rbd: define rbd_dev_image_id()

New format 2 rbd images are permanently identified by a unique image
id.  Each rbd image also has a name, but the name can be changed.
A format 2 rbd image will have an object--whose name is based on the
image name--which maps an image's name to its image id.

Create a new function rbd_dev_image_id() that checks for the
existence of the image id object, and if it's found, records the
image id in the rbd_device structure.

Create a new rbd device attribute (/sys/bus/rbd/<num>/image_id) that
makes this information available.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

1 files changed, 100 insertions, 0 deletions

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index b8956131950c..34f46c3b188f 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -66,6 +66,8 @@
 
 #define RBD_SNAP_HEAD_NAME      "-"
 
+#define RBD_IMAGE_ID_LEN_MAX    64
+
 /*
  * An RBD device name will be "rbd#", where the "rbd" comes from
  * RBD_DRV_NAME above, and # is a unique integer identifier.
@@ -173,6 +175,8 @@ struct rbd_device {
         spinlock_t              lock;           /* queue lock */
 
         struct rbd_image_header header;
+        char                    *image_id;
+        size_t                  image_id_len;
         char                    *image_name;
         size_t                  image_name_len;
         char                    *header_name;
@@ -1987,6 +1991,14 @@ static ssize_t rbd_name_show(struct device *dev,
         return sprintf(buf, "%s\n", rbd_dev->image_name);
 }
 
+static ssize_t rbd_image_id_show(struct device *dev,
+                             struct device_attribute *attr, char *buf)
+{
+        struct rbd_device *rbd_dev = dev_to_rbd_dev(dev);
+
+        return sprintf(buf, "%s\n", rbd_dev->image_id);
+}
+
 static ssize_t rbd_snap_show(struct device *dev,
                              struct device_attribute *attr,
                              char *buf)
@@ -2015,6 +2027,7 @@ static DEVICE_ATTR(client_id, S_IRUGO, rbd_client_id_show, NULL);
 static DEVICE_ATTR(pool, S_IRUGO, rbd_pool_show, NULL);
 static DEVICE_ATTR(pool_id, S_IRUGO, rbd_pool_id_show, NULL);
 static DEVICE_ATTR(name, S_IRUGO, rbd_name_show, NULL);
+static DEVICE_ATTR(image_id, S_IRUGO, rbd_image_id_show, NULL);
 static DEVICE_ATTR(refresh, S_IWUSR, NULL, rbd_image_refresh);
 static DEVICE_ATTR(current_snap, S_IRUGO, rbd_snap_show, NULL);
 static DEVICE_ATTR(create_snap, S_IWUSR, NULL, rbd_snap_add);
@@ -2026,6 +2039,7 @@ static struct attribute *rbd_attrs[] = {
         &dev_attr_pool.attr,
         &dev_attr_pool_id.attr,
         &dev_attr_name.attr,
+        &dev_attr_image_id.attr,
         &dev_attr_current_snap.attr,
         &dev_attr_refresh.attr,
         &dev_attr_create_snap.attr,
@@ -2553,6 +2567,75 @@ out_err:
         return err_ptr;
 }
 
+/*
+ * An rbd format 2 image has a unique identifier, distinct from the
+ * name given to it by the user.  Internally, that identifier is
+ * what's used to specify the names of objects related to the image.
+ *
+ * A special "rbd id" object is used to map an rbd image name to its
+ * id.  If that object doesn't exist, then there is no v2 rbd image
+ * with the supplied name.
+ *
+ * This function will record the given rbd_dev's image_id field if
+ * it can be determined, and in that case will return 0.  If any
+ * errors occur a negative errno will be returned and the rbd_dev's
+ * image_id field will be unchanged (and should be NULL).
+ */
+static int rbd_dev_image_id(struct rbd_device *rbd_dev)
+{
+        int ret;
+        size_t size;
+        char *object_name;
+        void *response;
+        void *p;
+
+        /*
+         * First, see if the format 2 image id file exists, and if
+         * so, get the image's persistent id from it.
+         */
+        size = sizeof (RBD_ID_PREFIX) + rbd_dev->image_name_len;
+        object_name = kmalloc(size, GFP_NOIO);
+        if (!object_name)
+                return -ENOMEM;
+        sprintf(object_name, "%s%s", RBD_ID_PREFIX, rbd_dev->image_name);
+        dout("rbd id object name is %s\n", object_name);
+
+        /* Response will be an encoded string, which includes a length */
+
+        size = sizeof (__le32) + RBD_IMAGE_ID_LEN_MAX;
+        response = kzalloc(size, GFP_NOIO);
+        if (!response) {
+                ret = -ENOMEM;
+                goto out;
+        }
+
+        ret = rbd_req_sync_exec(rbd_dev, object_name,
+                                "rbd", "get_id",
+                                NULL, 0,
+                                response, RBD_IMAGE_ID_LEN_MAX,
+                                CEPH_OSD_FLAG_READ, NULL);
+        dout("%s: rbd_req_sync_exec returned %d\n", __func__, ret);
+        if (ret < 0)
+                goto out;
+
+        p = response;
+        rbd_dev->image_id = ceph_extract_encoded_string(&p,
+                                                p + RBD_IMAGE_ID_LEN_MAX,
+                                                &rbd_dev->image_id_len,
+                                                GFP_NOIO);
+        if (IS_ERR(rbd_dev->image_id)) {
+                ret = PTR_ERR(rbd_dev->image_id);
+                rbd_dev->image_id = NULL;
+        } else {
+                dout("image_id is %s\n", rbd_dev->image_id);
+        }
+out:
+        kfree(response);
+        kfree(object_name);
+
+        return ret;
+}
+
 static ssize_t rbd_add(struct bus_type *bus,
                        const char *buf,
                        size_t count)
@@ -2600,6 +2683,21 @@ static ssize_t rbd_add(struct bus_type *bus,
                 goto err_out_client;
         rbd_dev->pool_id = rc;
 
+        rc = rbd_dev_image_id(rbd_dev);
+        if (!rc) {
+                rc = -ENOTSUPP; /* Not actually supporting format 2 yet */
+                goto err_out_client;
+        }
+
+        /* Version 1 images have no id; empty string is used */
+
+        rbd_dev->image_id = kstrdup("", GFP_KERNEL);
+        if (!rbd_dev->image_id) {
+                rc = -ENOMEM;
+                goto err_out_client;
+        }
+        rbd_dev->image_id_len = 0;
+
         /* Create the name of the header object */
 
         rbd_dev->header_name = kmalloc(rbd_dev->image_name_len
@@ -2691,6 +2789,7 @@ err_out_header:
 err_out_client:
         kfree(rbd_dev->header_name);
         rbd_put_client(rbd_dev);
+        kfree(rbd_dev->image_id);
 err_out_args:
         kfree(rbd_dev->mapping.snap_name);
         kfree(rbd_dev->image_name);
@@ -2746,6 +2845,7 @@ static void rbd_dev_release(struct device *dev)
 
         /* done with the id, and with the rbd_dev */
         kfree(rbd_dev->mapping.snap_name);
+        kfree(rbd_dev->image_id);
         kfree(rbd_dev->header_name);
         kfree(rbd_dev->pool_name);
         kfree(rbd_dev->image_name);