[ Cc: Fam ] Am 10.10.2017 um 15:42 hat Vladimir Sementsov-Ogievskiy geschrieben: > We do not reopen lock_fd on bdrv_reopen which leads to problems on > reopen image RO. So, lets make lock_fd be always RO. > This is correct, because qemu_lock_fd always called with exclusive=false > on lock_fd. > > Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> > --- > > Hi all! > > We've faced the following problem with our shared-storage migration > scheme. We make an external snapshot and need base image to be reopened > RO. However, bdrv_reopen reopens only .fd of BDRVRawState but not > .lock_fd. So, .lock_fd is left opened RW and this breaks the whole > thing. > > The simple fix is here: let's just open lock_fd as RO always. This > looks fine for current code, as we never try to set write locks > (qemu_lock_fd always called with exclusive=false). > > However it will not work if we are going to use write locks.
I was sure that we had discussed this during review, so I just went back and checked. Indeed, Fam originally had an unconditional O_RDONLY in some version of the image locking patches, but I actually found a potential problem with that back then: > Note that with /dev/fdset there can be cases where we can open a file > O_RDWR, but not O_RDONLY. Should we better just use the same flags as > for the s->fd? https://lists.gnu.org/archive/html/qemu-devel/2017-04/msg05107.html However, I'm now wondering whether we really still need a separate s->lock_fd or whether we can just use the normal image fd for this. If I understood the old threads correctly, the original reason for it was that during bdrv_reopen(), we couldn't safely migrate exclusive locks from the old fd to the new one. But as we aren't using exclusive locks any more, this shouldn't be a problem today. Fam, are there more reasons why we need a separate lock_fd? Kevin
