From 3e83b65bb9a9f3a4d7f0200139bd947c940ec3ab Mon Sep 17 00:00:00 2001 From: Alex Elder Date: Tue, 23 Apr 2013 13:52:53 -0500 Subject: rbd: don't create sysfs entries for non-mapped snapshots When an rbd image gets mapped a device entry gets created for it under /sys/bus/rbd/devices//. Inside that directory there are sysfs files that contain information about the image: its size, feature bits, major device number, and so on. Additionally, if that image has any snapshots, a device entry gets created for each of those as a "child" of the mapped device. Each of these is a subdirectory of the mapped device, and each directory contains a few files with information about the snapshot (its snapshot id, size, and feature mask). There is no clear benefit to having those device entries for the snapshots. The information provided via sysfs of of little real value--and all of it is available via rbd CLI commands. If we still wanted to see the kernel's view of this information it could be done much more simply by including it in a single sysfs file for the mapped image. But there *is* a clear cost to supporting them. Every time a snapshot context changes, these entries need to be updated (deleted snapshots removed, new snapshots created). The rbd driver is notified of changes to the snapshot context via callbacks from an osd, and care must be taken to coordinate removal of snapshot data structures with the possibility of one these notifications occurring. Things would be considerably simpler if we just didn't have to maintain device entries for the snapshots. So get rid of them. The ability to map a snapshot of an rbd image will remain; the only thing lost will be the ability to query these sysfs directories for information about snapshots of mapped images. This resolves: http://tracker.ceph.com/issues/4796 Signed-off-by: Alex Elder Reviewed-by: Josh Durgin --- Documentation/ABI/testing/sysfs-bus-rbd | 20 -------------------- 1 file changed, 20 deletions(-) (limited to 'Documentation') diff --git a/Documentation/ABI/testing/sysfs-bus-rbd b/Documentation/ABI/testing/sysfs-bus-rbd index cd9213ccf3d..0a306476424 100644 --- a/Documentation/ABI/testing/sysfs-bus-rbd +++ b/Documentation/ABI/testing/sysfs-bus-rbd @@ -66,27 +66,7 @@ current_snap The current snapshot for which the device is mapped. -snap_* - - A directory per each snapshot - parent Information identifying the pool, image, and snapshot id for the parent image in a layered rbd image (format 2 only). - -Entries under /sys/bus/rbd/devices//snap_ -------------------------------------------------------------- - -snap_id - - The rados internal snapshot id assigned for this snapshot - -snap_size - - The size of the image when this snapshot was taken. - -snap_features - - A hexadecimal encoding of the feature bits for this snapshot. - -- cgit v1.2.3-70-g09d2