[PATCH] ceph: use a flexible array for monitor addresses

[Rosen Penev]

ceph_alloc_options() allocates the monitor address array separately,
always sized for CEPH_MAX_MON entries. Make it a flexible array member
at the end of struct ceph_options and allocate both together with
kzalloc_flex(). The array was already an 8 KiB slab object, so this
only drops the separate allocation and its error path.

num_mon is the number of addresses in use, not the capacity, so the
array cannot be annotated with __counted_by().

ceph_compare_options() memcmp()s the simple fields up to the first
member that needs a custom comparison. With mon_addr gone from there,
use num_mon as that boundary; the compared fields are unchanged.
Document that num_mon has to stay first past that point.

Assisted-by: LLM
Signed-off-by: Rosen Penev <rosenp@xxxxxxxxx>
---
 include/linux/ceph/libceph.h |  7 ++++---
 net/ceph/ceph_common.c       | 11 ++---------
 2 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/include/linux/ceph/libceph.h b/include/linux/ceph/libceph.h
index f92fdd853f1f..e585d6d11303 100644
--- a/include/linux/ceph/libceph.h
+++ b/include/linux/ceph/libceph.h
@@ -57,15 +57,16 @@ struct ceph_options {
 	/*
 	 * any type that can't be simply compared or doesn't need
 	 * to be compared should go beyond this point,
-	 * ceph_compare_options() should be updated accordingly
+	 * ceph_compare_options() should be updated accordingly.
+	 * num_mon must stay the first member past this point, as
+	 * ceph_compare_options() uses it as the end of the memcmp().
 	 */
 
-	struct ceph_entity_addr *mon_addr; /* should be the first
-					      pointer type of args */
 	int num_mon;
 	char *name;
 	struct ceph_crypto_key *key;
 	struct rb_root crush_locs;
+	struct ceph_entity_addr mon_addr[];
 };
 
 /*
diff --git a/net/ceph/ceph_common.c b/net/ceph/ceph_common.c
index a797c7360e3c..95dc18257056 100644
--- a/net/ceph/ceph_common.c
+++ b/net/ceph/ceph_common.c
@@ -133,7 +133,7 @@ int ceph_compare_options(struct ceph_options *new_opt,
 {
 	struct ceph_options *opt1 = new_opt;
 	struct ceph_options *opt2 = client->options;
-	int ofs = offsetof(struct ceph_options, mon_addr);
+	int ofs = offsetof(struct ceph_options, num_mon);
 	int i;
 	int ret;
 
@@ -309,17 +309,11 @@ struct ceph_options *ceph_alloc_options(void)
 {
 	struct ceph_options *opt;
 
-	opt = kzalloc_obj(*opt);
+	opt = kzalloc_flex(*opt, mon_addr, CEPH_MAX_MON);
 	if (!opt)
 		return NULL;
 
 	opt->crush_locs = RB_ROOT;
-	opt->mon_addr = kzalloc_objs(*opt->mon_addr, CEPH_MAX_MON);
-	if (!opt->mon_addr) {
-		kfree(opt);
-		return NULL;
-	}
-
 	opt->flags = CEPH_OPT_DEFAULT;
 	opt->osd_keepalive_timeout = CEPH_OSD_KEEPALIVE_DEFAULT;
 	opt->mount_timeout = CEPH_MOUNT_TIMEOUT_DEFAULT;
@@ -344,7 +338,6 @@ void ceph_destroy_options(struct ceph_options *opt)
 		ceph_crypto_key_destroy(opt->key);
 		kfree(opt->key);
 	}
-	kfree(opt->mon_addr);
 	kfree(opt);
 }
 EXPORT_SYMBOL(ceph_destroy_options);
-- 
2.56.0