On Mon, Aug 24, 2020 at 4:51 PM Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > > On Mon, Aug 24, 2020 at 03:20:20PM +0200, Miklos Szeredi wrote: > > On Mon, Aug 24, 2020 at 3:02 PM Giuseppe Scrivano <gscrivan@xxxxxxxxxx> wrote: > > > > > > Amir Goldstein <amir73il@xxxxxxxxx> writes: > > > > > > > On Mon, Aug 24, 2020 at 2:39 PM Giuseppe Scrivano <gscrivan@xxxxxxxxxx> wrote: > > > >> > > > >> Hi Amir, > > > >> > > > >> Amir Goldstein <amir73il@xxxxxxxxx> writes: > > > >> > > > >> > On Mon, Aug 24, 2020 at 11:15 AM Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > > > >> >> > > > >> >> On Sat, Aug 22, 2020 at 11:27 AM Giuseppe Scrivano <gscrivan@xxxxxxxxxx> wrote: > > > >> >> > > > > >> >> > Vivek Goyal <vgoyal@xxxxxxxxxx> writes: > > > >> >> > > > > >> >> > > Container folks are complaining that dnf/yum issues too many sync while > > > >> >> > > installing packages and this slows down the image build. Build > > > >> >> > > requirement is such that they don't care if a node goes down while > > > >> >> > > build was still going on. In that case, they will simply throw away > > > >> >> > > unfinished layer and start new build. So they don't care about syncing > > > >> >> > > intermediate state to the disk and hence don't want to pay the price > > > >> >> > > associated with sync. > > > >> >> > > > > > >> >> > > > >> >> [...] > > > >> >> > > > >> >> > Ping. > > > >> >> > > > > >> >> > Is there anything holding this patch? > > > >> >> > > > >> >> Not sure what happened with protection against mounting a volatile > > > >> >> overlay twice, I don't see that in the patch. > > > >> > > > > >> > Do you mean protection only for new kernels or old kernels as well? > > > >> > > > > >> > The latter can be achieved by using $workdir/volatile/ as upperdir > > > >> > instead of $upperdir. > > > >> > Or maybe even use $workdir/work/incompat/volatile/upper, so if older > > > >> > kernel tries to re-use that $workdir, it will fail to mount rw with error: > > > >> > > > > >> > overlayfs: cleanup of 'incompat/volatile' failed (-39) > > > >> > > > > >> > If we agree to that, then upperdir= should not be provided at all when > > > >> > specifying "volatile". > > > >> > > > >> in this case, what does a program need to do to remount the overlay more > > > >> than once? Is it enough to just delete a file? > > > >> > > > > > > > > Do you mean re-mount while forgetting all changes to previous "volatile" > > > > mount? > > > > > > no, without forgetting them. > > > The original idea was to have a way to disable any sync operation in the > > > overlay file system and let the upper layers handle it. IOW, mount > > > volatile overlay+umount overlay+syncfs upper dir must still be > > > considered safe. > > > If we want to make it safer and disallow remounting the same > > > workdir+upperdir by default when "volatile" is used, that is fine; but I > > > think there should still be a way to say "I know what I am doing, just > > > remount it". > > > > Indeed. "Volatile" doesn't mean you can't use the data, just that the > > data may be lost completely in case of a crash (tmpfs analogue). > > > > Maybe just stick > > > > $(workdir)/work/incompat/volatile/donotremove > > > > in there to prevent misuse. > > So we ask users to remove "$(workdir)/work/incompat/volatile/donotremove" > if they want to remount with with same upper/ and work/? (Presumably > after syncing upper/). > Sounds right. Just don't rely on the workdir cleanup error yes? That protection is for old kernels and it falls back to r/o mount. New kernel should of course recognise $(workdir)/work/incompat/volatile fail to mount and explicitly error about unclean "volatile" unmount and maybe give a hint how to fix it in kernel log. Thanks, Amir.
