[pve-devel] [RFC qemu 7/7] block/backup: set callback for cbw errors

[Fiona Ebner <f.ebner@proxmox.com>]

The callback is invoked when cbw is configured to not break the guest
write and will abort a backup job immediately. Currently the backup
has to wait for the rest of the block copy operation to finish before
checking the cbw error state.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---

Note for testers: if e.g. the PBS is compeletly unreachable, the
backup job still will need to wait until the in-flight request is
aborted after 15 minutes. But the guest writes should be fast again.

 block/backup.c | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/block/backup.c b/block/backup.c
index ba153110d3..43d34ce4c2 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -32,6 +32,45 @@
 
 static const BlockJobDriver backup_job_driver;
 
+typedef struct {
+    Job *job;
+    int ret;
+} BackupOnCbwError;
+
+static void backup_on_cbw_error_cb_bh(void *opaque)
+{
+    BackupOnCbwError *data = opaque;
+    if (data->job) {
+        WITH_JOB_LOCK_GUARD() {
+            if (!job_is_completed_locked(data->job)) {
+                error_report("backup was cancelled because of copy-before-write error: %s",
+                             strerror(-data->ret));
+                job_cancel_locked(data->job, true);
+            }
+        }
+    } else {
+        error_report("backup_on_cbw_error_cb_bh: no job! Error: %s", strerror(-data->ret));
+    }
+
+    g_free(data);
+}
+
+static void backup_on_cbw_error_cb(void *opaque, int ret)
+{
+    BackupOnCbwError *data = g_new0(BackupOnCbwError, 1);
+    data->job = opaque;
+    data->ret = ret;
+
+    /*
+     * backup_cancel() cannot run in coroutine context.
+     */
+    if (qemu_in_coroutine()) {
+        aio_bh_schedule_oneshot(qemu_get_aio_context(), backup_on_cbw_error_cb_bh, data);
+    } else {
+        backup_on_cbw_error_cb_bh(data);
+    }
+}
+
 static void backup_cleanup_sync_bitmap(BackupBlockJob *job, int ret)
 {
     BdrvDirtyBitmap *bm;
@@ -477,6 +516,8 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
         goto error;
     }
 
+    bdrv_cbw_set_error_cb(cbw, backup_on_cbw_error_cb, job);
+
     job->cbw = cbw;
     job->source_bs = bs;
     job->target_bs = target;
-- 
2.39.2



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