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block/backup: support bitmap sync modes for non-bitmap backups

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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>
This commit is contained in:
John Snow
2019-07-29 16:35:55 -04:00
parent 7e30dd618e
commit 1a2b8b406b
3 changed files with 27 additions and 9 deletions
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22
blockdev.c
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@ -3567,6 +3567,28 @@ static BlockJob *do_backup_common(BackupCommon *backup,
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) {