rbd: don't allocate mon_addrs buffer in rbd_add()

The mon_addrs buffer in rbd_add is used to hold a copy of the
monitor IP addresses supplied via /sys/bus/rbd/add.  That is
passed to rbd_get_client(), which never modifies it (nor do
any of the functions it gets passed to thereafter)--the mon_addr
parameter to rbd_get_client() is a pointer to constant data, so it
can't be modifed.  Furthermore, rbd_get_client() has the length of
the mon_addrs buffer and that is used to ensure nothing goes beyond
its end.

Based on all this, there is no reason that a buffer needs to
be used to hold a copy of the mon_addrs provided via
/sys/bus/rbd/add.   Instead, the location within that passed-in
buffer can be provided, along with the length of the "token"
therein which represents the monitor IP's.

A small change to rbd_add_parse_args() allows the address within the
buffer to be passed back, and the length is already returned.  This
now means that, at least from the perspective of this interface,
there is no such thing as a list of monitor addresses that is too
long.
Signed-off-by: Alex Elder <elder@dreamhost.com>

drivers/block/rbd.c

@@ -2284,7 +2284,7 @@ static inline size_t copy_token(const char **buf,
  */
 static int rbd_add_parse_args(struct rbd_device *rbd_dev,
 			      const char *buf,
-			      char *mon_addrs,
+			      const char **mon_addrs,
 			      size_t *mon_addrs_size,
 			      char *options,
 			      size_t options_size)
@@ -2293,10 +2293,13 @@ static int rbd_add_parse_args(struct rbd_device *rbd_dev,
 
 	/* The first four tokens are required */
 
-	len = copy_token(&buf, mon_addrs, *mon_addrs_size);
-	if (!len || len >= *mon_addrs_size)
+	len = next_token(&buf);
+	if (!len)
 		return -EINVAL;
 	*mon_addrs_size = len + 1;
+	*mon_addrs = buf;
+
+	buf += len;
 
 	len = copy_token(&buf, options, options_size);
 	if (!len || len >= options_size)
@@ -2337,8 +2340,8 @@ static ssize_t rbd_add(struct bus_type *bus,
 		       size_t count)
 {
 	struct rbd_device *rbd_dev;
-	char *mon_addrs = NULL;
-	size_t mon_addrs_size;
+	const char *mon_addrs = NULL;
+	size_t mon_addrs_size = 0;
 	char *options = NULL;
 	struct ceph_osd_client *osdc;
 	int rc = -ENOMEM;
@@ -2349,9 +2352,6 @@ static ssize_t rbd_add(struct bus_type *bus,
 	rbd_dev = kzalloc(sizeof(*rbd_dev), GFP_KERNEL);
 	if (!rbd_dev)
 		goto err_nomem;
-	mon_addrs = kmalloc(count, GFP_KERNEL);
-	if (!mon_addrs)
-		goto err_nomem;
 	options = kmalloc(count, GFP_KERNEL);
 	if (!options)
 		goto err_nomem;
@@ -2372,8 +2372,7 @@ static ssize_t rbd_add(struct bus_type *bus,
 	sprintf(rbd_dev->name, "%s%d", RBD_DRV_NAME, rbd_dev->id);
 
 	/* parse add command */
-	mon_addrs_size = count;
-	rc = rbd_add_parse_args(rbd_dev, buf, mon_addrs, &mon_addrs_size,
+	rc = rbd_add_parse_args(rbd_dev, buf, &mon_addrs, &mon_addrs_size,
 				options, count);
 	if (rc)
 		goto err_put_id;
@@ -2420,7 +2419,6 @@ static ssize_t rbd_add(struct bus_type *bus,
 
 	rbd_bus_del_dev(rbd_dev);
 	kfree(options);
-	kfree(mon_addrs);
 	return rc;
 
 err_out_blkdev:
@@ -2431,7 +2429,6 @@ static ssize_t rbd_add(struct bus_type *bus,
 	rbd_id_put(rbd_dev);
 err_nomem:
 	kfree(options);
-	kfree(mon_addrs);
 	kfree(rbd_dev);
 
 	dout("Error adding device %s\n", buf);