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Date:   Mon, 15 May 2023 13:15:09 -0700
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Subject: Re: [PATCH v2 4/4] NFSD: handle GETATTR conflict with write
 delegation
Content-Language: en-US
To:     Jeff Layton <jlayton@kernel.org>,
        Olga Kornievskaia <aglo@umich.edu>
Cc:     chuck.lever@oracle.com, 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 11:58 AM, Jeff Layton wrote:
> On Mon, 2023-05-15 at 11:26 -0700, dai.ngo@oracle.com wrote:
>> 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.
>>
>
>
>  From RFC 8881 10.4.3:
>
> "It should be noted that the server is under no obligation to use
> CB_GETATTR, and therefore the server MAY simply recall the delegation to
> avoid its use."
>
> As I see it, the main benefit is that you avoid having to recall a write
> delegation when someone does a drive-by stat() on the file (e.g. due to
> a "ls -l" in its parent directory).

Yes, that's right I forgot to mention this. If we don't want to recall the
write delegation then we have to support CB_GETATTR.

Thanks,
-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
>>>>