Hi Rick,

our server runs with v4.1 DSes whenissues FF layouts.
The patch is touching server side only, so I hope the
client side still works as expected. For quite some time
I had submitted a patch[0] that decomples ff layout driver
from v3 client so that client still can use v4.1 DSes
ever if v3 client in not compiled.

[0]: a68c6fbb638a "nfs41: drop dependency between flexfiles layout driver and NFSv3 modules"

Best regards,
   Tigran.


----- Original Message -----
> From: "Rick Macklem" <rick.macklem@gmail.com>
> To: "Jeff Layton" <jlayton@kernel.org>
> Cc: "Chuck Lever" <cel@kernel.org>, "NeilBrown" <neil@brown.name>, "Olga Kornievskaia" <okorniev@redhat.com>, "Dai Ngo"
> <Dai.Ngo@oracle.com>, "Tom Talpey" <tom@talpey.com>, "Tom Haynes" <thomas.haynes@hammerspace.com>, "linux-nfs"
> <linux-nfs@vger.kernel.org>, "linux-kernel" <linux-kernel@vger.kernel.org>, "Benji Wiebe" <itsme@benjiwiebe.com>
> Sent: Friday, 4 September, 2026 21:04:18
> Subject: Re: [PATCH] nfsd: don't offer flexfiles layouts when NFSv3 isn't being served

> On Fri, Sep 4, 2026 at 9:50 AM Jeff Layton <jlayton@kernel.org> wrote:
>>
>> The flexfiles layout driver hands out a deviceinfo that names this server
>> as an NFSv3 DS (flexfilelayout.c hardcodes da->version = 3). With v3
>> disabled, the client can't talk to the DS: it loops on v3 NULL calls that
>> the server answers with PROG_MISMATCH, and I/O hangs in D state.
>>
>> Skip LAYOUT_FLEX_FILES in nfsd4_setup_layout_type() unless v3 is enabled.
>>
>> Reported-by: Benji Wiebe <itsme@benjiwiebe.com>
>> Closes:
>> https://lore.kernel.org/linux-nfs/c734eeb8-8486-4491-bb4d-b9656cbaffbe@app.fastmail.com/
>> Fixes: 9b9960a0ca47 ("nfsd: Add a super simple flex file server")
>> Assisted-by: LLM
>> Signed-off-by: Jeff Layton <jlayton@kernel.org>
>> ---
>>  fs/nfsd/nfs4layouts.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/nfsd/nfs4layouts.c b/fs/nfsd/nfs4layouts.c
>> index 22bcb6d09f70..cef4d40c89a2 100644
>> --- a/fs/nfsd/nfs4layouts.c
>> +++ b/fs/nfsd/nfs4layouts.c
>> @@ -127,10 +127,12 @@ nfsd4_set_deviceid(struct nfsd4_deviceid *id, const struct
>> svc_fh *fhp,
>>
>>  void nfsd4_setup_layout_type(struct svc_export *exp)
>>  {
>> +       struct nfsd_net *nn = net_generic(exp->cd->net, nfsd_net_id);
>>         struct super_block *sb = exp->ex_path.mnt->mnt_sb;
>>         expfs_block_layouts_t block_supported = exportfs_layouts_supported(sb);
>>
>> -       if (IS_ENABLED(CONFIG_NFSD_FLEXFILELAYOUT))
>> +       if (IS_ENABLED(CONFIG_NFSD_FLEXFILELAYOUT) &&
>> +           nfsd_vers(nn, 3, NFSD_TEST))
>>                 exp->ex_layout_types |= 1 << LAYOUT_FLEX_FILES;
>>         if (IS_ENABLED(CONFIG_NFSD_BLOCKLAYOUT) &&
>>             (block_supported & EXPFS_BLOCK_IN_BAND_ID))
> Although most ffv1 servers use NFSv3 DSs, it is possible for an ffv1
> layout to specify NFSv4.
> 
> rick
> ps: I don't know how you'd check to see if the layout will be an
>      NFSv3 one. (If the server only does NFSv3 layouts, then I'd
>      guess this patch is ok?)
> 
>>
>> ---
>> base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
>> change-id: 20260904-pnfs-ff-485ac21042a6
>>
>> Best regards,
>> --
>> Jeff Layton <jlayton@kernel.org>
>>