rbd: get the snapshot context for a v2 image

Fetch the snapshot context for an rbd format 2 image by calling
the "get_snapcontext" method on its header object.

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

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index b8b8271..b673a8d 100644 (file)
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -62,6 +62,7 @@
 #define RBD_MINORS_PER_MAJOR   256             /* max minors per blkdev */
 
 #define RBD_MAX_SNAP_NAME_LEN  32
+#define RBD_MAX_SNAP_COUNT     510     /* allows max snapc to fit in 4KB */
 #define RBD_MAX_OPT_LEN                1024
 
 #define RBD_SNAP_HEAD_NAME     "-"
@@ -2240,6 +2241,84 @@ static int rbd_dev_v2_features(struct rbd_device *rbd_dev)
                                                &rbd_dev->header.features);
 }
 
+static int rbd_dev_v2_snap_context(struct rbd_device *rbd_dev)
+{
+       size_t size;
+       int ret;
+       void *reply_buf;
+       void *p;
+       void *end;
+       u64 seq;
+       u32 snap_count;
+       struct ceph_snap_context *snapc;
+       u32 i;
+
+       /*
+        * We'll need room for the seq value (maximum snapshot id),
+        * snapshot count, and array of that many snapshot ids.
+        * For now we have a fixed upper limit on the number we're
+        * prepared to receive.
+        */
+       size = sizeof (__le64) + sizeof (__le32) +
+                       RBD_MAX_SNAP_COUNT * sizeof (__le64);
+       reply_buf = kzalloc(size, GFP_KERNEL);
+       if (!reply_buf)
+               return -ENOMEM;
+
+       ret = rbd_req_sync_exec(rbd_dev, rbd_dev->header_name,
+                               "rbd", "get_snapcontext",
+                               NULL, 0,
+                               reply_buf, size,
+                               CEPH_OSD_FLAG_READ, NULL);
+       dout("%s: rbd_req_sync_exec returned %d\n", __func__, ret);
+       if (ret < 0)
+               goto out;
+
+       ret = -ERANGE;
+       p = reply_buf;
+       end = (char *) reply_buf + size;
+       ceph_decode_64_safe(&p, end, seq, out);
+       ceph_decode_32_safe(&p, end, snap_count, out);
+
+       /*
+        * Make sure the reported number of snapshot ids wouldn't go
+        * beyond the end of our buffer.  But before checking that,
+        * make sure the computed size of the snapshot context we
+        * allocate is representable in a size_t.
+        */
+       if (snap_count > (SIZE_MAX - sizeof (struct ceph_snap_context))
+                                / sizeof (u64)) {
+               ret = -EINVAL;
+               goto out;
+       }
+       if (!ceph_has_room(&p, end, snap_count * sizeof (__le64)))
+               goto out;
+
+       size = sizeof (struct ceph_snap_context) +
+                               snap_count * sizeof (snapc->snaps[0]);
+       snapc = kmalloc(size, GFP_KERNEL);
+       if (!snapc) {
+               ret = -ENOMEM;
+               goto out;
+       }
+
+       atomic_set(&snapc->nref, 1);
+       snapc->seq = seq;
+       snapc->num_snaps = snap_count;
+       for (i = 0; i < snap_count; i++)
+               snapc->snaps[i] = ceph_decode_64(&p);
+
+       rbd_dev->header.snapc = snapc;
+
+       dout("  snap context seq = %llu, snap_count = %u\n",
+               (unsigned long long) seq, (unsigned int) snap_count);
+
+out:
+       kfree(reply_buf);
+
+       return 0;
+}
+
 /*
  * Scan the rbd device's current snapshot list and compare it to the
  * newly-received snapshot context.  Remove any existing snapshots
@@ -2779,6 +2858,12 @@ static int rbd_dev_v2_probe(struct rbd_device *rbd_dev)
        ret = rbd_dev_v2_features(rbd_dev);
        if (ret < 0)
                goto out_err;
+
+       /* Get the snapshot context */
+
+       ret = rbd_dev_v2_snap_context(rbd_dev);
+       if (ret)
+               goto out_err;
        rbd_dev->image_format = 2;
 
        dout("discovered version 2 image, header name is %s\n",