[PATCH] util/qemu-error: prepend guest name to error message to identify affected VM owner

[Mario Smarduch <msmarduch@digitalocean.com>]

This is followup patch to the one submitted back in Oct, 19

https://lists.gnu.org/archive/html/qemu-devel/2019-10/msg02102.html

My mistake here, I took my eyes of the mailing list after I got the
initial thumbs up. This patch follows up on Markus comments in the
above link.

Purpose of this patch:

We want to print guest name for errors, warnings and info messages. This 
was the first of two patches the second being MCE errors targeting a VM 
with guest name prepended. But in a large fleet we see many other
errors that disable a VM or crash it. In a large fleet and centralized
logging having the guest name enables identify of owner and customer.

Signed-off-by: Mario Smarduch <msmarduch@digitalocean.com>
---
Test verification summary:

a) qemu-system-x86_64 -msg help
  guest-name=<bool (on/off)> - Prepends guest name for error messages but only if -name <guestname> is set otherwise option is ignored

  timestamp=<bool (on/off)>

b) qemu-system-x86_64 -help
-msg [timestamp[=on|off]][,guest-name=[on|off]]
                control error message format
                timestamp=on enables timestamps (default: off)
                guest-name=on enables guest name prefix but only if
                              -name guest option is set (default: off)

c) man qemu
       -msg [timestamp[=on|off]][,guest-name[=on|off]]
              Control error message format.

              timestamp=on|off
                     Prefix messages with a timestamp. Default is off.

              guest-name=on|off
                     Prefix  messages  with guest name but only if -name guest
                     option is set otherwise the option is ignored. Default is
                     off.
d) command options
./x86_64-softmmu/qemu-system-x86_64 -msg timestamp
2020-06-26T01:01:23.140294Z qemu-system-x86_64: Testing ERROR...

./x86_64-softmmu/qemu-system-x86_64 -msg timestamp,guest-name
2020-06-26T01:02:30.301431Z qemu-system-x86_64: Testing ERROR...

./x86_64-softmmu/qemu-system-x86_64 -msg timestamp,guest-name \
                                    -name guest=DROPLET-123
2020-06-26T01:04:37.720380Z DROPLET-1234 qemu-system-x86_64: Testing ERROR...

./x86_64-softmmu/qemu-system-x86_64 -msg timestamp=off,guest-name=off \
                                    -name guest=DROPLET-123
qemu-system-x86_64: Testing ERROR...

./x86_64-softmmu/qemu-system-x86_64 -msg timestamp=on,guest-name=off \
                                    -name guest=DROPLET-123
2020-06-26T01:06:33.888859Z qemu-system-x86_64: Testing ERROR...

./x86_64-softmmu/qemu-system-x86_64 -msg timestamp=off,guest-name=on \
                                    -name guest=DROPLET-123
DROPLET-1234 qemu-system-x86_64: Testing ERROR...

./x86_64-softmmu/qemu-system-x86_64 -msg timestamp=on,guest-name=on \
                                    -name guest=DROPLET-123
2020-06-26T01:09:31.116283Z DROPLET-1234 qemu-system-x86_64: Testing ERROR... 


 include/qemu/error-report.h |  2 ++
 qemu-options.hx             | 12 +++++++++---
 softmmu/vl.c                |  9 +++++++++
 util/qemu-error.c           |  7 +++++++
 4 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/include/qemu/error-report.h b/include/qemu/error-report.h
index 87532d8596..a5ad95ff1b 100644
--- a/include/qemu/error-report.h
+++ b/include/qemu/error-report.h
@@ -75,5 +75,7 @@ void error_init(const char *argv0);
 const char *error_get_progname(void);
 
 extern bool error_with_timestamp;
+extern bool error_with_guestname;
+extern const char *error_guest_name;
 
 #endif
diff --git a/qemu-options.hx b/qemu-options.hx
index 93bde2bbc8..ff75510b7c 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4290,16 +4290,22 @@ HXCOMM Deprecated by -accel tcg
 DEF("no-kvm", 0, QEMU_OPTION_no_kvm, "", QEMU_ARCH_I386)
 
 DEF("msg", HAS_ARG, QEMU_OPTION_msg,
-    "-msg timestamp[=on|off]\n"
+    "-msg [timestamp[=on|off]][,guest-name=[on|off]]\n"
     "                control error message format\n"
-    "                timestamp=on enables timestamps (default: off)\n",
+    "                timestamp=on enables timestamps (default: off)\n"
+    "                guest-name=on enables guest name prefix but only if\n"
+    "                              -name guest option is set (default: off)\n",
     QEMU_ARCH_ALL)
 SRST
-``-msg timestamp[=on|off]``
+``-msg [timestamp[=on|off]][,guest-name[=on|off]]``
     Control error message format.
 
     ``timestamp=on|off``
         Prefix messages with a timestamp. Default is off.
+
+    ``guest-name=on|off``
+        Prefix messages with guest name but only if -name guest option is set
+        otherwise the option is ignored. Default is off.
 ERST
 
 DEF("dump-vmstate", HAS_ARG, QEMU_OPTION_dump_vmstate,
diff --git a/softmmu/vl.c b/softmmu/vl.c
index f669c06ede..3f7aad89c3 100644
--- a/softmmu/vl.c
+++ b/softmmu/vl.c
@@ -389,6 +389,12 @@ static QemuOptsList qemu_msg_opts = {
             .name = "timestamp",
             .type = QEMU_OPT_BOOL,
         },
+        {
+            .name = "guest-name",
+            .type = QEMU_OPT_BOOL,
+            .help = "Prepends guest name for error messages but only if "
+                    "-name guest is set otherwise option is ignored\n",
+        },
         { /* end of list */ }
     },
 };
@@ -1109,6 +1115,7 @@ static void realtime_init(void)
 static void configure_msg(QemuOpts *opts)
 {
     error_with_timestamp = qemu_opt_get_bool(opts, "timestamp", false);
+    error_with_guestname = qemu_opt_get_bool(opts, "guest-name", false);
 }
 
 
@@ -3578,6 +3585,8 @@ void qemu_init(int argc, char **argv, char **envp)
                 if (!opts) {
                     exit(1);
                 }
+                /* Capture guest name if -msg guest-name is used later */
+                error_guest_name = qemu_opt_get(opts, "guest");
                 break;
             case QEMU_OPTION_prom_env:
                 if (nb_prom_envs >= MAX_PROM_ENVS) {
diff --git a/util/qemu-error.c b/util/qemu-error.c
index dac7c7dc50..017288b6c9 100644
--- a/util/qemu-error.c
+++ b/util/qemu-error.c
@@ -26,6 +26,8 @@ typedef enum {
 
 /* Prepend timestamp to messages */
 bool error_with_timestamp;
+bool error_with_guestname;
+const char *error_guest_name;
 
 int error_printf(const char *fmt, ...)
 {
@@ -213,6 +215,11 @@ static void vreport(report_type type, const char *fmt, va_list ap)
         g_free(timestr);
     }
 
+    /* Only prepend guest name if -msg guest-name and -name guest=... are set */
+    if (error_with_guestname && error_guest_name && !cur_mon) {
+        error_printf("%s ", error_guest_name);
+    }
+
     print_loc();
 
     switch (type) {
-- 
2.17.1