ceph: add flag to designate that a request is asynchronous

...and ensure that such requests are never queued. The MDS has need to
know that a request is asynchronous so add flags and proper
infrastructure for that.

Also, delegated inode numbers and directory caps are associated with the
session, so ensure that async requests are always transmitted on the
first attempt and are never queued to wait for session reestablishment.

If it does end up looking like we'll need to queue the request, then
have it return -EJUKEBOX so the caller can reattempt with a synchronous
request.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/inode.c

@@ -1311,6 +1311,7 @@ int ceph_fill_trace(struct super_block *sb, struct ceph_mds_request *req)
 		err = fill_inode(in, req->r_locked_page, &rinfo->targeti, NULL,
 				session,
 				(!test_bit(CEPH_MDS_R_ABORTED, &req->r_req_flags) &&
+				 !test_bit(CEPH_MDS_R_ASYNC, &req->r_req_flags) &&
 				 rinfo->head->result == 0) ?  req->r_fmode : -1,
 				&req->r_caps_reservation);
 		if (err < 0) {

fs/ceph/mds_client.c

@@ -2528,6 +2528,8 @@ static int __prepare_send_request(struct ceph_mds_client *mdsc,
 	rhead->oldest_client_tid = cpu_to_le64(__get_oldest_tid(mdsc));
 	if (test_bit(CEPH_MDS_R_GOT_UNSAFE, &req->r_req_flags))
 		flags |= CEPH_MDS_FLAG_REPLAY;
+	if (test_bit(CEPH_MDS_R_ASYNC, &req->r_req_flags))
+		flags |= CEPH_MDS_FLAG_ASYNC;
 	if (req->r_parent)
 		flags |= CEPH_MDS_FLAG_WANT_DENTRY;
 	rhead->flags = cpu_to_le32(flags);
@@ -2611,6 +2613,10 @@ static void __do_request(struct ceph_mds_client *mdsc,
 	mds = __choose_mds(mdsc, req, &random);
 	if (mds < 0 ||
 	    ceph_mdsmap_get_state(mdsc->mdsmap, mds) < CEPH_MDS_STATE_ACTIVE) {
+		if (test_bit(CEPH_MDS_R_ASYNC, &req->r_req_flags)) {
+			err = -EJUKEBOX;
+			goto finish;
+		}
 		dout("do_request no mds or not active, waiting for map\n");
 		list_add(&req->r_wait, &mdsc->waiting_for_map);
 		return;
@@ -2635,6 +2641,15 @@ static void __do_request(struct ceph_mds_client *mdsc,
 			err = -EACCES;
 			goto out_session;
 		}
+		/*
+		 * We cannot queue async requests since the caps and delegated
+		 * inodes are bound to the session. Just return -EJUKEBOX and
+		 * let the caller retry a sync request in that case.
+		 */
+		if (test_bit(CEPH_MDS_R_ASYNC, &req->r_req_flags)) {
+			err = -EJUKEBOX;
+			goto out_session;
+		}
 		if (session->s_state == CEPH_MDS_SESSION_NEW ||
 		    session->s_state == CEPH_MDS_SESSION_CLOSING) {
 			__open_session(mdsc, session);

fs/ceph/mds_client.h

@@ -255,6 +255,7 @@ struct ceph_mds_request {
 #define CEPH_MDS_R_GOT_RESULT		(5) /* got a result */
 #define CEPH_MDS_R_DID_PREPOPULATE	(6) /* prepopulated readdir */
 #define CEPH_MDS_R_PARENT_LOCKED	(7) /* is r_parent->i_rwsem wlocked? */
+#define CEPH_MDS_R_ASYNC		(8) /* async request */
 	unsigned long	r_req_flags;
 
 	struct mutex r_fill_mutex;

include/linux/ceph/ceph_fs.h

@@ -444,8 +444,9 @@ union ceph_mds_request_args {
 	} __attribute__ ((packed)) lookupino;
 } __attribute__ ((packed));
 
-#define CEPH_MDS_FLAG_REPLAY        1  /* this is a replayed op */
-#define CEPH_MDS_FLAG_WANT_DENTRY   2  /* want dentry in reply */
+#define CEPH_MDS_FLAG_REPLAY		1 /* this is a replayed op */
+#define CEPH_MDS_FLAG_WANT_DENTRY	2 /* want dentry in reply */
+#define CEPH_MDS_FLAG_ASYNC		4 /* request is asynchronous */
 
 struct ceph_mds_request_head {
 	__le64 oldest_client_tid;