ceph: add possible_max_rank and make the code more readable

The m_num_mds here is actually the number for MDSs which are in
up:active status, and it will be duplicated to m_num_active_mds,
so remove it.

Add possible_max_rank to the mdsmap struct and this will be
the correctly possible largest rank boundary.

Remove the special case for one mds in __mdsmap_get_random_mds(),
because the validate mds rank may not always be 0.
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/debugfs.c

@@ -33,7 +33,7 @@ static int mdsmap_show(struct seq_file *s, void *p)
 	seq_printf(s, "max_mds %d\n", mdsmap->m_max_mds);
 	seq_printf(s, "session_timeout %d\n", mdsmap->m_session_timeout);
 	seq_printf(s, "session_autoclose %d\n", mdsmap->m_session_autoclose);
-	for (i = 0; i < mdsmap->m_num_mds; i++) {
+	for (i = 0; i < mdsmap->possible_max_rank; i++) {
 		struct ceph_entity_addr *addr = &mdsmap->m_info[i].addr;
 		int state = mdsmap->m_info[i].state;
 		seq_printf(s, "\tmds%d\t%s\t(%s)\n", i,

fs/ceph/mds_client.c

@@ -598,7 +598,7 @@ static struct ceph_mds_session *register_session(struct ceph_mds_client *mdsc,
 {
 	struct ceph_mds_session *s;
 
-	if (mds >= mdsc->mdsmap->m_num_mds)
+	if (mds >= mdsc->mdsmap->possible_max_rank)
 		return ERR_PTR(-EINVAL);
 
 	s = kzalloc(sizeof(*s), GFP_NOFS);
@@ -1231,7 +1231,7 @@ static void __open_export_target_sessions(struct ceph_mds_client *mdsc,
 	struct ceph_mds_session *ts;
 	int i, mds = session->s_mds;
 
-	if (mds >= mdsc->mdsmap->m_num_mds)
+	if (mds >= mdsc->mdsmap->possible_max_rank)
 		return;
 
 	mi = &mdsc->mdsmap->m_info[mds];
@@ -3785,7 +3785,7 @@ static void check_new_map(struct ceph_mds_client *mdsc,
 	dout("check_new_map new %u old %u\n",
 	     newmap->m_epoch, oldmap->m_epoch);
 
-	for (i = 0; i < oldmap->m_num_mds && i < mdsc->max_sessions; i++) {
+	for (i = 0; i < oldmap->possible_max_rank && i < mdsc->max_sessions; i++) {
 		if (!mdsc->sessions[i])
 			continue;
 		s = mdsc->sessions[i];
@@ -3799,7 +3799,7 @@ static void check_new_map(struct ceph_mds_client *mdsc,
 		     ceph_mdsmap_is_laggy(newmap, i) ? " (laggy)" : "",
 		     ceph_session_state_name(s->s_state));
 
-		if (i >= newmap->m_num_mds) {
+		if (i >= newmap->possible_max_rank) {
 			/* force close session for stopped mds */
 			get_session(s);
 			__unregister_session(mdsc, s);
@@ -3856,7 +3856,7 @@ static void check_new_map(struct ceph_mds_client *mdsc,
 		}
 	}
 
-	for (i = 0; i < newmap->m_num_mds && i < mdsc->max_sessions; i++) {
+	for (i = 0; i < newmap->possible_max_rank && i < mdsc->max_sessions; i++) {
 		s = mdsc->sessions[i];
 		if (!s)
 			continue;

fs/ceph/mdsmap.c

@@ -14,22 +14,15 @@
 #include "super.h"
 
 #define CEPH_MDS_IS_READY(i, ignore_laggy) \
-	(m->m_info[i].state > 0 && (ignore_laggy ? true : !m->m_info[i].laggy))
+	(m->m_info[i].state > 0 && ignore_laggy ? true : !m->m_info[i].laggy)
 
 static int __mdsmap_get_random_mds(struct ceph_mdsmap *m, bool ignore_laggy)
 {
 	int n = 0;
 	int i, j;
 
-	/*
-	 * special case for one mds, no matter it is laggy or
-	 * not we have no choice
-	 */
-	if (1 == m->m_num_mds && m->m_info[0].state > 0)
-		return 0;
-
 	/* count */
-	for (i = 0; i < m->m_num_mds; i++)
+	for (i = 0; i < m->possible_max_rank; i++)
 		if (CEPH_MDS_IS_READY(i, ignore_laggy))
 			n++;
 	if (n == 0)
@@ -37,7 +30,7 @@ static int __mdsmap_get_random_mds(struct ceph_mdsmap *m, bool ignore_laggy)
 
 	/* pick */
 	n = prandom_u32() % n;
-	for (j = 0, i = 0; i < m->m_num_mds; i++) {
+	for (j = 0, i = 0; i < m->possible_max_rank; i++) {
 		if (CEPH_MDS_IS_READY(i, ignore_laggy))
 			j++;
 		if (j > n)
@@ -55,10 +48,10 @@ int ceph_mdsmap_get_random_mds(struct ceph_mdsmap *m)
 	int mds;
 
 	mds = __mdsmap_get_random_mds(m, false);
-	if (mds == m->m_num_mds || mds == -1)
+	if (mds == m->possible_max_rank || mds == -1)
 		mds = __mdsmap_get_random_mds(m, true);
 
-	return mds == m->m_num_mds ? -1 : mds;
+	return mds == m->possible_max_rank ? -1 : mds;
 }
 
 #define __decode_and_drop_type(p, end, type, bad)		\
@@ -129,7 +122,6 @@ struct ceph_mdsmap *ceph_mdsmap_decode(void **p, void *end)
 	int err;
 	u8 mdsmap_v, mdsmap_cv;
 	u16 mdsmap_ev;
-	u32 possible_max_rank;
 
 	m = kzalloc(sizeof(*m), GFP_NOFS);
 	if (!m)
@@ -157,24 +149,23 @@ struct ceph_mdsmap *ceph_mdsmap_decode(void **p, void *end)
 	m->m_max_mds = ceph_decode_32(p);
 
 	/*
-	 * pick out the active nodes as the m_num_mds, the m_num_mds
-	 * maybe larger than m_max_mds when decreasing the max_mds in
-	 * cluster side, in other case it should less than or equal
-	 * to m_max_mds.
+	 * pick out the active nodes as the m_num_active_mds, the
+	 * m_num_active_mds maybe larger than m_max_mds when decreasing
+	 * the max_mds in cluster side, in other case it should less
+	 * than or equal to m_max_mds.
 	 */
-	m->m_num_mds = n = ceph_decode_32(p);
-	m->m_num_active_mds = m->m_num_mds;
+	m->m_num_active_mds = n = ceph_decode_32(p);
 
 	/*
-	 * the possible max rank, it maybe larger than the m->m_num_mds,
+	 * the possible max rank, it maybe larger than the m_num_active_mds,
 	 * for example if the mds_max == 2 in the cluster, when the MDS(0)
 	 * was laggy and being replaced by a new MDS, we will temporarily
 	 * receive a new mds map with n_num_mds == 1 and the active MDS(1),
-	 * and the mds rank >= m->m_num_mds.
+	 * and the mds rank >= m_num_active_mds.
 	 */
-	possible_max_rank = max((u32)m->m_num_mds, m->m_max_mds);
+	m->possible_max_rank = max(m->m_num_active_mds, m->m_max_mds);
 
-	m->m_info = kcalloc(m->m_num_mds, sizeof(*m->m_info), GFP_NOFS);
+	m->m_info = kcalloc(m->possible_max_rank, sizeof(*m->m_info), GFP_NOFS);
 	if (!m->m_info)
 		goto nomem;
 
@@ -248,7 +239,7 @@ struct ceph_mdsmap *ceph_mdsmap_decode(void **p, void *end)
 		     ceph_mds_state_name(state),
 		     laggy ? "(laggy)" : "");
 
-		if (mds < 0 || mds >= possible_max_rank) {
+		if (mds < 0 || mds >= m->possible_max_rank) {
 			pr_warn("mdsmap_decode got incorrect mds(%d)\n", mds);
 			continue;
 		}
@@ -318,14 +309,14 @@ struct ceph_mdsmap *ceph_mdsmap_decode(void **p, void *end)
 
 		for (i = 0; i < n; i++) {
 			s32 mds = ceph_decode_32(p);
-			if (mds >= 0 && mds < m->m_num_mds) {
+			if (mds >= 0 && mds < m->possible_max_rank) {
 				if (m->m_info[mds].laggy)
 					num_laggy++;
 			}
 		}
 		m->m_num_laggy = num_laggy;
 
-		if (n > m->m_num_mds) {
+		if (n > m->possible_max_rank) {
 			void *new_m_info = krealloc(m->m_info,
 						    n * sizeof(*m->m_info),
 						    GFP_NOFS | __GFP_ZERO);
@@ -333,7 +324,7 @@ struct ceph_mdsmap *ceph_mdsmap_decode(void **p, void *end)
 				goto nomem;
 			m->m_info = new_m_info;
 		}
-		m->m_num_mds = n;
+		m->possible_max_rank = n;
 	}
 
 	/* inc */
@@ -404,7 +395,7 @@ void ceph_mdsmap_destroy(struct ceph_mdsmap *m)
 {
 	int i;
 
-	for (i = 0; i < m->m_num_mds; i++)
+	for (i = 0; i < m->possible_max_rank; i++)
 		kfree(m->m_info[i].export_targets);
 	kfree(m->m_info);
 	kfree(m->m_data_pg_pools);
@@ -420,7 +411,7 @@ bool ceph_mdsmap_is_cluster_available(struct ceph_mdsmap *m)
 		return false;
 	if (m->m_num_laggy == m->m_num_active_mds)
 		return false;
-	for (i = 0; i < m->m_num_mds; i++) {
+	for (i = 0; i < m->possible_max_rank; i++) {
 		if (m->m_info[i].state == CEPH_MDS_STATE_ACTIVE)
 			nr_active++;
 	}

include/linux/ceph/mdsmap.h

@@ -26,8 +26,8 @@ struct ceph_mdsmap {
 	u32 m_session_autoclose;        /* seconds */
 	u64 m_max_file_size;
 	u32 m_max_mds;			/* expected up:active mds number */
-	int m_num_active_mds;		/* actual up:active mds number */
-	int m_num_mds;                  /* size of m_info array */
+	u32 m_num_active_mds;		/* actual up:active mds number */
+	u32 possible_max_rank;		/* possible max rank index */
 	struct ceph_mds_info *m_info;
 
 	/* which object pools file data can be stored in */
@@ -43,7 +43,7 @@ struct ceph_mdsmap {
 static inline struct ceph_entity_addr *
 ceph_mdsmap_get_addr(struct ceph_mdsmap *m, int w)
 {
-	if (w >= m->m_num_mds)
+	if (w >= m->possible_max_rank)
 		return NULL;
 	return &m->m_info[w].addr;
 }
@@ -51,14 +51,14 @@ ceph_mdsmap_get_addr(struct ceph_mdsmap *m, int w)
 static inline int ceph_mdsmap_get_state(struct ceph_mdsmap *m, int w)
 {
 	BUG_ON(w < 0);
-	if (w >= m->m_num_mds)
+	if (w >= m->possible_max_rank)
 		return CEPH_MDS_STATE_DNE;
 	return m->m_info[w].state;
 }
 
 static inline bool ceph_mdsmap_is_laggy(struct ceph_mdsmap *m, int w)
 {
-	if (w >= 0 && w < m->m_num_mds)
+	if (w >= 0 && w < m->possible_max_rank)
 		return m->m_info[w].laggy;
 	return false;
 }