[PATCH RFC 23/24] nfs: optionally request a delegation on GETATTR

[Jeff Layton <jlayton@kernel.org>]

We expect directory delegations to most helpful when their children have
frequently revalidated dentries. The way we usually revalidate them is
to check that the dentry's d_time field matches the change attribute on
the parent. Most dentry revalidations that have to issue an RPC end up
as a GETATTR on the wire for the parent, if the parent hasn't changed,
then the dentry is fine.

Add a new NFS_INO_GDD_GETATTR flag to the nfsi->flags field. Whenever we
validate a dentry vs. its parent, set that flag on the parent.  Then,
when we next do a GETATTR vs. the parent, test and clear the flag and do
a GDD_GETATTR if it was set. If the the GET_DIR_DELEGATION succeeds, set
the delegation in the inode.

Finally, a lot of servers don't support GET_DIR_DELEGATION, so add a
NFS_CAP_* bit to track whether the server supports it, and enable it by
default on v4.1+, and retry without a delegation if we get back an
ENOTSUPP.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/nfs/delegation.c       |  1 +
 fs/nfs/dir.c              |  8 ++++++++
 fs/nfs/nfs4proc.c         | 45 ++++++++++++++++++++++++++++++++++++++++++---
 include/linux/nfs_fs.h    |  1 +
 include/linux/nfs_fs_sb.h |  1 +
 5 files changed, 53 insertions(+), 3 deletions(-)

diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
index 88dbec4739d3..14c14bd03465 100644
--- a/fs/nfs/delegation.c
+++ b/fs/nfs/delegation.c
@@ -356,6 +356,7 @@ nfs_detach_delegation_locked(struct nfs_inode *nfsi,
 	delegation->inode = NULL;
 	rcu_assign_pointer(nfsi->delegation, NULL);
 	spin_unlock(&delegation->lock);
+	clear_bit(NFS_INO_GDD_GETATTR, &nfsi->flags);
 	return delegation;
 }
 
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 061648c73116..930fe7e14914 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1504,12 +1504,20 @@ static int nfs_dentry_verify_change(struct inode *dir, struct dentry *dentry)
 static int nfs_check_verifier(struct inode *dir, struct dentry *dentry,
 			      int rcu_walk)
 {
+	struct nfs_inode *nfsi = NFS_I(dir);
+
 	if (IS_ROOT(dentry))
 		return 1;
 	if (NFS_SERVER(dir)->flags & NFS_MOUNT_LOOKUP_CACHE_NONE)
 		return 0;
 	if (!nfs_dentry_verify_change(dir, dentry))
 		return 0;
+	/*
+	 * The dentry matches the directory's change attribute, so
+	 * we're likely revalidating here. Flag the dir so that we
+	 * ask for a delegation on the next getattr.
+	 */
+	set_bit(NFS_INO_GDD_GETATTR, &nfsi->flags);
 	/* Revalidate nfsi->cache_change_attribute before we declare a match */
 	if (nfs_mapping_need_revalidate_inode(dir)) {
 		if (rcu_walk)
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index d518388bd0d6..3dbe9a18c9be 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -4318,6 +4318,21 @@ static int nfs4_get_referral(struct rpc_clnt *client, struct inode *dir,
 	return status;
 }
 
+static bool should_request_dir_deleg(struct inode *inode)
+{
+	if (!inode)
+		return false;
+	if (!S_ISDIR(inode->i_mode))
+		return false;
+	if (!nfs_server_capable(inode, NFS_CAP_GET_DIR_DELEG))
+		return false;
+	if (!test_and_clear_bit(NFS_INO_GDD_GETATTR, &(NFS_I(inode)->flags)))
+		return false;
+	if (nfs4_have_delegation(inode, FMODE_READ))
+		return false;
+	return true;
+}
+
 static int _nfs4_proc_getattr(struct nfs_server *server, struct nfs_fh *fhandle,
 				struct nfs_fattr *fattr, struct inode *inode)
 {
@@ -4331,11 +4346,12 @@ static int _nfs4_proc_getattr(struct nfs_server *server, struct nfs_fh *fhandle,
 		.server = server,
 	};
 	struct rpc_message msg = {
-		.rpc_proc = &nfs4_procedures[NFSPROC4_CLNT_GETATTR],
 		.rpc_argp = &args,
 		.rpc_resp = &res,
 	};
 	unsigned short task_flags = 0;
+	bool gdd;
+	int status;
 
 	if (nfs4_has_session(server->nfs_client))
 		task_flags = RPC_TASK_MOVEABLE;
@@ -4344,11 +4360,32 @@ static int _nfs4_proc_getattr(struct nfs_server *server, struct nfs_fh *fhandle,
 	if (inode && (server->flags & NFS_MOUNT_SOFTREVAL))
 		task_flags |= RPC_TASK_TIMEOUT;
 
+retry:
+	gdd = should_request_dir_deleg(inode);
+	if (gdd)
+		msg.rpc_proc = &nfs4_procedures[NFSPROC4_CLNT_GDD_GETATTR];
+	else
+		msg.rpc_proc = &nfs4_procedures[NFSPROC4_CLNT_GETATTR];
+
 	nfs4_bitmap_copy_adjust(bitmask, nfs4_bitmask(server, fattr->label), inode, 0);
 	nfs_fattr_init(fattr);
 	nfs4_init_sequence(&args.seq_args, &res.seq_res, 0, 0);
-	return nfs4_do_call_sync(server->client, server, &msg,
-			&args.seq_args, &res.seq_res, task_flags);
+	status = nfs4_do_call_sync(server->client, server, &msg,
+				   &args.seq_args, &res.seq_res, task_flags);
+	switch (status) {
+	case 0:
+		if (gdd && res.nf_status == GDD4_OK)
+			status = nfs_inode_set_delegation(inode, current_cred(), FMODE_READ,
+							  &res.deleg, 0);
+		break;
+	case -ENOTSUPP:
+		/* If the server doesn't support GET_DIR_DELEGATION, retry without it */
+		if (gdd) {
+			server->caps &= ~NFS_CAP_GET_DIR_DELEG;
+			goto retry;
+		}
+	}
+	return status;
 }
 
 int nfs4_proc_getattr(struct nfs_server *server, struct nfs_fh *fhandle,
@@ -10552,6 +10589,7 @@ static const struct nfs4_minor_version_ops nfs_v4_1_minor_ops = {
 	.minor_version = 1,
 	.init_caps = NFS_CAP_READDIRPLUS
 		| NFS_CAP_ATOMIC_OPEN
+		| NFS_CAP_GET_DIR_DELEG
 		| NFS_CAP_POSIX_LOCK
 		| NFS_CAP_STATEID_NFSV41
 		| NFS_CAP_ATOMIC_OPEN_V1
@@ -10578,6 +10616,7 @@ static const struct nfs4_minor_version_ops nfs_v4_2_minor_ops = {
 	.minor_version = 2,
 	.init_caps = NFS_CAP_READDIRPLUS
 		| NFS_CAP_ATOMIC_OPEN
+		| NFS_CAP_GET_DIR_DELEG
 		| NFS_CAP_POSIX_LOCK
 		| NFS_CAP_STATEID_NFSV41
 		| NFS_CAP_ATOMIC_OPEN_V1
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index f5ce7b101146..5140e4dac98a 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -318,6 +318,7 @@ struct nfs4_copy_state {
 #define NFS_INO_LAYOUTCOMMITTING (10)		/* layoutcommit inflight */
 #define NFS_INO_LAYOUTSTATS	(11)		/* layoutstats inflight */
 #define NFS_INO_ODIRECT		(12)		/* I/O setting is O_DIRECT */
+#define NFS_INO_GDD_GETATTR	(13)		/* Ask for dir deleg on next GETATTR */
 
 static inline struct nfs_inode *NFS_I(const struct inode *inode)
 {
diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index 92de074e63b9..0ab744cf52d7 100644
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -278,6 +278,7 @@ struct nfs_server {
 #define NFS_CAP_LGOPEN		(1U << 5)
 #define NFS_CAP_CASE_INSENSITIVE	(1U << 6)
 #define NFS_CAP_CASE_PRESERVING	(1U << 7)
+#define NFS_CAP_GET_DIR_DELEG	(1U << 13)
 #define NFS_CAP_POSIX_LOCK	(1U << 14)
 #define NFS_CAP_UIDGID_NOMAP	(1U << 15)
 #define NFS_CAP_STATEID_NFSV41	(1U << 16)

-- 
2.44.0