Re: [PATCH, RFCRAP] xfs: handle ENOSPC quota return in xfs_file_buffered_aio_write

[Christoph Hellwig <hch@infradead.org>]

On Mon, May 18, 2020 at 08:34:54AM -0400, Brian Foster wrote:
> Christoph's comment aside, note that the quota helpers here are filtered
> scans based on the dquots attached to the inode. It's basically an
> optimized scan when we know the failure was due to quota, so I don't
> think there should ever be a need to run a quota scan after running the
> -ENOSPC handling above. For project quota, it might make more sense to
> check if a pdquot is attached, check xfs_dquot_lowsp() and conditionally
> update the eofb to do a filtered pquota scan if appropriate (since
> calling the quota helper above would also affect other dquots attached
> to the inode, which I don't think we want to do). Then we can fall back
> to the global scan if the pquota optimization is not relevant or still
> returns -ENOSPC on the subsequent retry.

That's what I've implemented.  But it turns out -ENOSPC can of course
still mean a real -ENOSPC even with project quotas attached.  So back
to the drawing board - I think I basically need to replace the enospc
with a tristate saying what kind of scan we've tried.  Or we just ignore
the issue and keep the current global scan after a potential project
quota -ENOSPC, because all that cruft isn't worth it after all.