail;
+
+	/* We are in "ok" case. */
+
+	/* The next thing is length of the note. It must be unsigned digits. */
+	if (!isdigit(*arg))
+		goto out_fail;
+
+	/* Get the length of note. */
+	errno = 0;
+	len = strtoul(arg, &end, 10);
+	if (errno != 0 || *end != '\0' || end == arg)
+		goto out_fail;
+
+	/* Ending newline is already ensured. */
+
+	/* Read the trailing note in bounded-chunks. */
+	while (note_buf->len < len) {
+		ssize_t got;
+		size_t remaining = len - note_buf->len;
+		size_t want = remaining < EXTERNAL_NOTES_READ_CHUNK_SIZE ?
+			      remaining : EXTERNAL_NOTES_READ_CHUNK_SIZE;
+
+		strbuf_grow(note_buf, want);
+
+		got = read_in_full_deadline(external_notes_out_fd,
+					    note_buf->buf + note_buf->len,
+					    want, deadline_ns);
+		if (got < 0 || (size_t)got != want)
+			goto out_fail;
+
+		strbuf_setlen(note_buf, note_buf->len + (size_t)got);
+	}
+
+	/* Ensure the ending newline (LF/CRLF) after the note. */
+	if (xread_deadline(external_notes_out_fd, &ch, 1, deadline_ns) != 1)
+		goto out_fail;
+
+	if (ch != '\n') {  /* Not a LF. */
+		if (ch != '\r')  /* Not a CRLF. */
+			goto out_fail;
+
+		/* We have '\r', let's read the next char. */
+		if (xread_deadline(external_notes_out_fd, &ch, 1,
+				   deadline_ns) != 1)
+			goto out_fail;
+
+		if (ch != '\n')  /* Not a CRLF. */
+			goto out_fail;
+	}
+
+	goto out_success;
+
+out_fail:
+	ret = fail_external_notes_command();
+out_success:
+	strbuf_release(&status);
+	return ret;
+}
+
+/* ------------------------------------------------------------------------- */
diff --git a/notes-external.h b/notes-external.h
new file mode 100644
index 000000000000..e49a50b09063
--- /dev/null
+++ b/notes-external.h
@@ -0,0 +1,19 @@
+#ifndef NOTES_EXTERNAL_H
+#define NOTES_EXTERNAL_H
+
+struct object_id;
+struct strbuf;
+
+void set_external_notes_command(const char *command);
+void set_external_notes_command_name(const char *name);
+void set_external_notes_command_timeout_ms(int timeout_ms);
+void set_external_notes_for_grep(int enabled);
+void reset_external_notes_command(void);
+int external_notes_command_configured(void);
+const char *external_notes_command_name(void);
+int external_notes_command_timeout_ms(void);
+int external_notes_for_grep_enabled(void);
+int format_external_note(const struct object_id *object_oid,
+			 struct strbuf *out);
+
+#endif  /* NOTES_EXTERNAL_H */
diff --git a/notes.c b/notes.c
index 201f1df3dc29..0ff8ba94afc5 100644
--- a/notes.c
+++ b/notes.c
@@ -3,9 +3,12 @@
 
 #include "git-compat-util.h"
 #include "config.h"
+#include "commit.h"
 #include "environment.h"
+#include "gettext.h"
 #include "hex.h"
 #include "notes.h"
+#include "notes-external.h"
 #include "object-file.h"
 #include "object-name.h"
 #include "odb.h"
@@ -983,18 +986,56 @@ void string_list_add_refs_from_colon_sep(struct string_list *list,
 	free(globs_copy);
 }
 
+struct notes_display_config_data {
+	int load_refs;
+	int load_command;
+};
+
 static int notes_display_config(const char *k, const char *v,
-				const struct config_context *ctx UNUSED,
+				const struct config_context *ctx,
 				void *cb)
 {
-	int *load_refs = cb;
+	struct notes_display_config_data *data = cb;
 
-	if (*load_refs && !strcmp(k, "notes.displayref")) {
+	if (data->load_refs && !strcmp(k, "notes.displayref")) {
 		if (!v)
 			return config_error_nonbool(k);
 		string_list_add_refs_by_glob(&display_notes_refs, v);
 	}
 
+	if (data->load_command && !strcmp(k, "notes.externalcommand")) {
+		if (!v)
+			return config_error_nonbool(k);
+
+		set_external_notes_command(v);
+	}
+
+	if (data->load_command && !strcmp(k, "notes.externalcommandname")) {
+		if (!v)
+			return config_error_nonbool(k);
+
+		if (strchr(v, '\n') || strchr(v, '\r'))
+			return error(_("notes.externalCommandName must not contain a newline"));
+
+		set_external_notes_command_name(v);
+	}
+
+	if (data->load_command && !strcmp(k, "notes.externalcommandtimeoutms")) {
+		int timeout_ms;
+
+		if (!v)
+			return config_error_nonbool(k);
+
+		timeout_ms = git_config_int(k, v, ctx->kvi);
+		if (timeout_ms < 0)
+			return error(_("notes.externalCommandTimeoutMs must be non-negative"));
+
+		set_external_notes_command_timeout_ms(timeout_ms);
+	}
+
+	if (data->load_command && !strcmp(k, "notes.externalcommandforgrep"))
+		set_external_notes_for_grep(git_config_bool(k, v));
+
 	return 0;
 }
 
@@ -1075,6 +1116,7 @@ void init_display_notes(struct display_notes_opt *opt)
 {
 	memset(opt, 0, sizeof(*opt));
 	opt->use_default_notes = -1;
+	opt->use_external_notes = -1;
 	string_list_init_dup(&opt->extra_notes_refs);
 }
 
@@ -1086,6 +1128,7 @@ void release_display_notes(struct display_notes_opt *opt)
 void enable_default_display_notes(struct display_notes_opt *opt, int *show_notes)
 {
 	opt->use_default_notes = 1;
+	opt->default_notes_suppressed_by_external = 0;
 	*show_notes = 1;
 }
 
@@ -1102,31 +1145,85 @@ void enable_ref_display_notes(struct display_notes_opt *opt, int *show_notes,
 void disable_display_notes(struct display_notes_opt *opt, int *show_notes)
 {
 	opt->use_default_notes = -1;
+	opt->use_external_notes = -1;
+	opt->default_notes_suppressed_by_external = 0;
 	string_list_clear(&opt->extra_notes_refs, 0);
 	*show_notes = 0;
 }
 
+/*
+ * Resolve the default-notes tri-state in one place. Callers must not test
+ * use_default_notes directly unless they specifically need the unresolved
+ * command-line state.
+ */
+static bool display_notes_use_default(const struct display_notes_opt *opt)
+{
+	/* Options aren't specified, default to true. */
+	if (!opt)
+		return true;
+
+	/* Explicitly enabled. */
+	if (opt->use_default_notes > 0)
+		return true;
+
+	/* Undefined and no explicit notes-ref specified, default to true. */
+	if (opt->use_default_notes == -1 && !opt->extra_notes_refs.nr)
+		return true;
+
+	return false;
+}
+
+/*
+ * Resolve the external-notes tri-state. The unset value follows the resolved
+ * default-notes decision, which means "git log" runs the helper by default
+ * but "git log --notes=<ref>" does not.
+ */
+bool display_notes_use_external(const struct display_notes_opt *opt)
+{
+	/* Options aren't specified, default to true. */
+	if (!opt)
+		return true;
+
+	/* Explicitly enabled. */
+	if (opt->use_external_notes > 0)
+		return true;
+
+	/* Undefined and to use default notes set, default to true. */
+	if (opt->use_external_notes < 0 && display_notes_use_default(opt))
+		return true;
+
+	return false;
+}
+
 void load_display_notes(struct display_notes_opt *opt)
 {
 	char *display_ref_env;
-	int load_config_refs = 0;
+	struct notes_display_config_data config = { 0, 0 };
+	struct notes_display_config_data protected_config = { 0, 0 };
+	bool use_default_notes = display_notes_use_default(opt);
+	bool use_external_notes = display_notes_use_external(opt);
+
 	display_notes_refs.strdup_strings = 1;
+	reset_external_notes_command();
 
 	assert(!display_notes_trees);
 
-	if (!opt || opt->use_default_notes > 0 ||
-	    (opt->use_default_notes == -1 && !opt->extra_notes_refs.nr)) {
+	if (use_default_notes) {
 		string_list_append_nodup(&display_notes_refs, default_notes_ref(the_repository));
 		display_ref_env = getenv(GIT_NOTES_DISPLAY_REF_ENVIRONMENT);
 		if (display_ref_env) {
 			string_list_add_refs_from_colon_sep(&display_notes_refs,
 							    display_ref_env);
-			load_config_refs = 0;
+			config.load_refs = 0;
 		} else
-			load_config_refs = 1;
+			config.load_refs = 1;
 	}
 
-	repo_config(the_repository, notes_display_config, &load_config_refs);
+	if (use_external_notes)
+		protected_config.load_command = 1;
+
+	repo_config(the_repository, notes_display_config, &config);
+	git_protected_config(notes_display_config, &protected_config);
 
 	if (opt) {
 		struct string_list_item *item;
@@ -1266,47 +1363,31 @@ void free_notes(struct notes_tree *t)
 }
 
 /*
- * Fill the given strbuf with the notes associated with the given object.
+ * Append one already-loaded note message to the given strbuf.
  *
- * If the given notes_tree structure is not initialized, it will be auto-
- * initialized to the default value (see documentation for init_notes() above).
- * If the given notes_tree is NULL, the internal/default notes_tree will be
- * used instead.
+ * Notes read from refs and notes obtained from notes.externalCommand both use
+ * this helper so they share the same encoding, header, and indentation rules.
  *
  * (raw == true) gives the %N userformat; otherwise, the note message is given
  * for human consumption.
  */
-static void format_note(struct notes_tree *t, const struct object_id *object_oid,
-			struct strbuf *sb, const char *output_encoding, bool raw)
+static void format_note_data(const char *ref, const char *msg, size_t msglen,
+			     struct strbuf *sb, const char *output_encoding,
+			     bool raw, bool literal_ref)
 {
 	static const char utf8[] = "utf-8";
-	const struct object_id *oid;
-	char *msg, *msg_p;
-	unsigned long linelen, msglen;
-	enum object_type type;
-
-	if (!t)
-		t = &default_notes_tree;
-	if (!t->initialized)
-		init_notes(t, NULL, NULL, 0);
-
-	oid = get_note(t, object_oid);
-	if (!oid)
-		return;
-
-	if (!(msg = odb_read_object(the_repository->objects, oid, &type, &msglen)) ||
-	    type != OBJ_BLOB) {
-		free(msg);
-		return;
-	}
+	char *reencoded = NULL;
+	const char *msg_p, *msg_end;
 
+	/* Convert the note text from UTF-8 to the requested output encoding. */
 	if (output_encoding && *output_encoding &&
 	    !is_encoding_utf8(output_encoding)) {
-		char *reencoded = reencode_string(msg, output_encoding, utf8);
+		size_t reencoded_len;
+		reencoded = reencode_string_len(msg, msglen, output_encoding,
+						 utf8, &reencoded_len);
 		if (reencoded) {
-			free(msg);
 			msg = reencoded;
-			msglen = strlen(msg);
+			msglen = reencoded_len;
 		}
 	}
 
@@ -1314,37 +1395,100 @@ static void format_note(struct notes_tree *t, const struct object_id *object_oid
 	if (msglen && msg[msglen - 1] == '\n')
 		msglen--;
 
+	/* Raw mode is the %N userformat, so it omits the "Notes" header. */
 	if (!raw) {
-		const char *ref = t->ref;
-		if (!ref || !strcmp(ref, GIT_NOTES_DEFAULT_REF)) {
+		if (!ref)
 			strbuf_addstr(sb, "\nNotes:\n");
-		} else {
-			skip_prefix(ref, "refs/", &ref);
-			skip_prefix(ref, "notes/", &ref);
+		else if (!literal_ref && !strcmp(ref, GIT_NOTES_DEFAULT_REF))
+			strbuf_addstr(sb, "\nNotes:\n");
+		else {
+			if (!literal_ref) {
+				skip_prefix(ref, "refs/", &ref);
+				skip_prefix(ref, "notes/", &ref);
+			}
 			strbuf_addf(sb, "\nNotes (%s):\n", ref);
 		}
 	}
 
-	for (msg_p = msg; msg_p < msg + msglen; msg_p += linelen + 1) {
-		linelen = strchrnul(msg_p, '\n') - msg_p;
+	msg_end = msg + msglen;
+	for (msg_p = msg; msg_p < msg_end; ) {
+		const char *eol = memchr(msg_p, '\n', msg_end - msg_p);
+		size_t linelen = eol ? eol - msg_p : msg_end - msg_p;
 
+		/* Human output indents note body lines under the header. */
 		if (!raw)
 			strbuf_addstr(sb, "    ");
+
 		strbuf_add(sb, msg_p, linelen);
 		strbuf_addch(sb, '\n');
+
+		msg_p += linelen;
+		if (msg_p < msg_end)
+			msg_p++;
+	}
+
+	free(reencoded);
+}
+
+/*
+ * Fill the given strbuf with the notes associated with the given object.
+ *
+ * If the given notes_tree structure is not initialized, it will be auto-
+ * initialized to the default value (see documentation for init_notes() above).
+ * If the given notes_tree is NULL, the internal/default notes_tree will be
+ * used instead.
+ */
+static void format_note_from_tree(struct notes_tree *t,
+				  const struct object_id *object_oid,
+				  struct strbuf *sb,
+				  const char *output_encoding, bool raw)
+{
+	const struct object_id *oid;
+	char *msg;
+	unsigned long msglen;
+	enum object_type type;
+
+	if (!t)
+		t = &default_notes_tree;
+	if (!t->initialized)
+		init_notes(t, NULL, NULL, 0);
+
+	oid = get_note(t, object_oid);
+	if (!oid)
+		return;
+
+	if (!(msg = odb_read_object(the_repository->objects, oid, &type, &msglen)) ||
+	    type != OBJ_BLOB) {
+		free(msg);
+		return;
 	}
 
+	format_note_data(t->ref, msg, msglen, sb, output_encoding, raw, false);
+
 	free(msg);
 }
 
-void format_display_notes(const struct object_id *object_oid,
-			  struct strbuf *sb, const char *output_encoding, bool raw)
+void format_display_notes(const struct commit *commit,
+			  struct strbuf *sb, const char *output_encoding,
+			  bool raw, bool show_external)
 {
 	int i;
+	const struct object_id *commit_oid = &commit->object.oid;
+
 	assert(display_notes_trees);
 	for (i = 0; display_notes_trees[i]; i++)
-		format_note(display_notes_trees[i], object_oid, sb,
-			    output_encoding, raw);
+		format_note_from_tree(display_notes_trees[i], commit_oid, sb,
+				      output_encoding, raw);
+
+	if (show_external && external_notes_command_configured()) {
+		struct strbuf out = STRBUF_INIT;
+
+		if (format_external_note(commit_oid, &out) == 0 && out.len)
+			format_note_data(external_notes_command_name(),
+					 out.buf, out.len, sb,
+					 output_encoding, raw, true);
+		strbuf_release(&out);
+	}
 }
 
 int copy_note(struct notes_tree *t,
diff --git a/notes.h b/notes.h
index f6410b31e1c9..748af70e34af 100644
--- a/notes.h
+++ b/notes.h
@@ -6,6 +6,7 @@
 struct object_id;
 struct repository;
 struct strbuf;
+struct commit;
 
 /*
  * Function type for combining two notes annotating the same object.
@@ -264,6 +265,20 @@ struct display_notes_opt {
 	 */
 	int use_default_notes;
 
+	/*
+	 * Less than `0` is "unset", which means external notes are shown iff
+	 * the default notes are shown. Otherwise, treat it like a boolean.
+	 */
+	int use_external_notes;
+
+	/*
+	 * Tracks the synthetic "default notes off" state introduced by
+	 * `--external-notes`, so a later deprecated `--show-notes=<ref>`
+	 * can still preserve its historical additive behavior without
+	 * overriding an explicit `--no-standard-notes`.
+	 */
+	int default_notes_suppressed_by_external;
+
 	/*
 	 * A list of globs (in the same style as notes.displayRef) where
 	 * notes should be loaded from.
@@ -304,16 +319,27 @@ void disable_display_notes(struct display_notes_opt *opt, int *show_notes);
 void load_display_notes(struct display_notes_opt *opt);
 
 /*
- * Append notes for the given 'object_sha1' from all trees set up by
+ * Return true if notes.externalCommand should be used for 'opt'.
+ *
+ * 'opt' may be NULL.
+ */
+bool display_notes_use_external(const struct display_notes_opt *opt);
+
+/*
+ * Append notes for the given commit from all trees set up by
  * load_display_notes() to 'sb'.
  *
  * If 'raw' is false the note will be indented by 4 places and
  * a 'Notes (refname):' header added.
  *
+ * If 'show_external' is true then notes.externalCommand will be used to append
+ * the note from external source.
+ *
  * You *must* call load_display_notes() before using this function.
  */
-void format_display_notes(const struct object_id *object_oid,
-			  struct strbuf *sb, const char *output_encoding, bool raw);
+void format_display_notes(const struct commit *commit,
+			  struct strbuf *sb, const char *output_encoding,
+			  bool raw, bool show_external);
 
 /*
  * Load the notes tree from each ref listed in 'refs'.  The output is
diff --git a/revision.c b/revision.c
index cd9fcefa0a88..84d9af961988 100644
--- a/revision.c
+++ b/revision.c
@@ -6,6 +6,7 @@
 #include "environment.h"
 #include "gettext.h"
 #include "hex.h"
+#include "notes-external.h"
 #include "object-name.h"
 #include "object-file.h"
 #include "odb.h"
@@ -2583,18 +2584,40 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 	} else if (skip_prefix(arg, "--show-notes=", &optarg) ||
 		   skip_prefix(arg, "--notes=", &optarg)) {
 		if (starts_with(arg, "--show-notes=") &&
-		    revs->notes_opt.use_default_notes < 0)
+		    (revs->notes_opt.use_default_notes < 0 ||
+		     revs->notes_opt.default_notes_suppressed_by_external)) {
 			revs->notes_opt.use_default_notes = 1;
+			revs->notes_opt.default_notes_suppressed_by_external = 0;
+		}
 		enable_ref_display_notes(&revs->notes_opt, &revs->show_notes, optarg);
 		revs->show_notes_given = 1;
 	} else if (!strcmp(arg, "--no-notes")) {
 		disable_display_notes(&revs->notes_opt, &revs->show_notes);
 		revs->show_notes_given = 1;
+	} else if (!strcmp(arg, "--external-notes")) {
+		revs->notes_opt.use_external_notes = 1;
+		revs->show_notes = 1;
+		revs->show_notes_given = 1;
+		/*
+		 * `--external-notes` names a note source on its own. If the
+		 * default notes ref is still undecided, settle it to "off" so
+		 * this option does not also trigger the "no explicit notes
+		 * refs" fallback. A later use of `--notes` or the deprecated
+		 * `--show-notes=<ref>` can still turn the default ref on.
+		 */
+		if (revs->notes_opt.use_default_notes < 0) {
+			revs->notes_opt.use_default_notes = 0;
+			revs->notes_opt.default_notes_suppressed_by_external = 1;
+		}
+	} else if (!strcmp(arg, "--no-external-notes")) {
+		revs->notes_opt.use_external_notes = 0;
 	} else if (!strcmp(arg, "--standard-notes")) {
 		revs->show_notes_given = 1;
 		revs->notes_opt.use_default_notes = 1;
+		revs->notes_opt.default_notes_suppressed_by_external = 0;
 	} else if (!strcmp(arg, "--no-standard-notes")) {
 		revs->notes_opt.use_default_notes = 0;
+		revs->notes_opt.default_notes_suppressed_by_external = 0;
 	} else if (!strcmp(arg, "--oneline")) {
 		revs->verbose_header = 1;
 		get_commit_format("oneline", revs);
@@ -4105,9 +4128,14 @@ static int commit_match(struct commit *commit, struct rev_info *opt)
 
 	/* Append "fake" message parts as needed */
 	if (opt->show_notes) {
+		const struct display_notes_opt *notes_opt = &opt->notes_opt;
+
 		if (!buf.len)
 			strbuf_addstr(&buf, message);
-		format_display_notes(&commit->object.oid, &buf, encoding, true);
+
+		format_display_notes(commit, &buf, encoding, true,
+				     (display_notes_use_external(notes_opt)
+				      && external_notes_for_grep_enabled()));
 	}
 
 	/*
-- 
2.53.0

Re: [PATCH 7/9] notes: support an external command to display notes

[Junio C Hamano]

Siddh Raman Pant <siddh.raman.pant@oracle.com> writes:

> This problem excaberates on scale.
>
> One solution to this is a realtime fetch or faster updation via
> external means, but unfortunately we lose the coherence in the
> display of information, and the user would end up reinventing
> git log.
>
> So let's add support for an external command to display the notes.

It is unclear how we would arrive at "So let's" from the previous
paragraph.  It is not limited to notes but multiple people updating
the same thing racing against each other happens all the time in the
main part of the history, no?  Isn't a better solution for such
racing situation usually based on a better merge support, I have to
wonder?

> We split the addition of documentation and tests from this commit for
> easier review. The new help text added in Documentation/ in the next
> commit should make the usage clear.

It is unclear why a large body of code that is not documented or
whose uses are not illustrated by examples found in the test scripts
is easier to review, though.

[PATCH 8/9] Documentation: document external notes command options

[Siddh Raman Pant]

Assisted-by: Codex:gpt-5.5-xhigh-fast
Signed-off-by: Siddh Raman Pant <siddh.raman.pant@oracle.com>
---
 Documentation/config/notes.adoc        | 57 ++++++++++++++++++++++++++
 Documentation/git-format-patch.adoc    | 11 ++++-
 Documentation/git-range-diff.adoc      |  6 +++
 Documentation/pretty-options.adoc      |  9 ++++
 contrib/completion/git-completion.bash |  4 +-
 5 files changed, 84 insertions(+), 3 deletions(-)

diff --git a/Documentation/config/notes.adoc b/Documentation/config/notes.adoc
index b7e536496f51..b3ef3fa52950 100644
--- a/Documentation/config/notes.adoc
+++ b/Documentation/config/notes.adoc
@@ -34,6 +34,63 @@ The effective value of `core.notesRef` (possibly overridden by
 `GIT_NOTES_REF`) is also implicitly added to the list of refs to be
 displayed.
 
+`notes.externalCommand`::
+	Command to invoke as a long-lived helper when showing commit messages
+	with the `git log` family of commands. Git sends one commit object ID
+	per request on the command's standard input:
++
+------------
+<hex-commit-id>
+------------
++
+For each request, the command must respond on its standard output with either
+`<hex-commit-id> missing` followed by a newline, or `<hex-commit-id> ok <n>`
+followed by a newline and exactly `<n>` bytes of UTF-8 note text followed by a
+newline. The command must respond to each request as it is received; Git does
+not send all commit object IDs before reading responses. Empty note text is not
+displayed. If Git cannot start or communicate with the command, or the command
+sends an invalid response, Git warns once and disables it for the rest of the
+command. External notes are only used while formatting output by default; see
+`notes.externalCommandForGrep` to include them when matching commits.
++
+This setting is only respected in protected configuration (see
+linkgit:git-config[1]). This prevents untrusted repositories from running
+arbitrary commands when notes are displayed.
++
+This setting does not take effect when:
++
+--
+* the value is empty;
+* `--no-notes` is given;
+* `--no-external-notes` is given; or
+* `--notes=<ref>` is given by itself without `--external-notes` or `--notes`.
+--
+
+`notes.externalCommandName`::
+	Name to use in the `Notes (<name>):` header for notes returned by
+	`notes.externalCommand`. Defaults to `external`. This setting is only
+	respected in protected configuration.
+
+`notes.externalCommandTimeoutMs`::
+	Number of milliseconds to wait when reading each response from
+	`notes.externalCommand`. Defaults to `100`. If the command does not
+	produce the expected response in time, Git warns once and disables it
+	for the rest of the command. A value of `0` disables timeout handling,
+	so reads can block until the command writes output or exits. This
+	setting is only	respected in protected configuration.
+
+`notes.externalCommandForGrep`::
+	Boolean indicating whether notes returned by `notes.externalCommand`
+	are included when matching commits with `--grep`, wherever notes would
+	normally participate in grep matching. Defaults to false. This does
+	not make hidden notes searchable in formats such as `--oneline` or
+	`--pretty=%s`; use `--notes` or `--external-notes` if those formats
+	should search notes too. When enabled, revision traversal may invoke
+	the external command for many commits that are not ultimately
+	displayed, which can be expensive for slow commands. The note output
+	can also change which commits match. This setting is only respected in
+	protected configuration.
+
 `notes.rewrite.<command>`::
 	When rewriting commits with _<command>_ (currently `amend` or
 	`rebase`), if this variable is `false`, git will not copy
diff --git a/Documentation/git-format-patch.adoc b/Documentation/git-format-patch.adoc
index 566238245028..472b37e5237a 100644
--- a/Documentation/git-format-patch.adoc
+++ b/Documentation/git-format-patch.adoc
@@ -26,7 +26,7 @@ SYNOPSIS
 		   [--[no-]cover-letter] [--quiet]
 		   [--commit-list-format=<format-spec>]
 		   [--[no-]encode-email-headers]
-		   [--no-notes | --notes[=<ref>]]
+		   [--no-notes | --notes[=<ref>]] [--[no-]external-notes]
 		   [--interdiff=<previous>]
 		   [--range-diff=<previous> [--creation-factor=<percent>]]
 		   [--filename-max-length=<n>]
@@ -395,6 +395,15 @@ configuration options in linkgit:git-notes[1] to use this workflow).
 The default is `--no-notes`, unless the `format.notes` configuration is
 set.
 
+--external-notes::
+--no-external-notes::
+	Invoke or do not invoke `notes.externalCommand` to obtain external
+	notes. Like `--notes=<ref>`, `--external-notes` names an explicit
+	note source and by itself does not include the default notes refs.
+	Use `--external-notes --notes` to include the default notes refs
+	too, or combine `--external-notes` with `--notes=<ref>` to include
+	external notes with specific notes refs.
+
 --signature=<signature>::
 --no-signature::
 	Add a signature to each message produced. Per RFC 3676 the signature
diff --git a/Documentation/git-range-diff.adoc b/Documentation/git-range-diff.adoc
index 5cc5e2ed5673..1de23f300517 100644
--- a/Documentation/git-range-diff.adoc
+++ b/Documentation/git-range-diff.adoc
@@ -12,6 +12,7 @@ git range-diff [--color=[<when>]] [--no-color] [<diff-options>]
 	[--no-dual-color] [--creation-factor=<factor>]
 	[--left-only | --right-only] [--diff-merges=<format>]
 	[--remerge-diff] [--no-notes | --notes[=<ref>]]
+	[--[no-]external-notes]
 	( <range1> <range2> | <rev1>...<rev2> | <base> <rev1> <rev2> )
 	[[--] <path>...]
 
@@ -101,6 +102,11 @@ diff.
 	This flag is passed to the `git log` program
 	(see linkgit:git-log[1]) that generates the patches.
 
+`--external-notes`::
+`--no-external-notes`::
+	This flag is passed to the `git log` program
+	(see linkgit:git-log[1]) that generates the patches.
+
 `<range1> <range2>`::
 	Compare the commits specified by the two ranges, where
 	_<range1>_ is considered an older version of _<range2>_.
diff --git a/Documentation/pretty-options.adoc b/Documentation/pretty-options.adoc
index 658e462b2533..aad851c92cfd 100644
--- a/Documentation/pretty-options.adoc
+++ b/Documentation/pretty-options.adoc
@@ -93,6 +93,15 @@ being displayed. Examples: "`--notes=foo`" will show only notes from
 	"`--notes --notes=foo --no-notes --notes=bar`" will only show notes
 	from `refs/notes/bar`.
 
+`--external-notes`::
+`--no-external-notes`::
+	Invoke or do not invoke `notes.externalCommand` to obtain external
+	notes. Like `--notes=<ref>`, `--external-notes` names an explicit
+	note source and by itself does not include the default notes refs.
+	Use `--external-notes --notes` to include the default notes refs
+	too, or combine `--external-notes` with `--notes=<ref>` to include
+	external notes with specific notes refs.
+
 `--show-notes-by-default`::
 	Show the default notes unless options for displaying specific
 	notes are given.
diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index a8e7c6ddbfb2..146444e65860 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -2023,7 +2023,7 @@ _git_fetch ()
 
 __git_format_patch_extra_options="
 	--full-index --not --all --no-prefix --src-prefix=
-	--dst-prefix= --notes
+	--dst-prefix= --notes --external-notes --no-external-notes
 "
 
 _git_format_patch ()
@@ -2215,7 +2215,7 @@ __git_log_common_options="
 __git_log_gitk_options="
 	--dense --sparse --full-history
 	--simplify-merges --simplify-by-decoration
-	--left-right --notes --no-notes
+	--left-right --notes --no-notes --external-notes --no-external-notes
 "
 # Options that go well for log and shortlog (not gitk)
 __git_log_shortlog_options="
-- 
2.53.0

[PATCH 9/9] t: add tests for external notes command

[Siddh Raman Pant]

Assisted-by: Codex:gpt-5.5-xhigh-fast
Signed-off-by: Siddh Raman Pant <siddh.raman.pant@oracle.com>
---
 t/helper/meson.build                        |   1 +
 t/helper/test-external-notes                |  64 +++
 t/helper/test-notes-external-config-reset.c |  20 +
 t/helper/test-tool.c                        |   1 +
 t/helper/test-tool.h                        |   1 +
 t/lib-notes.sh                              |  19 +
 t/t3206-range-diff.sh                       |  68 +++
 t/t3301-notes.sh                            | 437 ++++++++++++++++++++
 t/t6120-describe.sh                         |  17 +
 9 files changed, 628 insertions(+)
 create mode 100755 t/helper/test-external-notes
 create mode 100644 t/helper/test-notes-external-config-reset.c
 create mode 100644 t/lib-notes.sh

diff --git a/t/helper/meson.build b/t/helper/meson.build
index 675e64c0101b..739614b90e78 100644
--- a/t/helper/meson.build
+++ b/t/helper/meson.build
@@ -35,6 +35,7 @@ test_tool_sources = [
   'test-mergesort.c',
   'test-mktemp.c',
   'test-name-hash.c',
+  'test-notes-external-config-reset.c',
   'test-online-cpus.c',
   'test-pack-deltas.c',
   'test-pack-mtimes.c',
diff --git a/t/helper/test-external-notes b/t/helper/test-external-notes
new file mode 100755
index 000000000000..5e9dde3977ab
--- /dev/null
+++ b/t/helper/test-external-notes
@@ -0,0 +1,64 @@
+#!/bin/sh
+
+prefix=${TEST_EXTERNAL_NOTES_PREFIX:-external-notes}
+response=${TEST_EXTERNAL_NOTES_RESPONSE:-ok}
+line_ending=${TEST_EXTERNAL_NOTES_LINE_ENDING:-lf}
+exit_after_response=${TEST_EXTERNAL_NOTES_EXIT_AFTER_RESPONSE:-}
+exit_delay=${TEST_EXTERNAL_NOTES_EXIT_DELAY:-}
+delay=${TEST_EXTERNAL_NOTES_DELAY:-}
+char_delay=${TEST_EXTERNAL_NOTES_CHAR_DELAY:-}
+ignore_term=${TEST_EXTERNAL_NOTES_IGNORE_TERM:-}
+
+newline='\n'
+case "$line_ending" in
+crlf)
+	newline='\r\n'
+	;;
+none)
+	newline=
+	;;
+esac
+
+echo start >>"$prefix-starts"
+
+test "$ignore_term" = true && trap '' TERM
+
+emit_output() {
+	if test -n "$char_delay"
+	then
+		LC_ALL=C
+		payload=$(printf "$@"; printf .)
+		payload=${payload%.}
+
+		while test -n "$payload"
+		do
+			char=${payload%"${payload#?}"}
+			printf '%s' "$char" || return 1
+			payload=${payload#?}
+			sleep "$char_delay" || return 1
+		done
+	else
+		printf "$@"
+	fi
+}
+
+while IFS= read -r commit; do
+	if test "${TEST_EXTERNAL_NOTES_BODY+x}" = x
+	then
+		note=$TEST_EXTERNAL_NOTES_BODY
+	else
+		note=$commit
+	fi
+	printf "%s\n" "$commit" >>"$prefix-requests"
+	test -z "$delay" || sleep "$delay"
+	if test "$response" = missing
+	then
+		emit_output "%s missing%b" "$commit" "$newline"
+	else
+		emit_output "%s ok %d%b%s%b" \
+			"$commit" "${#note}" "$newline" "$note" "$newline"
+	fi
+	test "$exit_after_response" = true && break
+done
+
+test -z "$exit_delay" || sleep "$exit_delay"
diff --git a/t/helper/test-notes-external-config-reset.c b/t/helper/test-notes-external-config-reset.c
new file mode 100644
index 000000000000..1c6b26e3b49a
--- /dev/null
+++ b/t/helper/test-notes-external-config-reset.c
@@ -0,0 +1,20 @@
+#include "test-tool.h"
+#include "notes-external.h"
+
+int cmd__notes_external_config_reset(int argc, const char **argv UNUSED)
+{
+	if (argc != 1)
+		die("usage: test-tool notes-external-config-reset");
+
+	set_external_notes_command("helper");
+	set_external_notes_command_name("label");
+	set_external_notes_command_timeout_ms(250);
+	set_external_notes_for_grep(1);
+	reset_external_notes_command();
+
+	printf("configured=%d\n", external_notes_command_configured());
+	printf("name=%s\n", external_notes_command_name());
+	printf("timeout_ms=%d\n", external_notes_command_timeout_ms());
+	printf("grep=%d\n", external_notes_for_grep_enabled());
+	return 0;
+}
diff --git a/t/helper/test-tool.c b/t/helper/test-tool.c
index a7abc618b388..31bb2d1dca47 100644
--- a/t/helper/test-tool.c
+++ b/t/helper/test-tool.c
@@ -45,6 +45,7 @@ static struct test_cmd cmds[] = {
 	{ "mergesort", cmd__mergesort },
 	{ "mktemp", cmd__mktemp },
 	{ "name-hash", cmd__name_hash },
+	{ "notes-external-config-reset", cmd__notes_external_config_reset },
 	{ "online-cpus", cmd__online_cpus },
 	{ "pack-deltas", cmd__pack_deltas },
 	{ "pack-mtimes", cmd__pack_mtimes },
diff --git a/t/helper/test-tool.h b/t/helper/test-tool.h
index 7f150fa1eb9a..ff25f0a29cf2 100644
--- a/t/helper/test-tool.h
+++ b/t/helper/test-tool.h
@@ -38,6 +38,7 @@ int cmd__match_trees(int argc, const char **argv);
 int cmd__mergesort(int argc, const char **argv);
 int cmd__mktemp(int argc, const char **argv);
 int cmd__name_hash(int argc, const char **argv);
+int cmd__notes_external_config_reset(int argc, const char **argv);
 int cmd__online_cpus(int argc, const char **argv);
 int cmd__pack_deltas(int argc, const char **argv);
 int cmd__pack_mtimes(int argc, const char **argv);
diff --git a/t/lib-notes.sh b/t/lib-notes.sh
new file mode 100644
index 000000000000..07422540d58f
--- /dev/null
+++ b/t/lib-notes.sh
@@ -0,0 +1,19 @@
+# Helpers for scripts testing notes behavior.
+
+# notes.externalCommand is run through a shell, so quote the path.
+external_notes_command=$(
+	printf "%s\n" "$TEST_DIRECTORY/helper/test-external-notes" |
+	sed "s/'/'\\\\''/g; s/^/'/; s/$/'/"
+)
+
+# The helper above is a shell script. Few Windows CI tests (3 out of 10
+# in matrix) are spending more than the production default timeout just
+# starting the shell and exchanging the first response, so tests that
+# are not about timeout behavior fail. So let us opt into a wider 1s
+# deadline for Windows instead of 100ms.
+external_notes_command_timeout_config=
+if test_have_prereq MINGW
+then
+	_timeout_config="notes.externalCommandTimeoutMs=1000"
+	external_notes_command_timeout_config="-c $_timeout_config"
+fi
diff --git a/t/t3206-range-diff.sh b/t/t3206-range-diff.sh
index 1e812df806bb..96adeb9bc4fe 100755
--- a/t/t3206-range-diff.sh
+++ b/t/t3206-range-diff.sh
@@ -6,6 +6,7 @@ GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
 . ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-notes.sh
 
 # Note that because of the range-diff's heuristics, test_commit does more
 # harm than good.  We need some real history.
@@ -690,6 +691,37 @@ test_expect_success 'range-diff with --notes=custom does not show default notes'
 	grep "## Notes (custom) ##" actual
 '
 
+test_expect_success 'range-diff with --external-notes' '
+	topic_oid=$(git rev-parse topic) &&
+	unmodified_oid=$(git rev-parse unmodified) &&
+	git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		range-diff --no-color --external-notes \
+		main..topic main..unmodified >actual &&
+	test_grep "## Notes (external) ##" actual &&
+	test_grep "^    -    $topic_oid$" actual &&
+	test_grep "^    +    $unmodified_oid$" actual &&
+	! grep "## Notes ##" actual
+'
+
+test_expect_success 'range-diff with disabled external notes' '
+	test_when_finished "git notes remove topic unmodified || :" &&
+	git notes add -m "topic note" topic &&
+	git notes add -m "unmodified note" unmodified &&
+	TEST_EXTERNAL_NOTES_PREFIX=range-diff-external-notes \
+		git -c notes.externalCommand="$external_notes_command" \
+		range-diff --no-color --external-notes --no-external-notes \
+		main..topic main..unmodified >actual &&
+	cat >expect <<-EOF &&
+	1:  $(test_oid t1) = 1:  $(test_oid u1) s/5/A/
+	2:  $(test_oid t2) = 2:  $(test_oid u2) s/4/A/
+	3:  $(test_oid t3) = 3:  $(test_oid u3) s/11/B/
+	4:  $(test_oid t4) = 4:  $(test_oid u4) s/12/B/
+	EOF
+	test_cmp expect actual &&
+	test_path_is_missing range-diff-external-notes-starts
+'
+
 test_expect_success 'format-patch --range-diff does not compare notes by default' '
 	test_when_finished "git notes remove topic unmodified || :" &&
 	git notes add -m "topic note" topic &&
@@ -780,6 +812,42 @@ test_expect_success 'format-patch --range-diff with --notes' '
 	test_cmp expect actual
 '
 
+test_expect_success 'format-patch --range-diff with --external-notes' '
+	topic_oid=$(git rev-parse topic) &&
+	unmodified_oid=$(git rev-parse unmodified) &&
+	test_when_finished "rm -f 000?-*" &&
+	git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		format-patch --external-notes --cover-letter --range-diff=$prev \
+		main..unmodified >actual &&
+	test_line_count = 5 actual &&
+	test_grep "^Range-diff:$" 0000-* &&
+	test_grep "## Notes (external) ##" 0000-* &&
+	test_grep "^    -    $topic_oid$" 0000-* &&
+	test_grep "^    +    $unmodified_oid$" 0000-* &&
+	! grep "## Notes ##" 0000-*
+'
+
+test_expect_success 'format-patch --range-diff with disabled external notes' '
+	test_when_finished "git notes remove topic unmodified || :" &&
+	git notes add -m "topic note" topic &&
+	git notes add -m "unmodified note" unmodified &&
+	test_when_finished "rm -f 000?-*" &&
+	TEST_EXTERNAL_NOTES_PREFIX=range-diff-external-notes \
+		git -c notes.externalCommand="$external_notes_command" \
+		format-patch --external-notes --no-external-notes \
+		--cover-letter --range-diff=$prev main..unmodified >actual &&
+	test_line_count = 5 actual &&
+	test_grep "^Range-diff:$" 0000-* &&
+	grep "= 1: .* s/5/A" 0000-* &&
+	grep "= 2: .* s/4/A" 0000-* &&
+	grep "= 3: .* s/11/B" 0000-* &&
+	grep "= 4: .* s/12/B" 0000-* &&
+	! grep "Notes" 0000-* &&
+	! grep "note" 0000-* &&
+	test_path_is_missing range-diff-external-notes-starts
+'
+
 test_expect_success 'format-patch --range-diff with format.notes config' '
 	test_when_finished "git notes remove topic unmodified || :" &&
 	git notes add -m "topic note" topic &&
diff --git a/t/t3301-notes.sh b/t/t3301-notes.sh
index 27439010dfbc..5a162dff3917 100755
--- a/t/t3301-notes.sh
+++ b/t/t3301-notes.sh
@@ -6,6 +6,7 @@
 test_description='Test commit notes'
 
 . ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-notes.sh
 
 write_script fake_editor <<\EOF
 echo "$MSG" >"$1"
@@ -16,6 +17,11 @@ export GIT_EDITOR
 
 indent="    "
 
+run_with_limited_time () (
+	{ set +x; } 2>/dev/null
+	"$PERL_PATH" -e 'alarm shift; exec @ARGV' -- "$@"
+)
+
 test_expect_success 'cannot annotate non-existing HEAD' '
 	test_must_fail env MSG=3 git notes add
 '
@@ -909,6 +915,437 @@ test_expect_success 'displayed notes are used for grep matching' '
 	test_must_be_empty actual
 '
 
+test_expect_success 'notes.externalCommand shows external notes from protected config' '
+	commit=$(git rev-parse HEAD) &&
+	parent=$(git rev-parse HEAD^) &&
+	rm -f external-notes-starts external-notes-requests &&
+	git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		log -2 >actual &&
+	test_line_count = 1 external-notes-starts &&
+	{
+		printf "%s\n" "$commit" &&
+		printf "%s\n" "$parent"
+	} >expect-requests &&
+	test_cmp expect-requests external-notes-requests &&
+	test_grep "Notes (external):" actual &&
+	test_grep "^    $commit$" actual &&
+	test_grep "^    $parent$" actual
+'
+
+test_expect_success PERL,EXECKEEPSPID 'notes.externalCommand terminates helper during exit cleanup' '
+	commit=$(git rev-parse HEAD) &&
+	test_env TEST_EXTERNAL_NOTES_EXIT_DELAY=10 \
+		run_with_limited_time 2 \
+		git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		log --external-notes -1 >actual &&
+	test_grep "^Notes (external):$" actual &&
+	test_grep "^    $commit$" actual
+'
+
+test_expect_success 'notes.externalCommandName labels external notes' '
+	commit=$(git rev-parse HEAD) &&
+	git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		-c notes.externalCommandName=commit-id log -1 >actual &&
+	test_grep "Notes (commit-id):" actual &&
+	test_grep "^    $commit$" actual
+'
+
+test_expect_success 'notes.externalCommandName is rendered literally' '
+	commit=$(git rev-parse HEAD) &&
+	git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		-c notes.externalCommandName=refs/notes/commits \
+		log --external-notes -1 >actual &&
+	test_grep "^Notes (refs/notes/commits):$" actual &&
+	! grep "^Notes:$" actual &&
+	test_grep "^    $commit$" actual
+'
+
+test_expect_success 'notes.externalCommandTimeoutMs rejects negative values' '
+	test_must_fail git -c notes.externalCommand="$external_notes_command" \
+		-c notes.externalCommandTimeoutMs=-1 log -1 2>err &&
+	test_grep "notes.externalCommandTimeoutMs must be non-negative" err
+'
+
+test_expect_success 'notes.externalCommandTimeoutMs times out delayed response' '
+	git log -1 >expect &&
+	test_env TEST_EXTERNAL_NOTES_DELAY=1 \
+		git -c notes.externalCommand="$external_notes_command" \
+		-c notes.externalCommandTimeoutMs=1 \
+		log -1 >actual 2>err &&
+	test_cmp expect actual &&
+	test_grep "notes.externalCommand failed" err &&
+	test_line_count = 1 err
+'
+
+test_expect_success 'notes.externalCommandTimeoutMs applies to whole response' '
+	git log -1 >expect &&
+	test_env TEST_EXTERNAL_NOTES_BODY=x \
+		 TEST_EXTERNAL_NOTES_CHAR_DELAY=0.02 \
+		git -c notes.externalCommand="$external_notes_command" \
+		-c notes.externalCommandTimeoutMs=50 \
+		log -1 >actual 2>err &&
+	test_cmp expect actual &&
+	test_grep "notes.externalCommand failed" err &&
+	test_line_count = 1 err
+'
+
+test_expect_success PERL,EXECKEEPSPID 'notes.externalCommandTimeoutMs terminates timed-out helper' '
+	git log -1 >expect &&
+	test_env TEST_EXTERNAL_NOTES_DELAY=10 \
+		run_with_limited_time 2 \
+		git -c notes.externalCommand="$external_notes_command" \
+		-c notes.externalCommandTimeoutMs=1 \
+		log -1 >actual 2>err &&
+	test_cmp expect actual &&
+	test_grep "notes.externalCommand failed" err &&
+	test_line_count = 1 err
+'
+
+test_expect_success PERL,EXECKEEPSPID 'notes.externalCommandTimeoutMs force-kills timed-out helper' '
+	git log -1 >expect &&
+	test_env TEST_EXTERNAL_NOTES_DELAY=10 \
+		 TEST_EXTERNAL_NOTES_IGNORE_TERM=true \
+		run_with_limited_time 2 \
+		git -c notes.externalCommand="$external_notes_command" \
+		-c notes.externalCommandTimeoutMs=1 \
+		log -1 >actual 2>err &&
+	test_cmp expect actual &&
+	test_grep "notes.externalCommand failed" err &&
+	test_line_count = 1 err
+'
+
+test_expect_success 'notes.externalCommandTimeoutMs=0 disables timeout' '
+	commit=$(git rev-parse HEAD) &&
+	test_env TEST_EXTERNAL_NOTES_DELAY=1 \
+		git -c notes.externalCommand="$external_notes_command" \
+		-c notes.externalCommandTimeoutMs=0 \
+		log --external-notes -1 >actual &&
+	test_grep "^Notes (external):$" actual &&
+	test_grep "^    $commit$" actual
+'
+
+test_expect_success 'notes.externalCommand handles CRLF note bodies' '
+	body=$(printf "A\r\nB") &&
+	test_env TEST_EXTERNAL_NOTES_BODY="$body" \
+		git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		log --external-notes -1 >actual &&
+	test_grep "^Notes (external):$" actual &&
+	test_grep "^    B$" actual
+'
+
+test_expect_success 'notes.externalCommand accepts CRLF missing response' '
+	git log -1 >expect &&
+	test_env TEST_EXTERNAL_NOTES_RESPONSE=missing \
+		 TEST_EXTERNAL_NOTES_LINE_ENDING=crlf \
+		git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		log -1 >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'notes.externalCommand rejects unterminated missing response' '
+	git log -1 >expect &&
+	test_env TEST_EXTERNAL_NOTES_RESPONSE=missing \
+		 TEST_EXTERNAL_NOTES_LINE_ENDING=none \
+		 TEST_EXTERNAL_NOTES_EXIT_AFTER_RESPONSE=true \
+		git -c notes.externalCommand="$external_notes_command" \
+		log -1 >actual 2>err &&
+	test_cmp expect actual &&
+	test_grep "notes.externalCommand failed" err &&
+	test_line_count = 1 err
+'
+
+test_expect_success PERL,EXECKEEPSPID 'notes.externalCommand rejects unterminated live response without deadlock' '
+	git log -1 >expect &&
+	test_env TEST_EXTERNAL_NOTES_RESPONSE=missing \
+		 TEST_EXTERNAL_NOTES_LINE_ENDING=none \
+		run_with_limited_time 2 \
+		git -c notes.externalCommand="$external_notes_command" \
+		log -1 >actual 2>err &&
+	test_cmp expect actual &&
+	test_grep "notes.externalCommand failed" err &&
+	test_line_count = 1 err
+'
+
+test_expect_success 'notes.externalCommand accepts CRLF protocol lines' '
+	commit=$(git rev-parse HEAD) &&
+	test_env TEST_EXTERNAL_NOTES_LINE_ENDING=crlf \
+		git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		log --external-notes -1 >actual &&
+	test_grep "^Notes (external):$" actual &&
+	test_grep "^    $commit$" actual
+'
+
+test_expect_success 'notes.externalCommand missing response shows no external notes' '
+	write_script external-notes-missing <<-\EOF &&
+	while IFS= read -r commit
+	do
+		printf "%s missing\n" "$commit"
+	done
+	EOF
+	git log -1 >expect &&
+	git -c notes.externalCommand=./external-notes-missing log -1 >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'notes.externalCommand empty note shows no external notes' '
+	write_script external-notes-empty <<-\EOF &&
+	while IFS= read -r commit
+	do
+		printf "%s ok 0\n\n" "$commit"
+	done
+	EOF
+	git log -1 >expect &&
+	git -c notes.externalCommand=./external-notes-empty log -1 >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'notes.externalCommand rejects invalid note lengths' '
+	write_script external-notes-invalid-length <<-\EOF &&
+	while IFS= read -r commit
+	do
+		printf "%s ok %s\n" "$commit" "$1"
+	done
+	EOF
+	git log -2 >expect &&
+	for bad_length in -1 +1 1x x
+	do
+		git -c notes.externalCommand="./external-notes-invalid-length $bad_length" \
+			log -2 >actual 2>err &&
+		test_cmp expect actual &&
+		test_grep "notes.externalCommand failed" err &&
+		test_line_count = 1 err || return 1
+	done
+'
+
+test_expect_success 'notes.externalCommand is suppressed by --no-notes' '
+	rm -f external-notes-starts &&
+	git -c notes.externalCommand="$external_notes_command" log --no-notes -1 >actual &&
+	test_path_is_missing external-notes-starts &&
+	! grep "Notes (external):" actual
+'
+
+test_expect_success 'notes.externalCommand is suppressed by --no-external-notes' '
+	rm -f external-notes-starts &&
+	git log -1 >expect &&
+	git -c notes.externalCommand="$external_notes_command" \
+		log --no-external-notes -1 >actual &&
+	test_cmp expect actual &&
+	test_path_is_missing external-notes-starts
+'
+
+test_expect_success 'notes.externalCommand combines with explicit notes ref' '
+	commit=$(git rev-parse HEAD) &&
+	rm -f external-notes-starts &&
+	git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		log --notes=other --external-notes -1 >actual &&
+	test_line_count = 1 external-notes-starts &&
+	test_grep "Notes (other):" actual &&
+	test_grep "^    other note$" actual &&
+	test_grep "Notes (external):" actual &&
+	test_grep "^    $commit$" actual &&
+	! grep "^    order test$" actual
+'
+
+test_expect_success '--show-notes=ref remains additive after --external-notes' '
+	commit=$(git rev-parse HEAD) &&
+	rm -f external-notes-starts &&
+	git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		log --external-notes --show-notes=other -1 >actual &&
+	test_line_count = 1 external-notes-starts &&
+	test_grep "^Notes:$" actual &&
+	test_grep "^    order test$" actual &&
+	test_grep "^Notes (other):$" actual &&
+	test_grep "^    other note$" actual &&
+	test_grep "^Notes (external):$" actual &&
+	test_grep "^    $commit$" actual
+'
+
+test_expect_success 'notes.externalCommand can be enabled without default notes refs' '
+	commit=$(git rev-parse HEAD) &&
+	rm -f external-notes-starts &&
+	git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		log --external-notes -1 >actual &&
+	test_line_count = 1 external-notes-starts &&
+	test_grep "Notes (external):" actual &&
+	test_grep "^    $commit$" actual &&
+	! grep "^    order test$" actual &&
+	! grep "^    other note$" actual
+'
+
+test_expect_success 'notes.externalCommand combines with default notes refs' '
+	commit=$(git rev-parse HEAD) &&
+	rm -f external-notes-starts &&
+	git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		log --external-notes --notes -1 >actual &&
+	test_line_count = 1 external-notes-starts &&
+	test_grep "Notes:" actual &&
+	test_grep "^    order test$" actual &&
+	test_grep "Notes (external):" actual &&
+	test_grep "^    $commit$" actual &&
+	! grep "^    other note$" actual
+'
+
+test_expect_success 'notes.externalCommand obeys last --external-notes option' '
+	commit=$(git rev-parse HEAD) &&
+	rm -f external-notes-starts &&
+	git log --no-notes -1 >expect &&
+	git -c notes.externalCommand="$external_notes_command" \
+		log --external-notes --no-external-notes -1 >actual &&
+	test_cmp expect actual &&
+	test_path_is_missing external-notes-starts &&
+	git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		log --notes=other --no-external-notes --external-notes -1 >actual &&
+	test_line_count = 1 external-notes-starts &&
+	test_grep "Notes (other):" actual &&
+	test_grep "^    other note$" actual &&
+	test_grep "Notes (external):" actual &&
+	test_grep "^    $commit$" actual &&
+	! grep "^    order test$" actual
+'
+
+test_expect_success 'notes.externalCommand honors raw notes formatting' '
+	commit=$(git rev-parse HEAD) &&
+	git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		show -s --format=%N >actual &&
+	test_grep "^$commit$" actual &&
+	! grep "Notes (external):" actual
+'
+
+test_expect_success 'format-patch --external-notes includes external notes only' '
+	commit=$(git rev-parse HEAD) &&
+	rm -f external-notes-starts &&
+	git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		format-patch --external-notes -1 --stdout >actual &&
+	test_line_count = 1 external-notes-starts &&
+	test_grep "^Notes (external):" actual &&
+	test_grep "^    $commit$" actual &&
+	! grep "^    order test$" actual
+'
+
+test_expect_success 'notes.externalCommand is not used for grep matching' '
+	commit=$(git rev-parse HEAD) &&
+	rm -f external-notes-starts &&
+	git -c notes.externalCommand="$external_notes_command" \
+		log --grep="$commit" >actual &&
+	test_must_be_empty actual &&
+	test_path_is_missing external-notes-starts
+'
+
+test_expect_success 'notes.externalCommandForGrep includes external notes in grep matching' '
+	commit=$(git rev-parse HEAD) &&
+	rm -f external-notes-starts &&
+	git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		-c notes.externalCommandForGrep=true \
+		log --grep="$commit" -1 >actual &&
+	test_line_count = 1 external-notes-starts &&
+	test_grep "Notes (external):" actual
+'
+
+test_expect_success 'notes.externalCommandForGrep does not search hidden notes' '
+	commit=$(git rev-parse HEAD) &&
+	rm -f external-notes-starts &&
+	git -c notes.externalCommand="$external_notes_command" \
+		-c notes.externalCommandForGrep=true \
+		log --oneline --grep="$commit" -1 >actual &&
+	test_must_be_empty actual &&
+	test_path_is_missing external-notes-starts
+'
+
+test_expect_success 'notes.externalCommandForGrep honors --no-external-notes' '
+	commit=$(git rev-parse HEAD) &&
+	rm -f external-notes-starts &&
+	git -c notes.externalCommand="$external_notes_command" \
+		-c notes.externalCommandForGrep=true \
+		log --no-external-notes --grep="$commit" -1 >actual &&
+	test_must_be_empty actual &&
+	test_path_is_missing external-notes-starts
+'
+
+test_expect_success 'notes.externalCommandForGrep combines with explicit notes ref' '
+	commit=$(git rev-parse HEAD) &&
+	rm -f external-notes-starts &&
+	git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		-c notes.externalCommandForGrep=true \
+		log --notes=other --external-notes --grep="$commit" -1 >actual &&
+	test_line_count = 1 external-notes-starts &&
+	test_grep "Notes (external):" actual &&
+	test_grep "Notes (other):" actual &&
+	! grep "^    order test$" actual
+'
+
+test_expect_success 'notes.externalCommandForGrep is ignored from local config' '
+	commit=$(git rev-parse HEAD) &&
+	rm -f external-notes-starts &&
+	test_config notes.externalCommandForGrep true &&
+	git -c notes.externalCommand="$external_notes_command" \
+		log --grep="$commit" >actual &&
+	test_must_be_empty actual &&
+	test_path_is_missing external-notes-starts
+'
+
+test_expect_success 'notes.externalCommand is not used with explicit notes ref' '
+	rm -f external-notes-starts &&
+	git -c notes.externalCommand="$external_notes_command" log --notes=other -1 >actual &&
+	test_path_is_missing external-notes-starts &&
+	! grep "Notes (external):" actual
+'
+
+test_expect_success 'notes.externalCommand is ignored from local config' '
+	rm -f external-notes-starts &&
+	test_config notes.externalCommand "$external_notes_command" &&
+	git log -1 >actual &&
+	test_path_is_missing external-notes-starts &&
+	! grep "Notes (external):" actual
+'
+
+test_expect_success 'notes.externalCommandName is ignored from local config' '
+	test_config notes.externalCommandName local &&
+	git -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		log -1 >actual &&
+	test_grep "Notes (external):" actual &&
+	! grep "Notes (local):" actual
+'
+
+test_expect_success 'reset_external_notes_command clears cached helper config' '
+	test-tool notes-external-config-reset >actual &&
+	cat >expect <<-\EOF &&
+	configured=0
+	name=external
+	timeout_ms=100
+	grep=0
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'notes.externalCommand warning is shown once' '
+	write_script external-notes-fail <<-\EOF &&
+	while IFS= read -r commit
+	do
+		printf "%s-mismatch missing\n" "$commit"
+	done
+	EOF
+	git -c notes.externalCommand=./external-notes-fail log -2 >actual 2>err &&
+	test_grep "notes.externalCommand failed" err &&
+	test_line_count = 1 err
+'
+
 test_expect_success 'Allow notes on non-commits (trees, blobs, tags)' '
 	test_config core.notesRef refs/notes/other &&
 	echo "Note on a tree" >expect &&
diff --git a/t/t6120-describe.sh b/t/t6120-describe.sh
index 8ee3d2c37d02..abbdb42dc9f7 100755
--- a/t/t6120-describe.sh
+++ b/t/t6120-describe.sh
@@ -15,6 +15,7 @@ GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
 . ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-notes.sh
 
 check_describe () {
 	indir= &&
@@ -867,6 +868,22 @@ test_expect_success 'format-rev with %N (note)' '
 	test_cmp expect actual
 '
 
+test_expect_success 'format-rev with %N uses external notes' '
+	commit=$(git -C repo-format rev-parse HEAD) &&
+	rm -f repo-format/format-rev-external-notes-starts \
+		repo-format/format-rev-external-notes-requests &&
+	printf "%s\n" "$commit" >input &&
+	printf "%s\n\n" "$commit" >expect &&
+	TEST_EXTERNAL_NOTES_PREFIX=format-rev-external-notes \
+	git -C repo-format -c notes.externalCommand="$external_notes_command" \
+		$external_notes_command_timeout_config \
+		format-rev --stdin-mode=text --format="tformat:%N" \
+		<input >actual &&
+	test_line_count = 1 repo-format/format-rev-external-notes-starts &&
+	test_cmp input repo-format/format-rev-external-notes-requests &&
+	test_cmp expect actual
+'
+
 test_expect_success 'format-rev --notes<ref> (custom notes ref)' '
 	# One custom notes ref
 	test_when_finished "git -C repo-format notes remove" &&
-- 
2.53.0