Re: [PATCH V2 2/2] NFSD: allow client to use write delegation stateid for READ

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

On 2/21/25 6:42 PM, 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).
> 
> When the server offers a write delegation for an OPEN with
> OPEN4_SHARE_ACCESS_WRITE, the file access mode, the nfs4_file
> and nfs4_ol_stateid are upgraded as if the OPEN was sent with
> OPEN4_SHARE_ACCESS_BOTH.
> 
> When this delegation is returned or revoked, the corresponding open
> stateid is looked up and if it's found then the file access mode,
> the nfs4_file and nfs4_ol_stateid are downgraded to remove the read
> access.

I probably don't understand something. The patch description seems to
suggest that a WR_ONLY OPEN state ID is also granted read in this case?


> Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
> ---
>  fs/nfsd/nfs4state.c | 62 +++++++++++++++++++++++++++++++++++++++++++++
>  fs/nfsd/state.h     |  2 ++
>  2 files changed, 64 insertions(+)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index b533225e57cf..0c14f902c54c 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -6126,6 +6126,51 @@ nfs4_delegation_stat(struct nfs4_delegation *dp, struct svc_fh *currentfh,
>  	return rc == 0;
>  }
>  
> +/*
> + * Upgrade file access mode to include FMODE_READ. This is called only when
> + * a write delegation is granted for an OPEN with OPEN4_SHARE_ACCESS_WRITE.
> + */
> +static void
> +nfs4_upgrade_rdwr_file_access(struct nfs4_ol_stateid *stp)
> +{
> +	struct nfs4_file *fp = stp->st_stid.sc_file;
> +	struct nfsd_file *nflp;
> +	struct file *file;
> +
> +	spin_lock(&fp->fi_lock);
> +	nflp = fp->fi_fds[O_WRONLY];
> +	file = nflp->nf_file;
> +	file->f_mode |= FMODE_READ;
> +	swap(fp->fi_fds[O_RDWR], fp->fi_fds[O_WRONLY]);
> +	clear_access(NFS4_SHARE_ACCESS_WRITE, stp);
> +	set_access(NFS4_SHARE_ACCESS_BOTH, stp);
> +	__nfs4_file_get_access(fp, NFS4_SHARE_ACCESS_READ);	/* incr fi_access[O_RDONLY] */
> +	spin_unlock(&fp->fi_lock);
> +}
> +
> +/*
> + * Downgrade file access mode to remove FMODE_READ. This is called when
> + * a write delegation, granted for an OPEN with OPEN4_SHARE_ACCESS_WRITE,
> + * is returned.
> + */
> +static void
> +nfs4_downgrade_wronly_file_access(struct nfs4_ol_stateid *stp)
> +{
> +	struct nfs4_file *fp = stp->st_stid.sc_file;
> +	struct nfsd_file *nflp;
> +	struct file *file;
> +
> +	spin_lock(&fp->fi_lock);
> +	nflp = fp->fi_fds[O_RDWR];
> +	file = nflp->nf_file;
> +	file->f_mode &= ~FMODE_READ;
> +	swap(fp->fi_fds[O_WRONLY], fp->fi_fds[O_RDWR]);
> +	clear_access(NFS4_SHARE_ACCESS_BOTH, stp);
> +	set_access(NFS4_SHARE_ACCESS_WRITE, stp);
> +	spin_unlock(&fp->fi_lock);
> +	nfs4_file_put_access(fp, NFS4_SHARE_ACCESS_READ);	/* decr. fi_access[O_RDONLY] */
> +}
> +
>  /*
>   * The Linux NFS server does not offer write delegations to NFSv4.0
>   * clients in order to avoid conflicts between write delegations and
> @@ -6207,6 +6252,11 @@ nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
>  		dp->dl_cb_fattr.ncf_cur_fsize = stat.size;
>  		dp->dl_cb_fattr.ncf_initial_cinfo = nfsd4_change_attribute(&stat);
>  		trace_nfsd_deleg_write(&dp->dl_stid.sc_stateid);
> +
> +		if ((open->op_share_access & NFS4_SHARE_ACCESS_BOTH) == NFS4_SHARE_ACCESS_WRITE) {
> +			dp->dl_stateid = stp->st_stid.sc_stateid;
> +			nfs4_upgrade_rdwr_file_access(stp);
> +		}
>  	} else {
>  		open->op_delegate_type = deleg_ts ? OPEN_DELEGATE_READ_ATTRS_DELEG :
>  						    OPEN_DELEGATE_READ;
> @@ -7710,6 +7760,8 @@ nfsd4_delegreturn(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>  	struct nfs4_stid *s;
>  	__be32 status;
>  	struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
> +	struct nfs4_ol_stateid *stp;
> +	struct nfs4_stid *stid;
>  
>  	if ((status = fh_verify(rqstp, &cstate->current_fh, S_IFREG, 0)))
>  		return status;
> @@ -7724,6 +7776,16 @@ nfsd4_delegreturn(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>  
>  	trace_nfsd_deleg_return(stateid);
>  	destroy_delegation(dp);
> +
> +	if (dp->dl_stateid.si_generation && dp->dl_stateid.si_opaque.so_id) {
> +		if (!nfsd4_lookup_stateid(cstate, &dp->dl_stateid,
> +				SC_TYPE_OPEN, 0, &stid, nn)) {
> +			stp = openlockstateid(stid);
> +			nfs4_downgrade_wronly_file_access(stp);
> +			nfs4_put_stid(stid);
> +		}
> +	}
> +
>  	smp_mb__after_atomic();
>  	wake_up_var(d_inode(cstate->current_fh.fh_dentry));
>  put_stateid:
> diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
> index 74d2d7b42676..3f2f1b92db66 100644
> --- a/fs/nfsd/state.h
> +++ b/fs/nfsd/state.h
> @@ -207,6 +207,8 @@ struct nfs4_delegation {
>  
>  	/* for CB_GETATTR */
>  	struct nfs4_cb_fattr    dl_cb_fattr;
> +
> +	stateid_t		dl_stateid;  /* open stateid */
>  };
>  
>  static inline bool deleg_is_read(u32 dl_type)


-- 
Chuck Lever