On Fri, Apr 15, 2016 at 11:27:55AM +0800, Fam Zheng wrote:
> virtlockd in libvirt locks the first byte, we lock byte 1 to avoid
> the intervene.
> +static int raw_lockf(BlockDriverState *bs, BdrvLockfCmd cmd)
> +{
> +
> + BDRVRawState *s = bs->opaque;
> + int ret;
> + struct flock fl = (struct flock) {
> + .l_whence = SEEK_SET,
> + /* Locking byte 1 avoids interfereing with virtlockd. */
> + .l_start = 1,
> + .l_len = 1,
> + };
> +
> + switch (cmd) {
> + case BDRV_LOCKF_RWLOCK:
> + fl.l_type = F_WRLCK;
> + break;
> + case BDRV_LOCKF_ROLOCK:
> + fl.l_type = F_RDLCK;
> + break;
> + case BDRV_LOCKF_UNLOCK:
> + fl.l_type = F_UNLCK;
> + break;
My understanding is this prevents libguestfs from working on live disk
images -- we want to be able to read live disk images (using a
writable overlay and the real disk image as a read-only backing file).
So please don't do this; or suggest how we can ignore the lock for
backing files.
Rich.
--
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