Currently each rbd device is allocated its own major number, which
leads to a hard limit of 230-250 images mapped at once. This commit
adds support for a new single-major device number allocation scheme,
which is hidden behind a new single_major boolean module parameter and
is disabled by default for backwards compatibility reasons. (Old
userspace cannot correctly unmap images mapped under single-major
scheme and would essentially just unmap a random image, if that.)
$ rbd showmapped
id pool image snap device
0 rbd b100 - /dev/rbd0
1 rbd b101 - /dev/rbd1
2 rbd b102 - /dev/rbd2
3 rbd b103 - /dev/rbd3
Old scheme (modprobe rbd):
$ ls -l /dev/rbd*
brw-rw---- 1 root disk 253, 0 Dec 10 12:24 /dev/rbd0
brw-rw---- 1 root disk 252, 0 Dec 10 12:28 /dev/rbd1
brw-rw---- 1 root disk 252, 1 Dec 10 12:28 /dev/rbd1p1
brw-rw---- 1 root disk 252, 2 Dec 10 12:28 /dev/rbd1p2
brw-rw---- 1 root disk 252, 3 Dec 10 12:28 /dev/rbd1p3
brw-rw---- 1 root disk 251, 0 Dec 10 12:28 /dev/rbd2
brw-rw---- 1 root disk 251, 1 Dec 10 12:28 /dev/rbd2p1
brw-rw---- 1 root disk 250, 0 Dec 10 12:24 /dev/rbd3
New scheme (modprobe rbd single_major=Y):
$ ls -l /dev/rbd*
brw-rw---- 1 root disk 253, 0 Dec 10 12:30 /dev/rbd0
brw-rw---- 1 root disk 253, 256 Dec 10 12:30 /dev/rbd1
brw-rw---- 1 root disk 253, 257 Dec 10 12:30 /dev/rbd1p1
brw-rw---- 1 root disk 253, 258 Dec 10 12:30 /dev/rbd1p2
brw-rw---- 1 root disk 253, 259 Dec 10 12:30 /dev/rbd1p3
brw-rw---- 1 root disk 253, 512 Dec 10 12:30 /dev/rbd2
brw-rw---- 1 root disk 253, 513 Dec 10 12:30 /dev/rbd2p1
brw-rw---- 1 root disk 253, 768 Dec 10 12:30 /dev/rbd3
(major 253 was assigned dynamically at module load time)
The new limit is 4096 images mapped at once, and it comes from the fact
that, as before, 256 minor numbers are reserved for each mapping.
(A follow-up commit changes the number of minors reserved and the way
we deal with partitions over that number.)
If single_major is set to true, two new sysfs interfaces show up:
/sys/bus/rbd/{add,remove}_single_major. These are to be used instead
of /sys/bus/rbd/{add,remove}, which are disabled for backwards
compatibility reasons outlined above.
Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Alex Elder <elder@linaro.org>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Introduce /sys/bus/rbd/devices/<id>/minor sysfs attribute for exporting
rbd whole disk minor numbers. This is a step towards single-major
device number allocation scheme, but also a good thing on its own.
Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Alex Elder <elder@linaro.org>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
When an rbd image gets mapped a device entry gets created for it
under /sys/bus/rbd/devices/<id>/. 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 <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Add support for getting the the information identifying the parent
image for rbd images that have them. The child image holds a
reference to its parent image specification structure. Create a new
entry "parent" in /sys/bus/rbd/image/N/ to report the identifying
information for the parent image, if any.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Record the features values for each rbd image and each of its
snapshots. This is really something that only becomes meaningful
for version 2 images, so this is just putting in place code
that will form common infrastructure.
It may be useful to expand the sysfs entries--and therefore the
information we maintain--for the image and for each snapshot.
But I'm going to hold off doing that until we start making
active use of the feature bits.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Josh proposed the following change, and I don't think I could
explain it any better than he did:
From: Josh Durgin <josh.durgin@inktank.com>
Date: Tue, 24 Jul 2012 14:22:11 -0700
To: ceph-devel <ceph-devel@vger.kernel.org>
Message-ID: <500F1203.9050605@inktank.com>
Right now the kernel still has one piece of rbd management
duplicated from the rbd command line tool: snapshot creation.
There's nothing special about snapshot creation that makes it
advantageous to do from the kernel, so I'd like to remove the
create_snap sysfs interface. That is,
/sys/bus/rbd/devices/<id>/create_snap
would be removed.
Does anyone rely on the sysfs interface for creating rbd
snapshots? If so, how hard would it be to replace with:
rbd snap create pool/image@snap
Is there any benefit to the sysfs interface that I'm missing?
Josh
This patch implements this proposal, removing the code that
implements the "snap_create" sysfs interface for rbd images.
As a result, quite a lot of other supporting code goes away.
Suggested-by: Josh Durgin <josh.durgin@inktank.com>
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
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>
Add an entry under /sys/bus/rbd/devices/<N>/ named "pool_id" that
provides the id for the pool the rbd image is assocatied with. This
is in addition to the pool name already provided.
Rename the "poolid" field in struct rbd_device to be "pool_id".
Update the documentation to reflect the addition of this new entry.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Each attribute is prefixed with "snap_".
Signed-off-by: Josh Durgin <josh.durgin@dreamhost.com>
Reviewed-by: Alex Elder <elder@dreamhost.com>
Reviewed-by: Yehuda Sadeh <yehuda@hq.newdream.net>
This doesn't interact with resizing well, since it doesn't set the
size of the device to the size at the snapshot. It's also an expensive
operation to be synchronous. Rollback can still be done with the
userspace rbd tool.
Signed-off-by: Josh Durgin <josh.durgin@dreamhost.com>
The new interface creates directories per mapped image
and under each it creates a subdir per available snapshot.
This allows keeping a cleaner interface within the sysfs
guidelines. The ABI documentation was updated too.
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Yehuda Sadeh <yehuda@hq.newdream.net>
Signed-off-by: Sage Weil <sage@newdream.net>
