Re: [PATCH v5] overlayfs: Provide a mount option "volatile" to skip sync

[Giuseppe Scrivano <gscrivan@redhat.com>]

Hi Amir,

Amir Goldstein <amir73il@gmail.com> writes:

> On Mon, Aug 24, 2020 at 11:15 AM Miklos Szeredi <miklos@szeredi.hu> wrote:
>>
>> On Sat, Aug 22, 2020 at 11:27 AM Giuseppe Scrivano <gscrivan@redhat.com> wrote:
>> >
>> > Vivek Goyal <vgoyal@redhat.com> 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? 

Thanks,
Giuseppe