Re: [PATCH V4 2/2] NFSD: allow client to use write delegation stateid for READ

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

On 3/5/25 9:34 AM, Jeff Layton wrote:
> On Tue, 2025-03-04 at 12:38 -0800, Dai Ngo wrote:
>> Allow READ using write delegation stateid granted on OPENs with
>> OPEN4_SHARE_ACCESS_WRITE only, to accommodate clients whose WRITE
>> implementation may unavoidably do (e.g., due to buffer cache
>> constraints).
>>
>> For write delegation granted for OPEN with OPEN4_SHARE_ACCESS_WRITE
>> a new nfsd_file and a struct file are allocated to use for reads.
>> The nfsd_file is freed when the file is closed by release_all_access.
>>
>> Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
>> ---
>>  fs/nfsd/nfs4state.c | 44 ++++++++++++++++++++++++++++++++++++--------
>>  1 file changed, 36 insertions(+), 8 deletions(-)
>>
>> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
>> index b533225e57cf..35018af4e7fb 100644
>> --- a/fs/nfsd/nfs4state.c
>> +++ b/fs/nfsd/nfs4state.c
>> @@ -6126,6 +6126,34 @@ nfs4_delegation_stat(struct nfs4_delegation *dp, struct svc_fh *currentfh,
>>  	return rc == 0;
>>  }
>>  
>> +/*
>> + * Add NFS4_SHARE_ACCESS_READ to the write delegation granted on OPEN
>> + * with NFS4_SHARE_ACCESS_WRITE by allocating separate nfsd_file and
>> + * struct file to be used for read with delegation stateid.
>> + *
>> + */
>> +static bool
>> +nfsd4_add_rdaccess_to_wrdeleg(struct svc_rqst *rqstp, struct nfsd4_open *open,
>> +			      struct svc_fh *fh, struct nfs4_ol_stateid *stp)
>> +{
>> +	struct nfs4_file *fp;
>> +	struct nfsd_file *nf = NULL;
>> +
>> +	if ((open->op_share_access & NFS4_SHARE_ACCESS_BOTH) ==
>> +			NFS4_SHARE_ACCESS_WRITE) {
>> +		if (nfsd_file_acquire_opened(rqstp, fh, NFSD_MAY_READ, NULL, &nf))
>> +			return (false);
>> +		fp = stp->st_stid.sc_file;
>> +		spin_lock(&fp->fi_lock);
>> +		__nfs4_file_get_access(fp, NFS4_SHARE_ACCESS_READ);
>> +		set_access(NFS4_SHARE_ACCESS_READ, stp);
>> +		fp = stp->st_stid.sc_file;
>> +		fp->fi_fds[O_RDONLY] = nf;
>> +		spin_unlock(&fp->fi_lock);
>> +	}
>> +	return (true);
> 
> no need for parenthesis here ^^^
> 
>> +}
>> +
>>  /*
>>   * The Linux NFS server does not offer write delegations to NFSv4.0
>>   * clients in order to avoid conflicts between write delegations and
>> @@ -6151,8 +6179,9 @@ nfs4_delegation_stat(struct nfs4_delegation *dp, struct svc_fh *currentfh,
>>   * open or lock state.
>>   */
>>  static void
>> -nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
>> -		     struct svc_fh *currentfh)
>> +nfs4_open_delegation(struct svc_rqst *rqstp, struct nfsd4_open *open,
>> +		     struct nfs4_ol_stateid *stp, struct svc_fh *currentfh,
>> +		     struct svc_fh *fh)
>>  {
>>  	bool deleg_ts = open->op_deleg_want & OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS;
>>  	struct nfs4_openowner *oo = openowner(stp->st_stateowner);
>> @@ -6197,7 +6226,8 @@ nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
>>  	memcpy(&open->op_delegate_stateid, &dp->dl_stid.sc_stateid, sizeof(dp->dl_stid.sc_stateid));
>>  
>>  	if (open->op_share_access & NFS4_SHARE_ACCESS_WRITE) {
>> -		if (!nfs4_delegation_stat(dp, currentfh, &stat)) {
>> +		if ((!nfsd4_add_rdaccess_to_wrdeleg(rqstp, open, fh, stp)) ||
> 
> extra set of parens above too ^^^
> 
>> +				!nfs4_delegation_stat(dp, currentfh, &stat)) {
>>  			nfs4_put_stid(&dp->dl_stid);
>>  			destroy_delegation(dp);
>>  			goto out_no_deleg;
>> @@ -6353,7 +6383,8 @@ nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
>>  	* Attempt to hand out a delegation. No error return, because the
>>  	* OPEN succeeds even if we fail.
>>  	*/
>> -	nfs4_open_delegation(open, stp, &resp->cstate.current_fh);
>> +	nfs4_open_delegation(rqstp, open, stp,
>> +		&resp->cstate.current_fh, current_fh);
>>  
>>  	/*
>>  	 * If there is an existing open stateid, it must be updated and
>> @@ -7098,10 +7129,6 @@ nfs4_find_file(struct nfs4_stid *s, int flags)
>>  
>>  	switch (s->sc_type) {
>>  	case SC_TYPE_DELEG:
>> -		spin_lock(&s->sc_file->fi_lock);
>> -		ret = nfsd_file_get(s->sc_file->fi_deleg_file);
>> -		spin_unlock(&s->sc_file->fi_lock);
>> -		break;
>>  	case SC_TYPE_OPEN:
>>  	case SC_TYPE_LOCK:
>>  		if (flags & RD_STATE)
>> @@ -7277,6 +7304,7 @@ nfs4_preprocess_stateid_op(struct svc_rqst *rqstp,
>>  		status = find_cpntf_state(nn, stateid, &s);
>>  	if (status)
>>  		return status;
>> +
>>  	status = nfsd4_stid_check_stateid_generation(stateid, s,
>>  			nfsd4_has_session(cstate));
>>  	if (status)
> 
> Patch itself looks good though, so with the nits fixed up, you can add:
> 
> Reviewed-by: Jeff Layton <jlayton@kernel.org>

Dai, I can fix the parentheses in my tree, no need for a v5.


-- 
Chuck Lever