On Thu, Jan 31, 2019 at 04:39:22PM +0000, Filipe Manana wrote: > On Thu, Dec 13, 2018 at 4:08 PM David Sterba <dsterba@xxxxxxx> wrote: > > > > On Wed, Dec 12, 2018 at 06:05:58PM +0000, fdmanana@xxxxxxxxxx wrote: > > > From: Filipe Manana <fdmanana@xxxxxxxx> > > > > > > Checking if the destination root is read-only was being performed only for > > > clone operations. Make deduplication check it as well, as it does not make > > > sense to not do it, even if it is an operation that does not change the > > > file contents (such as defrag for example, which checks first if the root > > > is read-only). > > > > And this is also change in user-visible behaviour of dedupe, so this > > needs to be verified if it's not breaking existing tools. > > Have you had the chance to do such verification? > > This actually conflicts with send. Send does not expect a root/tree to > change, and with dedupe on read-only roots happening > in parallel with send is going to cause all sorts of unexpected and > undesired problems... > > This is a problem introduced by dedupe ioctl when it landed, since > send existed for a longer time (when nothing else was > allowed to change read-only roots, including defrag). > > I understand it can break some applications, but adding other solution > such as preventing send and dedupe from running in parallel > (erroring out or block and wait for each other, etc) is going to be > really ugly. There's always the workaround for apps to set the > subvolume > to RW mode, do the dedupe, then switch it back to RO mode. Only if you want your incremental send chain to break on the way past... I think it's fairly clear by now (particularly from the last thread on this a couple of weeks ago) that making RO subvols RW and then back again is a fast way to broken incremental receives. Hugo. -- Hugo Mills | A clear conscience. Where did you get this taste for hugo@... carfax.org.uk | luxuries, Bernard? http://carfax.org.uk/ | Sir Humphrey PGP: E2AB1DE4 | Yes, Prime Minister
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