The only caller of rbd_header_from_disk() is rbd_read_header().
It passes as allocated_snaps the number of snapshots it will
have received from the server for the snapshot context that
rbd_header_from_disk() is to interpret. The first time through
it provides 0--mainly to extract the number of snapshots from
the snapshot context header--so that it can allocate an
appropriately-sized buffer to receive the entire snapshot
context from the server in a second request.
rbd_header_from_disk() will not fill in the array of snapshot ids
unless the number in the snapshot matches the number the caller
had allocated.
This patch adjusts that logic a little further to be more efficient.
rbd_read_header() doesn't even examine the snapshot context unless
the snapshot count (stored in header->total_snaps) matches the
number of snapshots allocated. So rbd_header_from_disk() doesn't
need to allocate or fill in the snapshot context field at all in
that case.
Signed-off-by: Alex Elder <elder@xxxxxxxxxxx>
---
drivers/block/rbd.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
Index: b/drivers/block/rbd.c
===================================================================
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -541,7 +541,14 @@ static int rbd_header_from_disk(struct r
header->comp_type = ondisk->options.comp_type;
header->total_snaps = snap_count;
- /* Set up the snapshot context */
+ /*
+ * If the number of snapshot ids provided by the caller
+ * doesn't match the number in the entire context there's
+ * no point in going further. Caller will try again after
+ * getting an updated snapshot context from the server.
+ */
+ if (allocated_snaps != snap_count)
+ return 0;
size = sizeof (struct ceph_snap_context);
size += snap_count * sizeof (header->snapc->snaps[0]);
@@ -553,8 +560,10 @@ static int rbd_header_from_disk(struct r
header->snapc->seq = le64_to_cpu(ondisk->snap_seq);
header->snapc->num_snaps = snap_count;
- if (snap_count && allocated_snaps == snap_count) {
- int i;
+ /* Fill in the snapshot information */
+
+ if (snap_count) {
+ u32 i;
for (i = 0; i < snap_count; i++) {
header->snapc->snaps[i] =
--
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