Patchwork [01/13] block: add error parameter to bdrv_snapshot_create() and related functions

diff --git a/block.c b/block.c
index 4e28c55..10e5d3e 100644
--- a/block.c
+++ b/block.c
@@ -3131,15 +3131,25 @@  BlockDriverState *bdrv_snapshots(void)
 }
 
 int bdrv_snapshot_create(BlockDriverState *bs,
-                         QEMUSnapshotInfo *sn_info)
+                         QEMUSnapshotInfo *sn_info,
+                         Error **errp)
 {
     BlockDriver *drv = bs->drv;
-    if (!drv)
+
+    if (!drv) {
+        error_setg(errp, "Device '%s' has no medium.",
+                   bdrv_get_device_name(bs));
         return -ENOMEDIUM;
-    if (drv->bdrv_snapshot_create)
-        return drv->bdrv_snapshot_create(bs, sn_info);
-    if (bs->file)
-        return bdrv_snapshot_create(bs->file, sn_info);
+    }
+    if (drv->bdrv_snapshot_create) {
+        return drv->bdrv_snapshot_create(bs, sn_info, errp);
+    }
+    if (bs->file) {
+        return bdrv_snapshot_create(bs->file, sn_info, errp);
+    }
+
+    error_setg(errp, "Snapshot is not supported for '%s'.",
+               bdrv_get_format_name(bs));
     return -ENOTSUP;
 }
 
diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index eb8fcd5..529e9ee 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -312,7 +312,9 @@  static int find_snapshot_by_id_or_name(BlockDriverState *bs, const char *name)
 }
 
 /* if no id is provided, a new one is constructed */
-int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
+int qcow2_snapshot_create(BlockDriverState *bs,
+                          QEMUSnapshotInfo *sn_info,
+                          Error **errp)
 {
     BDRVQcowState *s = bs->opaque;
     QCowSnapshot *new_snapshot_list = NULL;
@@ -331,6 +333,7 @@  int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
 
     /* Check that the ID is unique */
     if (find_snapshot_by_id(bs, sn_info->id_str) >= 0) {
+        error_setg(errp, "Parameter 'name' has to be unique ID.");
         return -EEXIST;
     }
 
@@ -348,6 +351,7 @@  int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
     l1_table_offset = qcow2_alloc_clusters(bs, s->l1_size * sizeof(uint64_t));
     if (l1_table_offset < 0) {
         ret = l1_table_offset;
+        error_setg(errp, "Failed to allocate L1 table.");
         goto fail;
     }
 
@@ -362,6 +366,7 @@  int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
     ret = bdrv_pwrite(bs->file, sn->l1_table_offset, l1_table,
                       s->l1_size * sizeof(uint64_t));
     if (ret < 0) {
+        error_setg(errp, "Failed to save L1 table.");
         goto fail;
     }
 
@@ -375,11 +380,13 @@  int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
      */
     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 1);
     if (ret < 0) {
+        error_setg(errp, "Failed to update snapshot refcount.");
         goto fail;
     }
 
     ret = bdrv_flush(bs);
     if (ret < 0) {
+        error_setg(errp, "Failed to flush data.");
         goto fail;
     }
 
@@ -397,6 +404,7 @@  int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
     if (ret < 0) {
         g_free(s->snapshots);
         s->snapshots = old_snapshot_list;
+        error_setg(errp, "Failed to write new snapshots.");
         goto fail;
     }
 
diff --git a/block/qcow2.h b/block/qcow2.h
index 718b52b..b618403 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -349,7 +349,9 @@  int qcow2_discard_clusters(BlockDriverState *bs, uint64_t offset,
 int qcow2_zero_clusters(BlockDriverState *bs, uint64_t offset, int nb_sectors);
 
 /* qcow2-snapshot.c functions */
-int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info);
+int qcow2_snapshot_create(BlockDriverState *bs,
+                          QEMUSnapshotInfo *sn_info,
+                          Error **errp);
 int qcow2_snapshot_goto(BlockDriverState *bs, const char *snapshot_id);
 int qcow2_snapshot_delete(BlockDriverState *bs, const char *snapshot_id);
 int qcow2_snapshot_list(BlockDriverState *bs, QEMUSnapshotInfo **psn_tab);
diff --git a/block/rbd.c b/block/rbd.c
index 8cd10a7..1066159 100644
--- a/block/rbd.c
+++ b/block/rbd.c
@@ -815,12 +815,14 @@  static int qemu_rbd_truncate(BlockDriverState *bs, int64_t offset)
 }
 
 static int qemu_rbd_snap_create(BlockDriverState *bs,
-                                QEMUSnapshotInfo *sn_info)
+                                QEMUSnapshotInfo *sn_info,
+                                Error **errp)
 {
     BDRVRBDState *s = bs->opaque;
     int r;
 
     if (sn_info->name[0] == '\0') {
+        error_setg(errp, "Parameter 'name' cannot be empty.");
         return -EINVAL; /* we need a name for rbd snapshots */
     }
 
@@ -830,15 +832,18 @@  static int qemu_rbd_snap_create(BlockDriverState *bs,
      */
     if (sn_info->id_str[0] != '\0' &&
         strcmp(sn_info->id_str, sn_info->name) != 0) {
+        error_setg(errp, "ID and name have to be equal.");
         return -EINVAL;
     }
 
     if (strlen(sn_info->name) >= sizeof(sn_info->id_str)) {
+        error_setg(errp, "Parameter 'name' has to be shorter that 127 chars.");
         return -ERANGE;
     }
 
     r = rbd_snap_create(s->image, sn_info->name);
     if (r < 0) {
+        error_setg(errp, "Failed to create snapshot.");
         error_report("failed to create snap: %s", strerror(-r));
         return r;
     }
diff --git a/block/sheepdog.c b/block/sheepdog.c
index e821746..aacde64 100644
--- a/block/sheepdog.c
+++ b/block/sheepdog.c
@@ -1736,7 +1736,9 @@  static int coroutine_fn sd_co_flush_to_disk(BlockDriverState *bs)
     return 0;
 }
 
-static int sd_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
+static int sd_snapshot_create(BlockDriverState *bs,
+                              QEMUSnapshotInfo *sn_info,
+                              Error **errp)
 {
     BDRVSheepdogState *s = bs->opaque;
     int ret, fd;
@@ -1749,9 +1751,8 @@  static int sd_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
             s->name, sn_info->vm_state_size, s->is_snapshot);
 
     if (s->is_snapshot) {
-        error_report("You can't create a snapshot of a snapshot VDI, "
-                     "%s (%" PRIu32 ").", s->name, s->inode.vdi_id);
-
+        error_setg(errp, "You can't create a snapshot '%s' of a VDI snapshot.",
+                   sn_info->name);
         return -EINVAL;
     }
 
@@ -1770,21 +1771,21 @@  static int sd_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
     fd = connect_to_sdog(s->addr, s->port);
     if (fd < 0) {
         ret = fd;
+        error_setg(errp, "Failed to connect to sdog.");
         goto cleanup;
     }
 
     ret = write_object(fd, (char *)&s->inode, vid_to_vdi_oid(s->inode.vdi_id),
                        s->inode.nr_copies, datalen, 0, false, s->cache_enabled);
     if (ret < 0) {
-        error_report("failed to write snapshot's inode.");
+        error_setg(errp, "Failed to write snapshot's inode.");
         goto cleanup;
     }
 
     ret = do_sd_create(s->name, s->inode.vdi_size, s->inode.vdi_id, &new_vid, 1,
                        s->addr, s->port);
     if (ret < 0) {
-        error_report("failed to create inode for snapshot. %s",
-                     strerror(errno));
+        error_setg(errp, "Failed to create inode for snapshot.");
         goto cleanup;
     }
 
@@ -1794,7 +1795,7 @@  static int sd_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
                       s->inode.nr_copies, datalen, 0, s->cache_enabled);
 
     if (ret < 0) {
-        error_report("failed to read new inode info. %s", strerror(errno));
+        error_setg(errp, "Failed to read new inode info.");
         goto cleanup;
     }
 
diff --git a/include/block/block.h b/include/block/block.h
index 0719339..bcadb72 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -321,7 +321,8 @@  int bdrv_can_snapshot(BlockDriverState *bs);
 int bdrv_is_snapshot(BlockDriverState *bs);
 BlockDriverState *bdrv_snapshots(void);
 int bdrv_snapshot_create(BlockDriverState *bs,
-                         QEMUSnapshotInfo *sn_info);
+                         QEMUSnapshotInfo *sn_info,
+                         Error **errp);
 int bdrv_snapshot_goto(BlockDriverState *bs,
                        const char *snapshot_id);
 int bdrv_snapshot_delete(BlockDriverState *bs, const char *snapshot_id);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index f83ffb8..93ef4198 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -147,7 +147,8 @@  struct BlockDriver {
                                  const uint8_t *buf, int nb_sectors);
 
     int (*bdrv_snapshot_create)(BlockDriverState *bs,
-                                QEMUSnapshotInfo *sn_info);
+                                QEMUSnapshotInfo *sn_info,
+                                Error **errp);
     int (*bdrv_snapshot_goto)(BlockDriverState *bs,
                               const char *snapshot_id);
     int (*bdrv_snapshot_delete)(BlockDriverState *bs, const char *snapshot_id);
diff --git a/qemu-img.c b/qemu-img.c
index 85d3740..5d667ae 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1564,7 +1564,7 @@  static int img_snapshot(int argc, char **argv)
         sn.date_sec = tv.tv_sec;
         sn.date_nsec = tv.tv_usec * 1000;
 
-        ret = bdrv_snapshot_create(bs, &sn);
+        ret = bdrv_snapshot_create(bs, &sn, NULL);
         if (ret) {
             error_report("Could not create snapshot '%s': %d (%s)",
                 snapshot_name, ret, strerror(-ret));
diff --git a/savevm.c b/savevm.c
index 529d60e..b1acbf1 100644
--- a/savevm.c
+++ b/savevm.c
@@ -2186,7 +2186,7 @@  void do_savevm(Monitor *mon, const QDict *qdict)
         if (bdrv_can_snapshot(bs1)) {
             /* Write VM state size only to the image that contains the state */
             sn->vm_state_size = (bs == bs1 ? vm_state_size : 0);
-            ret = bdrv_snapshot_create(bs1, sn);
+            ret = bdrv_snapshot_create(bs1, sn, NULL);
             if (ret < 0) {
                 monitor_printf(mon, "Error while creating snapshot on '%s'\n",
                                bdrv_get_device_name(bs1));