Re: [PATCH v3 2/2] NFSD: enable support for write delegation

[dai.ngo@xxxxxxxxxx]

On 5/18/23 6:23 AM, Chuck Lever III wrote:
> > On May 17, 2023, at 7:38 PM, Dai Ngo <dai.ngo@xxxxxxxxxx> wrote:
> >
> > This patch grants write delegation for OPEN with NFS4_SHARE_ACCESS_WRITE
> > if there is no conflict with other OPENs.
> >
> > Write delegation conflict with another OPEN, REMOVE, RENAME and SETATTR
> > are handled the same as read delegation using notify_change,
> > try_break_deleg.
> Very clean. A couple of suggestions, one is down below, and here is
> the other:
>
> I was thinking we should add one or two counters in fs/nfsd/stats.c
> to track how often read and write delegations are offered, and
> perhaps one to count the number of DELEGRETURN operations. What do
> you think makes sense?

I'm not sure what these counters will tell us, currently we already
has a counter for number of delegations handed out. I think a counter
on how often nfsd has to recall the write delegation due to GETATTR can
be useful to know whether we should implement CB_GETATTR.

> > Signed-off-by: Dai Ngo <dai.ngo@xxxxxxxxxx>
> > ---
> > fs/nfsd/nfs4state.c | 24 ++++++++++++++++--------
> > 1 file changed, 16 insertions(+), 8 deletions(-)
> >
> > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> > index 6e61fa3acaf1..09a9e16407f9 100644
> > --- a/fs/nfsd/nfs4state.c
> > +++ b/fs/nfsd/nfs4state.c
> > @@ -1144,7 +1144,7 @@ static void block_delegations(struct knfsd_fh *fh)
> >
> > static struct nfs4_delegation *
> > alloc_init_deleg(struct nfs4_client *clp, struct nfs4_file *fp,
> > - struct nfs4_clnt_odstate *odstate)
> > + struct nfs4_clnt_odstate *odstate, u32 dl_type)
> > {
> > struct nfs4_delegation *dp;
> > long n;
> > @@ -1170,7 +1170,7 @@ alloc_init_deleg(struct nfs4_client *clp, struct nfs4_file *fp,
> > INIT_LIST_HEAD(&dp->dl_recall_lru);
> > dp->dl_clnt_odstate = odstate;
> > get_clnt_odstate(odstate);
> > - dp->dl_type = NFS4_OPEN_DELEGATE_READ;
> > + dp->dl_type = dl_type;
> > dp->dl_retries = 1;
> > dp->dl_recalled = false;
> > nfsd4_init_cb(&dp->dl_recall, dp->dl_stid.sc_client,
> > @@ -5451,6 +5451,7 @@ nfs4_set_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> > struct nfs4_delegation *dp;
> > struct nfsd_file *nf;
> > struct file_lock *fl;
> > + u32 deleg;
> >
> > /*
> > * The fi_had_conflict and nfs_get_existing_delegation checks
> > @@ -5460,7 +5461,13 @@ nfs4_set_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> > if (fp->fi_had_conflict)
> > return ERR_PTR(-EAGAIN);
> >
> > - nf = find_readable_file(fp);
> > + if (open->op_share_access & NFS4_SHARE_ACCESS_WRITE) {
> > + nf = find_writeable_file(fp);
> > + deleg = NFS4_OPEN_DELEGATE_WRITE;
> > + } else {
> > + nf = find_readable_file(fp);
> > + deleg = NFS4_OPEN_DELEGATE_READ;
> > + }
> > if (!nf) {
> > /*
> > * We probably could attempt another open and get a read
> > @@ -5491,11 +5498,11 @@ nfs4_set_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> > return ERR_PTR(status);
> >
> > status = -ENOMEM;
> > - dp = alloc_init_deleg(clp, fp, odstate);
> > + dp = alloc_init_deleg(clp, fp, odstate, deleg);
> > if (!dp)
> > goto out_delegees;
> >
> > - fl = nfs4_alloc_init_lease(dp, NFS4_OPEN_DELEGATE_READ);
> > + fl = nfs4_alloc_init_lease(dp, deleg);
> > if (!fl)
> > goto out_clnt_odstate;
> >
> > @@ -5583,6 +5590,7 @@ nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> > struct svc_fh *parent = NULL;
> > int cb_up;
> > int status = 0;
> > + u32 wdeleg = false;
> >
> > cb_up = nfsd4_cb_channel_good(oo->oo_owner.so_client);
> > open->op_recall = 0;
> > @@ -5590,8 +5598,6 @@ nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> > case NFS4_OPEN_CLAIM_PREVIOUS:
> > if (!cb_up)
> > open->op_recall = 1;
> > - if (open->op_delegate_type != NFS4_OPEN_DELEGATE_READ)
> > - goto out_no_deleg;
> > break;
> > case NFS4_OPEN_CLAIM_NULL:
> > parent = currentfh;
> > @@ -5617,7 +5623,9 @@ 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));
> >
> > trace_nfsd_deleg_read(&dp->dl_stid.sc_stateid);
> I'd like you to add a trace_nfsd_deleg_write(), and invoke
> it here instead of trace_nfsd_deleg_read when NFSD hands out
> a write delegation.

Fix in v4.

-Dai

> > - open->op_delegate_type = NFS4_OPEN_DELEGATE_READ;
> > + wdeleg = open->op_share_access & NFS4_SHARE_ACCESS_WRITE;
> > + open->op_delegate_type = wdeleg ?
> > + NFS4_OPEN_DELEGATE_WRITE : NFS4_OPEN_DELEGATE_READ;
> > nfs4_put_stid(&dp->dl_stid);
> > return;
> > out_no_deleg:
> > --
> > 2.9.5
> --
> Chuck Lever