block/backup: support bitmap sync modes for non-bitmap backups
Accept bitmaps and sync policies for the other backup modes.
This allows us to do things like create a bitmap synced to a full backup
without a transaction, or start a resumable backup process.
Some combinations don't make sense, though:
- NEVER policy combined with any non-BITMAP mode doesn't do anything,
because the bitmap isn't used for input or output.
It's harmless, but is almost certainly never what the user wanted.
- sync=NONE is more questionable. It can't use on-success because this
job never completes with success anyway, and the resulting artifact
of 'always' is suspect: because we start with a full bitmap and only
copy out segments that get written to, the final output bitmap will
always be ... a fully set bitmap.
Maybe there's contexts in which bitmaps make sense for sync=none,
but not without more severe changes to the current job, and omitting
it here doesn't prevent us from adding it later.
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: 20190716000117.25219-11-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>
diff --git a/blockdev.c b/blockdev.c
index f889da0..64d06d1 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3567,6 +3567,28 @@
if (bdrv_dirty_bitmap_check(bmap, BDRV_BITMAP_ALLOW_RO, errp)) {
return NULL;
}
+
+ /* This does not produce a useful bitmap artifact: */
+ if (backup->sync == MIRROR_SYNC_MODE_NONE) {
+ error_setg(errp, "sync mode '%s' does not produce meaningful bitmap"
+ " outputs", MirrorSyncMode_str(backup->sync));
+ return NULL;
+ }
+
+ /* If the bitmap isn't used for input or output, this is useless: */
+ if (backup->bitmap_mode == BITMAP_SYNC_MODE_NEVER &&
+ backup->sync != MIRROR_SYNC_MODE_BITMAP) {
+ error_setg(errp, "Bitmap sync mode '%s' has no meaningful effect"
+ " when combined with sync mode '%s'",
+ BitmapSyncMode_str(backup->bitmap_mode),
+ MirrorSyncMode_str(backup->sync));
+ return NULL;
+ }
+ }
+
+ if (!backup->has_bitmap && backup->has_bitmap_mode) {
+ error_setg(errp, "Cannot specify bitmap sync mode without a bitmap");
+ return NULL;
}
if (!backup->auto_finalize) {
