Re: [PATCH V4 1/2] NFSD: Offer write delegation for OPEN with OPEN4_SHARE_ACCESS_WRITE

[Chuck Lever <chuck.lever@oracle.com>]

On 3/5/25 9:36 AM, Jeff Layton wrote:
> On Tue, 2025-03-04 at 12:38 -0800, Dai Ngo wrote:
>> RFC8881, section 9.1.2 says:
>>
>>   "In the case of READ, the server may perform the corresponding
>>    check on the access mode, or it may choose to allow READ for
>>    OPEN4_SHARE_ACCESS_WRITE, to accommodate clients whose WRITE
>>    implementation may unavoidably do (e.g., due to buffer cache
>>    constraints)."
>>
>> and in section 10.4.1:
>>    "Similarly, when closing a file opened for OPEN4_SHARE_ACCESS_WRITE/
>>    OPEN4_SHARE_ACCESS_BOTH and if an OPEN_DELEGATE_WRITE delegation
>>    is in effect"
>>
>> This patch offers write delegation for OPEN with OPEN4_SHARE_ACCESS_WRITE
>> only. Also deleted no longer use find_rw_file().
>>
>> Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
>> ---
>>  fs/nfsd/nfs4state.c | 34 +++++++++++++---------------------
>>  1 file changed, 13 insertions(+), 21 deletions(-)
>>
>> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
>> index 0f97f2c62b3a..b533225e57cf 100644
>> --- a/fs/nfsd/nfs4state.c
>> +++ b/fs/nfsd/nfs4state.c
>> @@ -633,18 +633,6 @@ find_readable_file(struct nfs4_file *f)
>>  	return ret;
>>  }
>>  
>> -static struct nfsd_file *
>> -find_rw_file(struct nfs4_file *f)
>> -{
>> -	struct nfsd_file *ret;
>> -
>> -	spin_lock(&f->fi_lock);
>> -	ret = nfsd_file_get(f->fi_fds[O_RDWR]);
>> -	spin_unlock(&f->fi_lock);
>> -
>> -	return ret;
>> -}
>> -
>>  struct nfsd_file *
>>  find_any_file(struct nfs4_file *f)
>>  {
>> @@ -5382,7 +5370,6 @@ static int nfsd4_cb_recall_done(struct nfsd4_callback *cb,
>>  	if (dp->dl_stid.sc_status)
>>  		/* CLOSED or REVOKED */
>>  		return 1;
>> -
>>  	switch (task->tk_status) {
>>  	case 0:
>>  		return 1;
>> @@ -5987,14 +5974,19 @@ nfs4_set_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
>>  	 *  "An OPEN_DELEGATE_WRITE delegation allows the client to handle,
>>  	 *   on its own, all opens."
>>  	 *
>> -	 * Furthermore the client can use a write delegation for most READ
>> -	 * operations as well, so we require a O_RDWR file here.
>> +	 * Furthermore, section 9.1.2 says:
>> +	 *
>> +	 *  "In the case of READ, the server may perform the corresponding
>> +	 *  check on the access mode, or it may choose to allow READ for
>> +	 *  OPEN4_SHARE_ACCESS_WRITE, to accommodate clients whose WRITE
>> +	 *  implementation may unavoidably do (e.g., due to buffer cache
>> +	 *  constraints)."
>>  	 *
>> -	 * Offer a write delegation in the case of a BOTH open, and ensure
>> -	 * we get the O_RDWR descriptor.
>> +	 *  We choose to offer a write delegation for OPEN with the
>> +	 *  OPEN4_SHARE_ACCESS_WRITE access mode to accommodate such clients.
>>  	 */
>> -	if ((open->op_share_access & NFS4_SHARE_ACCESS_BOTH) == NFS4_SHARE_ACCESS_BOTH) {
>> -		nf = find_rw_file(fp);
>> +	if (open->op_share_access & NFS4_SHARE_ACCESS_WRITE) {
>> +		nf = find_writeable_file(fp);
>>  		dl_type = deleg_ts ? OPEN_DELEGATE_WRITE_ATTRS_DELEG : OPEN_DELEGATE_WRITE;
>>  	}
>>  
>> @@ -6116,7 +6108,7 @@ static bool
>>  nfs4_delegation_stat(struct nfs4_delegation *dp, struct svc_fh *currentfh,
>>  		     struct kstat *stat)
>>  {
>> -	struct nfsd_file *nf = find_rw_file(dp->dl_stid.sc_file);
>> +	struct nfsd_file *nf = find_writeable_file(dp->dl_stid.sc_file);
>>  	struct path path;
>>  	int rc;
>>  
>> @@ -7063,7 +7055,7 @@ nfsd4_lookup_stateid(struct nfsd4_compound_state *cstate,
>>  		return_revoked = true;
>>  	if (typemask & SC_TYPE_DELEG)
>>  		/* Always allow REVOKED for DELEG so we can
>> -		 * retturn the appropriate error.
>> +		 * return the appropriate error.
>>  		 */
>>  		statusmask |= SC_STATUS_REVOKED;
>>  
> 
> This patch also looks good.
> 
> The only other issue I have with this is the patch ordering. If a
> bisect lands between these two patches then delegations won't work
> quite right. Is there a reason to order the patches this way?

I also wondered about the patch order for the same reason.


> Reviewed-by: Jeff Layton <jlayton@kernel.org>


-- 
Chuck Lever