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

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>
Message-Id: <20200626201900.8876-1-msmarduch@digitalocean.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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

qemu-options.hx

@@ -4303,16 +4303,22 @@ 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,

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 */ }
     },
 };
@@ -1114,6 +1120,7 @@ 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);
 }
 
 
@@ -3592,6 +3599,8 @@ 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) {

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) {