libceph: support for balanced and localized reads

OSD-side issues with reads from replica have been resolved in
Octopus.  Reading from replica should be safe wrt. unstable or
uncommitted state now, so add support for balanced and localized
reads.

There are two cases when a read from replica can't be served:

- OSD may silently drop the request, expecting the client to
  notice that the acting set has changed and resend via the usual
  means (handled with t->used_replica)

- OSD may return EAGAIN, expecting the client to resend to the
  primary, ignoring replica read flags (see handle_reply())

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>

2 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/ceph/osd_client.h b/include/linux/ceph/osd_client.h
index 734f7c6a9f56..671fb93e8c60 100644
--- a/include/linux/ceph/osd_client.h
+++ b/include/linux/ceph/osd_client.h
@@ -165,6 +165,7 @@ struct ceph_osd_request_target {
 	bool recovery_deletes;
 
 	unsigned int flags;                /* CEPH_OSD_FLAG_* */
+	bool used_replica;
 	bool paused;
 
 	u32 epoch;
diff --git a/include/linux/ceph/osdmap.h b/include/linux/ceph/osdmap.h
index 8c9d18cc9f45..3f4498fef6ad 100644
--- a/include/linux/ceph/osdmap.h
+++ b/include/linux/ceph/osdmap.h
@@ -317,6 +317,9 @@ int ceph_parse_crush_location(char *crush_location, struct rb_root *locs);
 int ceph_compare_crush_locs(struct rb_root *locs1, struct rb_root *locs2);
 void ceph_clear_crush_locs(struct rb_root *locs);
 
+int ceph_get_crush_locality(struct ceph_osdmap *osdmap, int id,
+			    struct rb_root *locs);
+
 extern struct ceph_pg_pool_info *ceph_pg_pool_by_id(struct ceph_osdmap *map,
 						    u64 id);
 extern const char *ceph_pg_pool_name_by_id(struct ceph_osdmap *map, u64 id);