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Date:   Mon, 15 May 2023 11:26:40 -0700
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Subject: Re: [PATCH v2 4/4] NFSD: handle GETATTR conflict with write
 delegation
Content-Language: en-US
To:     Olga Kornievskaia <aglo@umich.edu>
Cc:     chuck.lever@oracle.com, jlayton@kernel.org,
        linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org
References: <1684110038-11266-1-git-send-email-dai.ngo@oracle.com>
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From:   dai.ngo@oracle.com
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On 5/15/23 11:14 AM, Olga Kornievskaia wrote:
> On Sun, May 14, 2023 at 8:56 PM Dai Ngo <dai.ngo@oracle.com> wrote:
>> If the GETATTR request on a file that has write delegation in effect
>> and the request attributes include the change info and size attribute
>> then the request is handled as below:
>>
>> Server sends CB_GETATTR to client to get the latest change info and file
>> size. If these values are the same as the server's cached values then
>> the GETATTR proceeds as normal.
>>
>> If either the change info or file size is different from the server's
>> cached values, or the file was already marked as modified, then:
>>
>>     . update time_modify and time_metadata into file's metadata
>>       with current time
>>
>>     . encode GETATTR as normal except the file size is encoded with
>>       the value returned from CB_GETATTR
>>
>>     . mark the file as modified
>>
>> If the CB_GETATTR fails for any reasons, the delegation is recalled
>> and NFS4ERR_DELAY is returned for the GETATTR.
> Hi Dai,
>
> I'm curious what does the server gain by implementing handling of
> GETATTR with delegations? As far as I can tell it is not strictly
> required by the RFC(s). When the file is being written any attempt at
> querying its attribute is immediately stale.

Yes, you're right that handling of GETATTR with delegations is not
required by the spec. The only benefit I see is that the server
provides a more accurate state of the file as whether the file has
been changed/updated since the client's last GETATTR. This allows
the app on the client to take appropriate action (whatever that
might be) when sharing files among multiple clients.

-Dai

>
>> Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
>> ---
>>   fs/nfsd/nfs4state.c | 58 ++++++++++++++++++++++++++++++++++++
>>   fs/nfsd/nfs4xdr.c   | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
>>   fs/nfsd/state.h     |  7 +++++
>>   3 files changed, 148 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
>> index 09a9e16407f9..fb305b28a090 100644
>> --- a/fs/nfsd/nfs4state.c
>> +++ b/fs/nfsd/nfs4state.c
>> @@ -127,6 +127,7 @@ static void free_session(struct nfsd4_session *);
>>
>>   static const struct nfsd4_callback_ops nfsd4_cb_recall_ops;
>>   static const struct nfsd4_callback_ops nfsd4_cb_notify_lock_ops;
>> +static const struct nfsd4_callback_ops nfsd4_cb_getattr_ops;
>>
>>   static struct workqueue_struct *laundry_wq;
>>
>> @@ -1175,6 +1176,10 @@ alloc_init_deleg(struct nfs4_client *clp, struct nfs4_file *fp,
>>          dp->dl_recalled = false;
>>          nfsd4_init_cb(&dp->dl_recall, dp->dl_stid.sc_client,
>>                        &nfsd4_cb_recall_ops, NFSPROC4_CLNT_CB_RECALL);
>> +       nfsd4_init_cb(&dp->dl_cb_fattr.ncf_getattr, dp->dl_stid.sc_client,
>> +                       &nfsd4_cb_getattr_ops, NFSPROC4_CLNT_CB_GETATTR);
>> +       dp->dl_cb_fattr.ncf_file_modified = false;
>> +       dp->dl_cb_fattr.ncf_cb_bmap[0] = FATTR4_WORD0_CHANGE | FATTR4_WORD0_SIZE;
>>          get_nfs4_file(fp);
>>          dp->dl_stid.sc_file = fp;
>>          return dp;
>> @@ -2882,11 +2887,49 @@ nfsd4_cb_recall_any_release(struct nfsd4_callback *cb)
>>          spin_unlock(&nn->client_lock);
>>   }
>>
>> +static int
>> +nfsd4_cb_getattr_done(struct nfsd4_callback *cb, struct rpc_task *task)
>> +{
>> +       struct nfs4_cb_fattr *ncf =
>> +               container_of(cb, struct nfs4_cb_fattr, ncf_getattr);
>> +
>> +       ncf->ncf_cb_status = task->tk_status;
>> +       switch (task->tk_status) {
>> +       case -NFS4ERR_DELAY:
>> +               rpc_delay(task, 2 * HZ);
>> +               return 0;
>> +       default:
>> +               return 1;
>> +       }
>> +}
>> +
>> +static void
>> +nfsd4_cb_getattr_release(struct nfsd4_callback *cb)
>> +{
>> +       struct nfs4_cb_fattr *ncf =
>> +               container_of(cb, struct nfs4_cb_fattr, ncf_getattr);
>> +
>> +       clear_bit(CB_GETATTR_BUSY, &ncf->ncf_cb_flags);
>> +       wake_up_bit(&ncf->ncf_cb_flags, CB_GETATTR_BUSY);
>> +}
>> +
>>   static const struct nfsd4_callback_ops nfsd4_cb_recall_any_ops = {
>>          .done           = nfsd4_cb_recall_any_done,
>>          .release        = nfsd4_cb_recall_any_release,
>>   };
>>
>> +static const struct nfsd4_callback_ops nfsd4_cb_getattr_ops = {
>> +       .done           = nfsd4_cb_getattr_done,
>> +       .release        = nfsd4_cb_getattr_release,
>> +};
>> +
>> +void nfs4_cb_getattr(struct nfs4_cb_fattr *ncf)
>> +{
>> +       if (test_and_set_bit(CB_GETATTR_BUSY, &ncf->ncf_cb_flags))
>> +               return;
>> +       nfsd4_run_cb(&ncf->ncf_getattr);
>> +}
>> +
>>   static struct nfs4_client *create_client(struct xdr_netobj name,
>>                  struct svc_rqst *rqstp, nfs4_verifier *verf)
>>   {
>> @@ -5591,6 +5634,8 @@ nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
>>          int cb_up;
>>          int status = 0;
>>          u32 wdeleg = false;
>> +       struct kstat stat;
>> +       struct path path;
>>
>>          cb_up = nfsd4_cb_channel_good(oo->oo_owner.so_client);
>>          open->op_recall = 0;
>> @@ -5626,6 +5671,19 @@ nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
>>          wdeleg = open->op_share_access & NFS4_SHARE_ACCESS_WRITE;
>>          open->op_delegate_type = wdeleg ?
>>                          NFS4_OPEN_DELEGATE_WRITE : NFS4_OPEN_DELEGATE_READ;
>> +       if (wdeleg) {
>> +               path.mnt = currentfh->fh_export->ex_path.mnt;
>> +               path.dentry = currentfh->fh_dentry;
>> +               if (vfs_getattr(&path, &stat, STATX_BASIC_STATS,
>> +                                               AT_STATX_SYNC_AS_STAT)) {
>> +                       nfs4_put_stid(&dp->dl_stid);
>> +                       destroy_delegation(dp);
>> +                       goto out_no_deleg;
>> +               }
>> +               dp->dl_cb_fattr.ncf_cur_fsize = stat.size;
>> +               dp->dl_cb_fattr.ncf_initial_cinfo = nfsd4_change_attribute(&stat,
>> +                                                       d_inode(currentfh->fh_dentry));
>> +       }
>>          nfs4_put_stid(&dp->dl_stid);
>>          return;
>>   out_no_deleg:
>> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
>> index 76db2fe29624..5d7e11db8ccf 100644
>> --- a/fs/nfsd/nfs4xdr.c
>> +++ b/fs/nfsd/nfs4xdr.c
>> @@ -2920,6 +2920,77 @@ nfsd4_encode_bitmap(struct xdr_stream *xdr, u32 bmval0, u32 bmval1, u32 bmval2)
>>          return nfserr_resource;
>>   }
>>
>> +static struct file_lock *
>> +nfs4_wrdeleg_filelock(struct svc_rqst *rqstp, struct inode *inode)
>> +{
>> +       struct file_lock_context *ctx;
>> +       struct file_lock *fl;
>> +
>> +       ctx = locks_inode_context(inode);
>> +       if (!ctx)
>> +               return NULL;
>> +       spin_lock(&ctx->flc_lock);
>> +       list_for_each_entry(fl, &ctx->flc_lease, fl_list) {
>> +               if (fl->fl_type == F_WRLCK) {
>> +                       spin_unlock(&ctx->flc_lock);
>> +                       return fl;
>> +               }
>> +       }
>> +       spin_unlock(&ctx->flc_lock);
>> +       return NULL;
>> +}
>> +
>> +static __be32
>> +nfs4_handle_wrdeleg_conflict(struct svc_rqst *rqstp, struct inode *inode,
>> +                       bool *modified, u64 *size)
>> +{
>> +       __be32 status;
>> +       struct file_lock *fl;
>> +       struct nfs4_delegation *dp;
>> +       struct nfs4_cb_fattr *ncf;
>> +       struct iattr attrs;
>> +
>> +       *modified = false;
>> +       fl = nfs4_wrdeleg_filelock(rqstp, inode);
>> +       if (!fl)
>> +               return 0;
>> +       dp = fl->fl_owner;
>> +       ncf = &dp->dl_cb_fattr;
>> +       if (dp->dl_recall.cb_clp == *(rqstp->rq_lease_breaker))
>> +               return 0;
>> +
>> +       refcount_inc(&dp->dl_stid.sc_count);
>> +       nfs4_cb_getattr(&dp->dl_cb_fattr);
>> +       wait_on_bit(&ncf->ncf_cb_flags, CB_GETATTR_BUSY, TASK_INTERRUPTIBLE);
>> +       if (ncf->ncf_cb_status) {
>> +               status = nfserrno(nfsd_open_break_lease(inode, NFSD_MAY_READ));
>> +               nfs4_put_stid(&dp->dl_stid);
>> +               return status;
>> +       }
>> +       ncf->ncf_cur_fsize = ncf->ncf_cb_fsize;
>> +       if (!ncf->ncf_file_modified &&
>> +                       (ncf->ncf_initial_cinfo != ncf->ncf_cb_change ||
>> +                       ncf->ncf_cur_fsize != ncf->ncf_cb_fsize)) {
>> +               ncf->ncf_file_modified = true;
>> +       }
>> +
>> +       if (ncf->ncf_file_modified) {
>> +               /*
>> +                * The server would not update the file's metadata
>> +                * with the client's modified size.
>> +                * nfsd4 change attribute is constructed from ctime.
>> +                */
>> +               attrs.ia_mtime = attrs.ia_ctime = current_time(inode);
>> +               attrs.ia_valid = ATTR_MTIME | ATTR_CTIME;
>> +               setattr_copy(&nop_mnt_idmap, inode, &attrs);
>> +               mark_inode_dirty(inode);
>> +               *size = ncf->ncf_cur_fsize;
>> +               *modified = true;
>> +       }
>> +       nfs4_put_stid(&dp->dl_stid);
>> +       return 0;
>> +}
>> +
>>   /*
>>    * Note: @fhp can be NULL; in this case, we might have to compose the filehandle
>>    * ourselves.
>> @@ -2957,6 +3028,8 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
>>                  .dentry = dentry,
>>          };
>>          struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
>> +       bool file_modified;
>> +       u64 size = 0;
>>
>>          BUG_ON(bmval1 & NFSD_WRITEONLY_ATTRS_WORD1);
>>          BUG_ON(!nfsd_attrs_supported(minorversion, bmval));
>> @@ -2966,6 +3039,12 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
>>                  if (status)
>>                          goto out;
>>          }
>> +       if (bmval0 & (FATTR4_WORD0_CHANGE | FATTR4_WORD0_SIZE)) {
>> +               status = nfs4_handle_wrdeleg_conflict(rqstp, d_inode(dentry),
>> +                                               &file_modified, &size);
>> +               if (status)
>> +                       goto out;
>> +       }
>>
>>          err = vfs_getattr(&path, &stat,
>>                            STATX_BASIC_STATS | STATX_BTIME | STATX_CHANGE_COOKIE,
>> @@ -3089,7 +3168,10 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
>>                  p = xdr_reserve_space(xdr, 8);
>>                  if (!p)
>>                          goto out_resource;
>> -               p = xdr_encode_hyper(p, stat.size);
>> +               if (file_modified)
>> +                       p = xdr_encode_hyper(p, size);
>> +               else
>> +                       p = xdr_encode_hyper(p, stat.size);
>>          }
>>          if (bmval0 & FATTR4_WORD0_LINK_SUPPORT) {
>>                  p = xdr_reserve_space(xdr, 4);
>> diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
>> index 9fb69ed8ae80..b20b65fe89b4 100644
>> --- a/fs/nfsd/state.h
>> +++ b/fs/nfsd/state.h
>> @@ -121,6 +121,10 @@ struct nfs4_cb_fattr {
>>          struct nfsd4_callback ncf_getattr;
>>          u32 ncf_cb_status;
>>          u32 ncf_cb_bmap[1];
>> +       unsigned long ncf_cb_flags;
>> +       bool ncf_file_modified;
>> +       u64 ncf_initial_cinfo;
>> +       u64 ncf_cur_fsize;
>>
>>          /* from CB_GETATTR reply */
>>          u64 ncf_cb_change;
>> @@ -744,6 +748,9 @@ extern void nfsd4_client_record_remove(struct nfs4_client *clp);
>>   extern int nfsd4_client_record_check(struct nfs4_client *clp);
>>   extern void nfsd4_record_grace_done(struct nfsd_net *nn);
>>
>> +/* CB_GETTTAR */
>> +extern void nfs4_cb_getattr(struct nfs4_cb_fattr *ncf);
>> +
>>   static inline bool try_to_expire_client(struct nfs4_client *clp)
>>   {
>>          cmpxchg(&clp->cl_state, NFSD4_COURTESY, NFSD4_EXPIRABLE);
>> --
>> 2.9.5
>>