Re: [RFC PATCH 2/4] NFSD: Never return NFS4ERR_FILE_OPEN when removing a directory

Chuck Lever
2025-01-24T14:11:40Z

On 1/24/25 5:42 AM, Amir Goldstein wrote:
> On Thu, Jan 23, 2025 at 10:07 PM Chuck Lever <chuck.lever@oracle.com> wrote:
>>
>> On 1/23/25 3:43 PM, Jeff Layton wrote:
>>> On Thu, 2025-01-23 at 14:52 -0500, cel@kernel.org wrote:
>>>> From: Chuck Lever <chuck.lever@oracle.com>
>>>>
>>>> RFC 8881 Section 18.25.4 paragraph 5 tells us that the server
>>>> should return NFS4ERR_FILE_OPEN only if the target object is an
>>>> opened file. This suggests that returning this status when removing
>>>> a directory will confuse NFS clients.
>>>>
>>>> This is a version-specific issue; nfsd_proc_remove/rmdir() and
>>>> nfsd3_proc_remove/rmdir() already return nfserr_access as
>>>> appropriate.
>>>>
>>>> Unfortunately there is no quick way for nfsd4_remove() to determine
>>>> whether the target object is a file or not, so the check is done in
>>>> to nfsd_unlink() for now.
>>>>
>>>> Reported-by: Trond Myklebust <trondmy@hammerspace.com>
>>>> Fixes: 466e16f0920f ("nfsd: check for EBUSY from vfs_rmdir/vfs_unink.")
>>>> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
>>>> ---
>>>> fs/nfsd/vfs.c | 24 ++++++++++++++++++------
>>>> 1 file changed, 18 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
>>>> index 2d8e27c225f9..3ead7fb3bf04 100644
>>>> --- a/fs/nfsd/vfs.c
>>>> +++ b/fs/nfsd/vfs.c
>>>> @@ -1931,9 +1931,17 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
>>>> return err;
>>>> }
>>>>
>>>> -/*
>>>> - * Unlink a file or directory
>>>> - * N.B. After this call fhp needs an fh_put
>>>> +/**
>>>> + * nfsd_unlink - remove a directory entry
>>>> + * @rqstp: RPC transaction context
>>>> + * @fhp: the file handle of the parent directory to be modified
>>>> + * @type: enforced file type of the object to be removed
>>>> + * @fname: the name of directory entry to be removed
>>>> + * @flen: length of @fname in octets
>>>> + *
>>>> + * After this call fhp needs an fh_put.
>>>> + *
>>>> + * Returns a generic NFS status code in network byte-order.
>>>> */
>>>> __be32
>>>> nfsd_unlink(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
>>>> @@ -2007,10 +2015,14 @@ nfsd_unlink(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
>>>> fh_drop_write(fhp);
>>>> out_nfserr:
>>>> if (host_err == -EBUSY) {
>>>> - /* name is mounted-on. There is no perfect
>>>> - * error status.
>>>> + /*
>>>> + * See RFC 8881 Section 18.25.4 para 4: NFSv4 REMOVE
>>>> + * distinguishes between reg file and dir.
>>>> */
>>>> - err = nfserr_file_open;
>>>> + if (type != S_IFDIR)
>>>
>>> Should that be "if (type == S_ISREG)" instead? What if the inode is a
>>> named pipe or device file? I'm not sure you can ever get EBUSY with
>>> those, but in case you can, what's the right error in those cases?

Another way to put this:

If a client can acquire an OPEN state ID for those types of objects,
then NFS4ERR_FILE_OPEN is the correct status code in those cases.

But in practice, it depends on what existing client implementations
expect.

>> Check out nfsd_unlink()'s callers to see what they pass as the type
>> parameter. Unfortunately we have to compare against S_IFDIR here.
>>
>
> Not exactly. nfsd4_remove() is the only caller that needs to get
> nfserr_file_open and this caller calls with type = 0, so type here
> is going to be the actual type of the inode and (type == S_ISREG)
> would be correct. No?

--
Chuck Lever