backup: Store error message for failed backups

If a backup job fails midway it's hard to figure out what happened as
it's running asynchronous. Use the VIR_DOMAIN_JOB_ERRMSG job statistics
field to pass through the error from the first failed backup-blockjob
so that both the consumer of the virDomainGetJobStats and the
corresponding event can see the error.

event 'job-completed' for domain backup-test:
	operation: 9
	time_elapsed: 46
	disk_total: 104857600
	disk_processed: 10158080
	disk_remaining: 94699520
	success: 0
	errmsg: No space left on device

virsh domjobinfo backup-test --completed --anystats
Job type:         Failed
Operation:        Backup
Time elapsed:     46           ms
File processed:   9.688 MiB
File remaining:   90.312 MiB
File total:       100.000 MiB
Error message:    No space left on device

https://bugzilla.redhat.com/show_bug.cgi?id=1812827

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

src/conf/backup_conf.c

@@ -65,6 +65,7 @@ virDomainBackupDefFree(virDomainBackupDefPtr def)
         return;
 
     g_free(def->incremental);
+    g_free(def->errmsg);
     virStorageNetHostDefFree(1, def->server);
 
     for (i = 0; i < def->ndisks; i++) {

src/conf/backup_conf.h

@@ -79,6 +79,8 @@ struct _virDomainBackupDef {
     unsigned long long push_total;
     unsigned long long pull_tmp_used;
     unsigned long long pull_tmp_total;
+
+    char *errmsg; /* error message of failed sub-blockjob */
 };
 
 typedef enum {

src/qemu/qemu_backup.c

@@ -650,6 +650,7 @@ qemuBackupJobTerminate(virDomainObjPtr vm,
     priv->job.completed->stats.backup.tmp_total = priv->backup->pull_tmp_total;
 
     priv->job.completed->status = jobstatus;
+    priv->job.completed->errmsg = g_strdup(priv->backup->errmsg);
 
     qemuDomainEventEmitJobCompleted(priv->driver, vm);
 
@@ -951,6 +952,7 @@ void
 qemuBackupNotifyBlockjobEnd(virDomainObjPtr vm,
                             virDomainDiskDefPtr disk,
                             qemuBlockjobState state,
+                            const char *errmsg,
                             unsigned long long cur,
                             unsigned long long end,
                             int asyncJob)
@@ -964,8 +966,8 @@ qemuBackupNotifyBlockjobEnd(virDomainObjPtr vm,
     virDomainBackupDefPtr backup = priv->backup;
     size_t i;
 
-    VIR_DEBUG("vm: '%s', disk:'%s', state:'%d'",
-              vm->def->name, disk->dst, state);
+    VIR_DEBUG("vm: '%s', disk:'%s', state:'%d' errmsg:'%s'",
+              vm->def->name, disk->dst, state, NULLSTR(errmsg));
 
     if (!backup)
         return;
@@ -985,6 +987,10 @@ qemuBackupNotifyBlockjobEnd(virDomainObjPtr vm,
         backup->push_total += end;
     }
 
+    /* record first error message */
+    if (!backup->errmsg)
+        backup->errmsg = g_strdup(errmsg);
+
     for (i = 0; i < backup->ndisks; i++) {
         virDomainBackupDiskDefPtr backupdisk = backup->disks + i;
 

src/qemu/qemu_backup.h

@@ -38,6 +38,7 @@ void
 qemuBackupNotifyBlockjobEnd(virDomainObjPtr vm,
                             virDomainDiskDefPtr disk,
                             qemuBlockjobState state,
+                            const char *errmsg,
                             unsigned long long cur,
                             unsigned long long end,
                             int asyncJob);

src/qemu/qemu_blockjob.c

@@ -1435,7 +1435,7 @@ qemuBlockJobProcessEventConcludedBackup(virQEMUDriverPtr driver,
     g_autoptr(qemuBlockStorageSourceAttachData) backend = NULL;
     g_autoptr(virJSONValue) actions = NULL;
 
-    qemuBackupNotifyBlockjobEnd(vm, job->disk, newstate,
+    qemuBackupNotifyBlockjobEnd(vm, job->disk, newstate, job->errmsg,
                                 progressCurrent, progressTotal, asyncJob);
 
     if (job->data.backup.store &&

src/qemu/qemu_domain.c

@@ -836,6 +836,10 @@ qemuDomainBackupJobInfoToParams(qemuDomainJobInfoPtr jobInfo,
                                     VIR_DOMAIN_JOB_SUCCESS) < 0)
         return -1;
 
+    if (jobInfo->errmsg &&
+        virTypedParamListAddString(par, jobInfo->errmsg, VIR_DOMAIN_JOB_ERRMSG) < 0)
+        return -1;
+
     *nparams = virTypedParamListStealParams(par, params);
     *type = qemuDomainJobStatusToType(jobInfo->status);
     return 0;