Re: btrfs loses 32-bit application compatibility after a while

[Florian Weimer <fweimer@redhat.com>]

* Goffredo Baroncelli:

> On 15/07/2023 11.09, Neal Gompa wrote:
>> On Sat, Jul 15, 2023 at 4:32 AM Goffredo Baroncelli <kreijack@libero.it> wrote:
>>>
> [..]
>> It was somewhat common for Fedora users. A number of Fedora 32-bit
>> ARM
>> variants used Btrfs until 32-bit ARM was discontinued in Fedora 37[1].
>> openSUSE still has 32-bit ARM and x86 support in Tumbleweed.
>> This issue is also possible on 64-bit x86 systems where 32-bit x86
>> applications run on it. That's what this report is about. We're
>> hitting it in Fedora because our 32-bit x86 builds in Fedora
>> infrastructure run on 64-bit x86 environments and triggered this[2].
>> 
>
> From what you wrote, it is seems more "it is technically supported" but not
> big users. Otherwise I expected that a lot of bugs or complaints happened
> when it was deprecated from 5.9 and removed in 5.11.

I think that for most users, it will take some time (years?) until they
hit this issue.  The builders are a bit of a special case.

This is something where telemetry really could help.

> Despite that, I am curious about what could happen when a 32 bit
> application tries to access a 64 bit inode: does the kernel return only
> the lower part of the inode number ? How this is handled in
> other FS: what happens when an fs hosts more than 2^32 files ?
> Unlikely but this may happen. BTRFS makes this more easy to happen.

The expectation is that the kernel interfaces return EOVERFLOW, the same
error code that is used for file sizes that cannot be represented using
the 32-bit interfaces.

Thanks,
Florian