[PATCH v4 09/11] odb/transaction: introduce ODB transaction flags

[Justin Tobler <jltobler@gmail.com>]

The temporary directory used by git-receive-pack(1) to write objects is
managed slightly differently than how it is done via ODB transactions:

  - The temporary directory is eagerly created upfront, instead of
    waiting for the first object write.

  - The prefix name of the temporary directory is "incoming" instead of
    "bulk-fsync".

In a subsequent commit, git-receive-pack(1) will use ODB transactions
instead of `tmp_objdir` directly. To provide a means to configure the
same transaction behavior, introduce `enum odb_transaction_flags` and
the ODB_TRANSACTION_RECEIVE flag intended as a signal for ODB
transactions using the "files" backend to be set up for
git-receive-pack(1). Transaction call sites are updated accordingly to
provide the required flag parameter.

Signed-off-by: Justin Tobler <jltobler@gmail.com>
---
 builtin/add.c            |  2 +-
 builtin/unpack-objects.c |  2 +-
 builtin/update-index.c   |  2 +-
 cache-tree.c             |  2 +-
 object-file.c            | 29 ++++++++++++++++++++++++++---
 object-file.h            |  4 +++-
 odb/source-files.c       |  5 +++--
 odb/source-inmemory.c    |  3 ++-
 odb/source-loose.c       |  3 ++-
 odb/source.h             |  9 ++++++---
 odb/transaction.c        |  5 +++--
 odb/transaction.h        | 15 +++++++++++----
 read-cache.c             |  2 +-
 13 files changed, 61 insertions(+), 22 deletions(-)

diff --git a/builtin/add.c b/builtin/add.c
index 3d5d9cfdb9..60ffbede2b 100644
--- a/builtin/add.c
+++ b/builtin/add.c
@@ -581,7 +581,7 @@ int cmd_add(int argc,
 		string_list_clear(&only_match_skip_worktree, 0);
 	}
 
-	odb_transaction_begin_or_die(repo->objects, &transaction);
+	odb_transaction_begin_or_die(repo->objects, &transaction, 0);
 
 	ps_matched = xcalloc(pathspec.nr, 1);
 	if (add_renormalize)
diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c
index d0136cdd99..c3d0fc7507 100644
--- a/builtin/unpack-objects.c
+++ b/builtin/unpack-objects.c
@@ -598,7 +598,7 @@ static void unpack_all(void)
 		progress = start_progress(the_repository,
 					  _("Unpacking objects"), nr_objects);
 	CALLOC_ARRAY(obj_list, nr_objects);
-	odb_transaction_begin_or_die(the_repository->objects, &transaction);
+	odb_transaction_begin_or_die(the_repository->objects, &transaction, 0);
 	for (i = 0; i < nr_objects; i++) {
 		unpack_one(i);
 		display_progress(progress, i + 1);
diff --git a/builtin/update-index.c b/builtin/update-index.c
index 17f3ea284c..bf6ea60ef4 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -1124,7 +1124,7 @@ int cmd_update_index(int argc,
 	 * Allow the object layer to optimize adding multiple objects in
 	 * a batch.
 	 */
-	odb_transaction_begin_or_die(the_repository->objects, &transaction);
+	odb_transaction_begin_or_die(the_repository->objects, &transaction, 0);
 	while (ctx.argc) {
 		if (parseopt_state != PARSE_OPT_DONE)
 			parseopt_state = parse_options_step(&ctx, options,
diff --git a/cache-tree.c b/cache-tree.c
index 8eec1d4d52..99c6a0a7d0 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -492,7 +492,7 @@ int cache_tree_update(struct index_state *istate, int flags)
 	trace_performance_enter();
 	trace2_region_enter("cache_tree", "update", istate->repo);
 	if (!inflight)
-		odb_transaction_begin_or_die(the_repository->objects, &transaction);
+		odb_transaction_begin_or_die(the_repository->objects, &transaction, 0);
 	i = update_one(istate->cache_tree, istate->cache, istate->cache_nr,
 		       "", 0, &skip, flags);
 	if (!inflight)
diff --git a/object-file.c b/object-file.c
index 39b92e275c..0640a22009 100644
--- a/object-file.c
+++ b/object-file.c
@@ -498,6 +498,7 @@ struct odb_transaction_files {
 
 	struct tmp_objdir *objdir;
 	struct transaction_packfile packfile;
+	const char *prefix;
 };
 
 static int odb_transaction_files_prepare(struct odb_transaction *base)
@@ -514,7 +515,7 @@ static int odb_transaction_files_prepare(struct odb_transaction *base)
 	if (!transaction || transaction->objdir)
 		return 0;
 
-	transaction->objdir = tmp_objdir_create(base->source->odb->repo, "bulk-fsync");
+	transaction->objdir = tmp_objdir_create(base->source->odb->repo, transaction->prefix);
 	if (!transaction->objdir)
 		return error(_("unable to create temporary object directory"));
 
@@ -1359,7 +1360,7 @@ int index_fd(struct index_state *istate, struct object_id *oid,
 			int inflight = !!transaction;
 
 			if (!inflight)
-				odb_transaction_begin_or_die(odb, &transaction);
+				odb_transaction_begin_or_die(odb, &transaction, 0);
 			ret = odb_transaction_write_object_stream(transaction,
 								  &stream,
 								  xsize_t(st->st_size),
@@ -1703,7 +1704,8 @@ static int odb_transaction_files_env(struct odb_transaction *base,
 }
 
 int odb_transaction_files_begin(struct odb_source *source,
-				struct odb_transaction **out)
+				struct odb_transaction **out,
+				enum odb_transaction_flags flags)
 {
 	struct odb_transaction_files *transaction;
 
@@ -1712,6 +1714,27 @@ int odb_transaction_files_begin(struct odb_source *source,
 	transaction->base.commit = odb_transaction_files_commit;
 	transaction->base.write_object_stream = odb_transaction_files_write_object_stream;
 	transaction->base.env = odb_transaction_files_env;
+
+	transaction->prefix = "bulk-fsync";
+	if (flags & ODB_TRANSACTION_RECEIVE) {
+		/*
+		 * ODB transactions for git-receive-pack(1) eagerly create a
+		 * temporary directory and use a different temporary directory
+		 * prefix.
+		 *
+		 * NEEDSWORK: This transaction flag is only used by the "files"
+		 * backend to special case temporary directory set up and
+		 * handling. Ideally transaction users should not have to care
+		 * though. To avoid this, we could eagerly create the temporary
+		 * directory and use the same prefix name for all transactions.
+		 */
+		transaction->prefix = "incoming";
+		if (odb_transaction_files_prepare(&transaction->base)) {
+			free(transaction);
+			return -1;
+		}
+	}
+
 	*out = &transaction->base;
 
 	return 0;
diff --git a/object-file.h b/object-file.h
index 1a023226ac..bdd2d67a2e 100644
--- a/object-file.h
+++ b/object-file.h
@@ -5,6 +5,7 @@
 #include "object.h"
 #include "odb.h"
 #include "odb/source-loose.h"
+#include "odb/transaction.h"
 
 /* The maximum size for an object header. */
 #define MAX_HEADER_LEN 32
@@ -197,6 +198,7 @@ struct odb_transaction;
  * to make new objects visible.
  */
 int odb_transaction_files_begin(struct odb_source *source,
-				struct odb_transaction **out);
+				struct odb_transaction **out,
+				enum odb_transaction_flags flags);
 
 #endif /* OBJECT_FILE_H */
diff --git a/odb/source-files.c b/odb/source-files.c
index 2545bd81d4..534f48aad9 100644
--- a/odb/source-files.c
+++ b/odb/source-files.c
@@ -180,9 +180,10 @@ static int odb_source_files_write_object_stream(struct odb_source *source,
 }
 
 static int odb_source_files_begin_transaction(struct odb_source *source,
-					      struct odb_transaction **out)
+					      struct odb_transaction **out,
+					      enum odb_transaction_flags flags)
 {
-	return odb_transaction_files_begin(source, out);
+	return odb_transaction_files_begin(source, out, flags);
 }
 
 static int odb_source_files_read_alternates(struct odb_source *source,
diff --git a/odb/source-inmemory.c b/odb/source-inmemory.c
index e004566d76..9644d9d474 100644
--- a/odb/source-inmemory.c
+++ b/odb/source-inmemory.c
@@ -304,7 +304,8 @@ static int odb_source_inmemory_freshen_object(struct odb_source *source,
 }
 
 static int odb_source_inmemory_begin_transaction(struct odb_source *source UNUSED,
-						 struct odb_transaction **out UNUSED)
+						 struct odb_transaction **out UNUSED,
+						 enum odb_transaction_flags flags UNUSED)
 {
 	return error("in-memory source does not support transactions");
 }
diff --git a/odb/source-loose.c b/odb/source-loose.c
index 66e6bb8d3f..57c91986b4 100644
--- a/odb/source-loose.c
+++ b/odb/source-loose.c
@@ -638,7 +638,8 @@ static int odb_source_loose_write_object_stream(struct odb_source *source,
 }
 
 static int odb_source_loose_begin_transaction(struct odb_source *source UNUSED,
-					      struct odb_transaction **out UNUSED)
+					      struct odb_transaction **out UNUSED,
+					      enum odb_transaction_flags flags UNUSED)
 {
 	/* TODO: this is a known omission that we'll want to address eventually. */
 	return error("loose source does not support transactions");
diff --git a/odb/source.h b/odb/source.h
index 2192a101b8..3790d03ff2 100644
--- a/odb/source.h
+++ b/odb/source.h
@@ -3,6 +3,7 @@
 
 #include "object.h"
 #include "odb.h"
+#include "odb/transaction.h"
 
 enum odb_source_type {
 	/*
@@ -228,7 +229,8 @@ struct odb_source {
 	 * negative error code otherwise.
 	 */
 	int (*begin_transaction)(struct odb_source *source,
-				 struct odb_transaction **out);
+				 struct odb_transaction **out,
+				 enum odb_transaction_flags flags);
 
 	/*
 	 * This callback is expected to read the list of alternate object
@@ -467,9 +469,10 @@ static inline int odb_source_write_alternate(struct odb_source *source,
  * Returns 0 on success, a negative error code otherwise.
  */
 static inline int odb_source_begin_transaction(struct odb_source *source,
-					       struct odb_transaction **out)
+					       struct odb_transaction **out,
+					       enum odb_transaction_flags flags)
 {
-	return source->begin_transaction(source, out);
+	return source->begin_transaction(source, out, flags);
 }
 
 #endif
diff --git a/odb/transaction.c b/odb/transaction.c
index 92ec8786a1..dab7da6a9a 100644
--- a/odb/transaction.c
+++ b/odb/transaction.c
@@ -4,14 +4,15 @@
 #include "odb/transaction.h"
 
 int odb_transaction_begin(struct object_database *odb,
-			  struct odb_transaction **out)
+			  struct odb_transaction **out,
+			  enum odb_transaction_flags flags)
 {
 	int ret;
 
 	if (odb->transaction)
 		return error(_("object database transaction already pending"));
 
-	ret = odb_source_begin_transaction(odb->sources, out);
+	ret = odb_source_begin_transaction(odb->sources, out, flags);
 	if (!ret)
 		odb->transaction = *out;
 
diff --git a/odb/transaction.h b/odb/transaction.h
index 5e51ce5ca4..4cb2eafcbf 100644
--- a/odb/transaction.h
+++ b/odb/transaction.h
@@ -3,7 +3,6 @@
 
 #include "gettext.h"
 #include "odb.h"
-#include "odb/source.h"
 
 /*
  * A transaction may be started for an object database prior to writing new
@@ -44,6 +43,12 @@ struct odb_transaction {
 	int (*env)(struct odb_transaction *transaction, struct strvec *env);
 };
 
+/* Flags used to configure an ODB transaction. */
+enum odb_transaction_flags {
+	/* Configures the transaction for use with git-receive-pack(1). */
+	ODB_TRANSACTION_RECEIVE = (1 << 0),
+};
+
 /*
  * Starts an ODB transaction and returns it via `out`. Subsequent objects are
  * written to the transaction and not committed until odb_transaction_commit()
@@ -52,12 +57,14 @@ struct odb_transaction {
  * ODB already has an inflight transaction pending.
  */
 int odb_transaction_begin(struct object_database *odb,
-			  struct odb_transaction **out);
+			  struct odb_transaction **out,
+			  enum odb_transaction_flags flags);
 
 static inline void odb_transaction_begin_or_die(struct object_database *odb,
-						struct odb_transaction **out)
+						struct odb_transaction **out,
+						enum odb_transaction_flags flags)
 {
-	if (odb_transaction_begin(odb, out))
+	if (odb_transaction_begin(odb, out, flags))
 		die(_("failed to start ODB transaction"));
 }
 
diff --git a/read-cache.c b/read-cache.c
index d511d25834..50e2320c8d 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -4044,7 +4044,7 @@ int add_files_to_cache(struct repository *repo, const char *prefix,
 	 * may not have their own transaction active.
 	 */
 	if (!inflight)
-		odb_transaction_begin_or_die(repo->objects, &transaction);
+		odb_transaction_begin_or_die(repo->objects, &transaction, 0);
 	run_diff_files(&rev, DIFF_RACY_IS_MODIFIED);
 	if (!inflight)
 		odb_transaction_commit(transaction);
-- 
2.55.0.122.gf85a7e6620