Re: [PATCH 2/2] src/attr_replace_test: dynamically adjust the max xattr size

["Luís Henriques" <lhenriques@suse.de>]

On Wed, Jun 08, 2022 at 10:23:15AM +1000, Dave Chinner wrote:
> On Tue, Jun 07, 2022 at 04:15:13PM +0100, Luís Henriques wrote:
> > CephFS doesn't had a maximum xattr size.  Instead, it imposes a maximum
> > size for the full set of an inode's xattrs names+values, which by default
> > is 64K but it can be changed by a cluster admin.
> > 
> > Test generic/486 started to fail after fixing a ceph bug where this limit
> > wasn't being imposed.  Adjust dynamically the size of the xattr being set
> > if the error returned is -ENOSPC.
> 
> Ah, this shouldn't be getting anywhere near the 64kB limit unless
> ceph is telling userspace it's block size is > 64kB:
> 
> size = sbuf.st_blksize * 3 / 4;
> .....
> size = MIN(size, XATTR_SIZE_MAX);

Yep, that's exactly what is happening.  The cephfs kernel client reports
here the value that is being used for ceph "object size", which defaults
to 4M.  Hence, we'll set size to XATTR_SIZE_MAX.

> Regardless, the correct thing to do here is pass the max supported
> xattr size from the command line (because fstests knows what that it
> for each filesystem type) rather than hard coding
> XATTR_SIZE_MAX in the test.

OK, makes sense.  But then, for the ceph case, it becomes messy because we
also need to know the attribute name to compute the maximum size.  I guess
we'll need an extra argument for that too.

Cheers,
--
Luís