On Thu, 07/18 15:13, Paolo Bonzini wrote: > Il 18/07/2013 08:39, Fam Zheng ha scritto: > > On Wed, 07/17 13:04, Ian Main wrote: > >> This patch adds the original source drive as a backing drive to our target > >> image so that the target image will appear complete during backup. This > >> is especially useful for SYNC_MODE_NONE as it allows export via NBD to > >> have a complete point-in-time snapshot available for export. > >> > >> Signed-off-by: Ian Main <im...@redhat.com> > >> --- > >> block/backup.c | 13 +++++++++++++ > >> 1 file changed, 13 insertions(+) > >> > >> diff --git a/block/backup.c b/block/backup.c > >> index 68abd23..e086e76 100644 > >> --- a/block/backup.c > >> +++ b/block/backup.c > >> @@ -323,6 +323,10 @@ static void coroutine_fn backup_run(void *opaque) > >> > >> hbitmap_free(job->bitmap); > >> > >> + /* Set the target backing drive back to NULL before calling delete or > >> + * it will also delete the underlying drive. */ > >> + target->backing_hd = NULL; > >> + > >> bdrv_iostatus_disable(target); > >> bdrv_delete(target); > >> > >> @@ -362,6 +366,15 @@ void backup_start(BlockDriverState *bs, > >> BlockDriverState *target, > >> return; > >> } > >> > >> + /* Manually set the backing hd to be the backup source drive so > >> + * that all reads done while we are backing up will be passed > >> + * on to the original source drive. This allows reading from the > >> + * image while the backup is in progress, or in the case of > >> + * SYNC_MODE_NONE allows a complete image to be present for export. > >> + * Note that we do this for all modes including SYNC_MODE_TOP as > >> + * even then it allows on-the-fly reading. */ > >> + target->backing_hd = bs; > >> + > > > > Also set target->backing_file and target->backing_format here? Paolo? > > I don't think so, it is temporary while the job runs so that the NBD > server can already return the actual data.
OK. For NBD export, it's also going to have a name, to be used with nbd_server_add. So should we call bdrv_set_in_use() here to protect target from being used elsewhere? -- Fam