nfsd: add support to CB_NOTIFY for dir attribute changes

If the client requested dir attribute change notifications, send those
alongside any set of add/remove/rename events. Note that the server will
still recall the delegation on a SETATTR, so these are only sent for
changes to child dirents.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
[ cel: folded "nfsd: fix CB_NOTIFY workqueue loop when queue overflows" ]
[ cel: folded "nfsd: recall deleg if a requested dir attr change can't be encoded" ]
Link: https://patch.msgid.link/20260616-dir-deleg-v7-20-6cbc7eac0ade@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>

Documentation/sunrpc/xdr/nfs4_1.x

@@ -464,6 +464,7 @@ pragma public notify_add4;
 struct notify_attr4 {
         notify_entry4   na_changed_entry;
 };
+pragma public notify_attr4;
 
 struct notify_rename4 {
         notify_remove4  nrn_old_entry;

fs/nfsd/nfs4proc.c

@@ -2552,9 +2552,10 @@ nfsd4_verify(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	return status == nfserr_same ? nfs_ok : status;
 }
 
-#define SUPPORTED_NOTIFY_MASK	(BIT(NOTIFY4_REMOVE_ENTRY) |	\
-				 BIT(NOTIFY4_ADD_ENTRY) |	\
-				 BIT(NOTIFY4_RENAME_ENTRY) |	\
+#define SUPPORTED_NOTIFY_MASK	(BIT(NOTIFY4_CHANGE_DIR_ATTRS) |	\
+				 BIT(NOTIFY4_REMOVE_ENTRY) |		\
+				 BIT(NOTIFY4_ADD_ENTRY) |		\
+				 BIT(NOTIFY4_RENAME_ENTRY) |		\
 				 BIT(NOTIFY4_GFLAG_EXTEND))
 
 static __be32

fs/nfsd/nfs4state.c

@@ -3522,10 +3522,15 @@ nfsd4_cb_notify_prepare(struct nfsd4_callback *cb)
 	struct nfsd_notify_event *events[NOTIFY4_EVENT_QUEUE_SIZE];
 	struct xdr_buf xdr = { .buflen = PAGE_SIZE * NOTIFY4_PAGE_ARRAY_SIZE,
 			       .pages  = ncn->ncn_pages };
+	int limit = NOTIFY4_EVENT_QUEUE_SIZE;
 	struct xdr_stream stream;
 	struct nfsd_file *nf;
-	int count, i;
 	bool error = false;
+	int count, i;
+
+	/* Save a slot for dir attr update if requested */
+	if (dp->dl_notify_mask & BIT(NOTIFY4_CHANGE_DIR_ATTRS))
+		--limit;
 
 	/* Clear any failure recorded by a previous transmit. */
 	ncn->ncn_encode_err = false;
@@ -3541,16 +3546,21 @@ nfsd4_cb_notify_prepare(struct nfsd4_callback *cb)
 		return false;
 	}
 
-	/* we can't keep up! */
-	if (count > NOTIFY4_EVENT_QUEUE_SIZE) {
-		spin_unlock(&ncn->ncn_lock);
-		goto out_recall;
-	}
-
 	memcpy(events, ncn->ncn_evt, sizeof(*events) * count);
 	ncn->ncn_evt_cnt = 0;
 	spin_unlock(&ncn->ncn_lock);
 
+	/*
+	 * We can't keep up! Drop the queued events and recall. The queue must
+	 * be drained here: out_recall leaves ncn_evt_cnt at 0, so the release
+	 * op won't see leftover events and requeue this callback forever.
+	 */
+	if (count > limit) {
+		for (i = 0; i < count; ++i)
+			nfsd_notify_event_put(events[i]);
+		goto out_recall;
+	}
+
 	rcu_read_lock();
 	nf = nfsd_file_get(rcu_dereference(dp->dl_stid.sc_file->fi_deleg_file));
 	rcu_read_unlock();
@@ -3588,6 +3598,35 @@ nfsd4_cb_notify_prepare(struct nfsd4_callback *cb)
 put_event:
 		nfsd_notify_event_put(nne);
 	}
+	if (!error && (dp->dl_notify_mask & BIT(NOTIFY4_CHANGE_DIR_ATTRS))) {
+		u32 *maskp = (u32 *)xdr_reserve_space(&stream, sizeof(*maskp));
+		u8 *p;
+
+		if (maskp)
+			p = nfsd4_encode_dir_attr_change(&stream, dp, nf);
+		else
+			p = ERR_PTR(-ENOBUFS);
+
+		if (IS_ERR(p)) {
+			/*
+			 * The client asked to be told about dir attr changes
+			 * but the change could not be encoded. RFC 8881
+			 * s10.9.4 requires the server to recall the delegation
+			 * rather than drop a requested notification, so fall
+			 * through to recall. A NULL return instead means there
+			 * were no attributes to report, so omit the event in
+			 * that case.
+			 */
+			error = true;
+		} else if (p) {
+			*maskp = BIT(NOTIFY4_CHANGE_DIR_ATTRS);
+			ncn->ncn_nf[count].notify_mask.count = 1;
+			ncn->ncn_nf[count].notify_mask.element = maskp;
+			ncn->ncn_nf[count].notify_vals.data = p;
+			ncn->ncn_nf[count].notify_vals.len = (u8 *)stream.p - p;
+			++count;
+		}
+	}
 	if (!error) {
 		ncn->ncn_nf_cnt = count;
 		nfsd_file_put(nf);
@@ -3642,8 +3681,13 @@ nfsd4_cb_notify_release(struct nfsd4_callback *cb)
 	struct nfs4_delegation *dp =
 			container_of(ncn, struct nfs4_delegation, dl_cb_notify);
 
-	/* Drain events that arrived while this callback was in flight */
-	if (READ_ONCE(ncn->ncn_evt_cnt) > 0)
+	/*
+	 * Drain events that arrived while this callback was in flight, but
+	 * don't requeue against a revoked delegation: there's no point in
+	 * notifying a client that no longer holds it, and doing so can pin the
+	 * stid and spin the workqueue.
+	 */
+	if (!dp->dl_stid.sc_status && READ_ONCE(ncn->ncn_evt_cnt) > 0)
 		nfsd4_run_cb_notify(ncn);
 	nfs4_put_stid(&dp->dl_stid);
 }

fs/nfsd/nfs4xdr.c

@@ -4272,11 +4272,12 @@ nfsd4_setup_notify_entry4(struct notify_entry4 *ne, struct xdr_stream *xdr,
 			  struct dentry *dentry, struct nfs4_delegation *dp,
 			  struct nfsd_file *nf, char *name, u32 namelen)
 {
-	struct path path =  { .mnt = nf->nf_file->f_path.mnt,
-			      .dentry = dentry };
+	struct path path = nf->nf_file->f_path;
 	struct nfsd4_fattr_args args = { };
+	const u32 *reqmask;
 	uint32_t *attrmask;
 	__be32 status;
+	bool parent;
 	int ret;
 
 	/* Reserve space for attrmask */
@@ -4288,9 +4289,29 @@ nfsd4_setup_notify_entry4(struct notify_entry4 *ne, struct xdr_stream *xdr,
 	ne->ne_file.len = namelen;
 	ne->ne_attrs.attrmask.element = attrmask;
 
-	/* FIXME: d_find_alias for inode ? */
-	if (!path.dentry || !d_inode(path.dentry))
-		goto noattrs;
+	parent = (dentry == path.dentry);
+	path.dentry = dentry;
+	reqmask = parent ? dp->dl_dir_attrs : dp->dl_child_attrs;
+
+	/*
+	 * A NULL or negative dentry has no attributes to report (expected,
+	 * e.g. for the old entry of a rename or an entry already removed).
+	 * The client may also have been granted the notification while
+	 * requesting no attributes for this entry. Both cases encode an
+	 * empty attribute set rather than failing: the vfs_getattr() and
+	 * nfsd4_encode_attr_vals() failures below recall the delegation, so
+	 * a case with nothing to fetch must short-circuit ahead of them.
+	 */
+	if (!path.dentry || !d_inode(path.dentry) ||
+	    (!reqmask[0] && !reqmask[1])) {
+		attrmask[0] = 0;
+		attrmask[1] = 0;
+		attrmask[2] = 0;
+		ne->ne_attrs.attr_vals.data = NULL;
+		ne->ne_attrs.attr_vals.len = 0;
+		ne->ne_attrs.attrmask.count = 1;
+		return true;
+	}
 
 	/*
 	 * It is possible that the client was granted a delegation when a file
@@ -4299,37 +4320,34 @@ nfsd4_setup_notify_entry4(struct notify_entry4 *ne, struct xdr_stream *xdr,
 	 */
 	ret = vfs_getattr(&path, &args.stat, CB_NOTIFY_STATX_REQUEST_MASK, AT_STATX_SYNC_AS_STAT);
 	if (ret)
-		goto noattrs;
+		return false;
 
 	args.change_attr = nfsd4_change_attribute(&args.stat);
 
-	attrmask[0] = dp->dl_child_attrs[0];
-	attrmask[1] = dp->dl_child_attrs[1];
+	if (parent) {
+		attrmask[0] = dp->dl_dir_attrs[0];
+		attrmask[1] = dp->dl_dir_attrs[1];
+	} else {
+		attrmask[0] = dp->dl_child_attrs[0];
+		attrmask[1] = dp->dl_child_attrs[1];
+
+		if (!setup_notify_fhandle(dentry, dp, nf, &args))
+			attrmask[0] &= ~FATTR4_WORD0_FILEHANDLE;
+
+		if (!(args.stat.result_mask & STATX_BTIME))
+			attrmask[1] &= ~FATTR4_WORD1_TIME_CREATE;
+	}
 	attrmask[2] = 0;
 
-	if (!setup_notify_fhandle(dentry, dp, nf, &args))
-		attrmask[0] &= ~FATTR4_WORD0_FILEHANDLE;
-
-	if (!(args.stat.result_mask & STATX_BTIME))
-		attrmask[1] &= ~FATTR4_WORD1_TIME_CREATE;
-
 	ne->ne_attrs.attrmask.count = 2;
 	ne->ne_attrs.attr_vals.data = (u8 *)xdr->p;
 
 	status = nfsd4_encode_attr_vals(xdr, attrmask, &args);
 	if (status != nfs_ok)
-		goto noattrs;
+		return false;
 
 	ne->ne_attrs.attr_vals.len = (u8 *)xdr->p - ne->ne_attrs.attr_vals.data;
 	return true;
-noattrs:
-	attrmask[0] = 0;
-	attrmask[1] = 0;
-	attrmask[2] = 0;
-	ne->ne_attrs.attr_vals.data = NULL;
-	ne->ne_attrs.attr_vals.len = 0;
-	ne->ne_attrs.attrmask.count = 1;
-	return true;
 }
 
 /**
@@ -4424,6 +4442,42 @@ u8 *nfsd4_encode_notify_event(struct xdr_stream *xdr, struct nfsd_notify_event *
 	return NULL;
 }
 
+/**
+ * nfsd4_encode_dir_attr_change
+ * @xdr: stream to which to encode the fattr4
+ * @dp: delegation where the event occurred
+ * @nf: nfsd_file opened on the directory
+ *
+ * Encode a dir attr change event.
+ *
+ * Return: a pointer to the start of the encoded event on success; NULL
+ * if there were no requested attributes to report, in which case the
+ * caller should omit the event; or an ERR_PTR if the event was requested
+ * but could not be marshalled into @xdr, in which case the caller should
+ * recall the delegation.
+ */
+u8 *nfsd4_encode_dir_attr_change(struct xdr_stream *xdr, struct nfs4_delegation *dp,
+				 struct nfsd_file *nf)
+{
+	struct dentry *dentry = nf->nf_file->f_path.dentry;
+	struct notify_attr4 na = { };
+	u8 *p;
+
+	/* RFC 8881 s10.4.3: ne_file must be a zero-length string for dir attrs */
+	if (!nfsd4_setup_notify_entry4(&na.na_changed_entry, xdr,
+				       dentry, dp, nf, "", 0))
+		return ERR_PTR(-ENOBUFS);
+
+	/* No requested attributes to report; omit the event */
+	if (!na.na_changed_entry.ne_attrs.attr_vals.len)
+		return NULL;
+
+	p = (u8 *)xdr->p;
+	if (!xdrgen_encode_notify_attr4(xdr, &na))
+		return ERR_PTR(-ENOBUFS);
+	return p;
+}
+
 static void svcxdr_init_encode_from_buffer(struct xdr_stream *xdr,
 				struct xdr_buf *buf, __be32 *p, int bytes)
 {

fs/nfsd/nfs4xdr_gen.c

@@ -669,7 +669,7 @@ xdrgen_decode_notify_add4(struct xdr_stream *xdr, struct notify_add4 *ptr)
 	return true;
 }
 
-static bool __maybe_unused
+bool
 xdrgen_decode_notify_attr4(struct xdr_stream *xdr, struct notify_attr4 *ptr)
 {
 	if (!xdrgen_decode_notify_entry4(xdr, &ptr->na_changed_entry))
@@ -1091,7 +1091,7 @@ xdrgen_encode_notify_add4(struct xdr_stream *xdr, const struct notify_add4 *valu
 	return true;
 }
 
-static bool __maybe_unused
+bool
 xdrgen_encode_notify_attr4(struct xdr_stream *xdr, const struct notify_attr4 *value)
 {
 	if (!xdrgen_encode_notify_entry4(xdr, &value->na_changed_entry))

fs/nfsd/nfs4xdr_gen.h

@@ -38,6 +38,9 @@ bool xdrgen_encode_notify_remove4(struct xdr_stream *xdr, const struct notify_re
 bool xdrgen_decode_notify_add4(struct xdr_stream *xdr, struct notify_add4 *ptr);
 bool xdrgen_encode_notify_add4(struct xdr_stream *xdr, const struct notify_add4 *value);
 
+bool xdrgen_decode_notify_attr4(struct xdr_stream *xdr, struct notify_attr4 *ptr);
+bool xdrgen_encode_notify_attr4(struct xdr_stream *xdr, const struct notify_attr4 *value);
+
 bool xdrgen_decode_notify_rename4(struct xdr_stream *xdr, struct notify_rename4 *ptr);
 bool xdrgen_encode_notify_rename4(struct xdr_stream *xdr, const struct notify_rename4 *value);
 

fs/nfsd/xdr4.h

@@ -973,6 +973,8 @@ __be32 nfsd4_encode_fattr_to_buf(__be32 **p, int words,
 u8 *nfsd4_encode_notify_event(struct xdr_stream *xdr, struct nfsd_notify_event *nne,
 			      struct nfs4_delegation *dd, struct nfsd_file *nf,
 			      u32 *notify_mask);
+u8 *nfsd4_encode_dir_attr_change(struct xdr_stream *xdr, struct nfs4_delegation *dp,
+				 struct nfsd_file *nf);
 extern __be32 nfsd4_setclientid(struct svc_rqst *rqstp,
 		struct nfsd4_compound_state *, union nfsd4_op_u *u);
 extern __be32 nfsd4_setclientid_confirm(struct svc_rqst *rqstp,