Re: [LTP] [PATCH] mremap06: fallocate is not supported on nfsv3

[Petr Vorel <pvorel@suse.cz>]

> Hi!
> > The solution would be to at least check for tst_fs_type(".") == TST_NFS_MAGIC.

> I would go for this at the moment, that is the easiest fix at the
> moment.

So you mean we risk we lost fallocate support in NFSv4.2 for the simplicity. OK
for me.

> > Perfect solution would IMHO be to check for NFS version (e.g. in /proc/mounts)
> > and TCONF only on NFSv3.

> And is nfsv4 enough, wasn't it added in nfsv4.2? Do we need to parse
> /proc/net/rpc/nfs to figure out if nfs fallocate() is supported?

Yes. First, I got confused 95d871f03cae ("nfsd: Add ALLOCATE support") [1] which is
not mentioning NFS version, because it's for nfsd. But looking other commits,
e.g. 95d871f03cae ("nfsd: Add ALLOCATE support") [2], 624bd5b7b683 ("nfs: Add
DEALLOCATE support") [3] and the docs from merge commit in 3.19 [4] and
kernelnewbies [5], it's clear: it's for NFSv4.2.

BTW is that whole fallocate() support? [4] mentions "NFSv4.2 client support for
hole punching and preallocation.", commit [3]: "This patch adds support for
using the NFS v4.2 operation DEALLOCATE to punch holes in a file.", commit
b0cb9085239a ("nfsd: Add DEALLOCATE support") [6] uses FALLOC_FL_PUNCH_HOLE
flag. All that IMHO means it's adding just FALLOC_FL_PUNCH_HOLE support into
NFSv4.2. Thus other (basic) fallocate() might work in all NFS versions, right?

That would suggest when addin safe_fallocate() we should check for NFS
(tst_fs_type(".") == TST_NFS_MAGIC) only when FALLOC_FL_PUNCH_HOLE is used.
(I got from your answer we ignore missing support for older filesystems,
we can always add the check once somebody reports invalid error).

Kind regards,
Petr

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=95d871f03cae6b49de040265cf88cbe2a16b9f05
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f4ac1674f5da420ef17896f0f222c5215ebcde80
[3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=624bd5b7b683c978c6d5f4e9f6142cfb3470983d
[4] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e20db597b6264de55ea6636fc79b1e4aaa89d129
[5] https://kernelnewbies.org/Linux_3.19#NFSv4.2_support_for_hole_punching_and_preallocation
[6] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b0cb9085239a20b7482ddd4839dd1d5476801dfa

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