Am 05.10.21 um 10:36 schrieb Ilya Dryomov:
On Tue, Oct 5, 2021 at 10:19 AM Peter Lieven <p...@kamp.de> wrote:
Am 05.10.21 um 09:54 schrieb Ilya Dryomov:
On Thu, Sep 16, 2021 at 2:21 PM Peter Lieven <p...@kamp.de> wrote:
the qemu rbd driver currently lacks support for bdrv_co_block_status.
This results mainly in incorrect progress during block operations (e.g.
qemu-img convert with an rbd image as source).
This patch utilizes the rbd_diff_iterate2 call from librbd to detect
allocated and unallocated (all zero areas).
To avoid querying the ceph OSDs for the answer this is only done if
the image has the fast-diff feature which depends on the object-map and
exclusive-lock features. In this case it is guaranteed that the information
is present in memory in the librbd client and thus very fast.
If fast-diff is not available all areas are reported to be allocated
which is the current behaviour if bdrv_co_block_status is not implemented.
Signed-off-by: Peter Lieven <p...@kamp.de>
---
V2->V3:
- check rbd_flags every time (they can change during runtime) [Ilya]
- also check for fast-diff invalid flag [Ilya]
- *map and *file cant be NULL [Ilya]
- set ret = BDRV_BLOCK_ZERO | BDRV_BLOCK_OFFSET_VALID in case of an
unallocated area [Ilya]
- typo: catched -> caught [Ilya]
- changed wording about fast-diff, object-map and exclusive lock in
commit msg [Ilya]
V1->V2:
- add commit comment [Stefano]
- use failed_post_open [Stefano]
- remove redundant assert [Stefano]
- add macro+comment for the magic -9000 value [Stefano]
- always set *file if its non NULL [Stefano]
block/rbd.c | 126 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 126 insertions(+)
diff --git a/block/rbd.c b/block/rbd.c
index dcf82b15b8..3cb24f9981 100644
--- a/block/rbd.c
+++ b/block/rbd.c
@@ -1259,6 +1259,131 @@ static ImageInfoSpecific
*qemu_rbd_get_specific_info(BlockDriverState *bs,
return spec_info;
}
+typedef struct rbd_diff_req {
+ uint64_t offs;
+ uint64_t bytes;
+ int exists;
Hi Peter,
Nit: make exists a bool. The one in the callback has to be an int
because of the callback signature but let's not spread that.
+} rbd_diff_req;
+
+/*
+ * rbd_diff_iterate2 allows to interrupt the exection by returning a negative
+ * value in the callback routine. Choose a value that does not conflict with
+ * an existing exitcode and return it if we want to prematurely stop the
+ * execution because we detected a change in the allocation status.
+ */
+#define QEMU_RBD_EXIT_DIFF_ITERATE2 -9000
+
+static int qemu_rbd_co_block_status_cb(uint64_t offs, size_t len,
+ int exists, void *opaque)
+{
+ struct rbd_diff_req *req = opaque;
+
+ assert(req->offs + req->bytes <= offs);
+
+ if (req->exists && offs > req->offs + req->bytes) {
+ /*
+ * we started in an allocated area and jumped over an unallocated area,
+ * req->bytes contains the length of the allocated area before the
+ * unallocated area. stop further processing.
+ */
+ return QEMU_RBD_EXIT_DIFF_ITERATE2;
+ }
+ if (req->exists && !exists) {
+ /*
+ * we started in an allocated area and reached a hole. req->bytes
+ * contains the length of the allocated area before the hole.
+ * stop further processing.
+ */
+ return QEMU_RBD_EXIT_DIFF_ITERATE2;
Do you have a test case for when this branch is taken?
That would happen if you diff from a snapshot, the question is if it can also
happen if the image is a clone from a snapshot?
+ }
+ if (!req->exists && exists && offs > req->offs) {
+ /*
+ * we started in an unallocated area and hit the first allocated
+ * block. req->bytes must be set to the length of the unallocated area
+ * before the allocated area. stop further processing.
+ */
+ req->bytes = offs - req->offs;
+ return QEMU_RBD_EXIT_DIFF_ITERATE2;
+ }
+
+ /*
+ * assert that we caught all cases above and allocation state has not
+ * changed during callbacks.
+ */
+ assert(exists == req->exists || !req->bytes);
+ req->exists = exists;
+
+ /*
+ * assert that we either return an unallocated block or have got callbacks
+ * for all allocated blocks present.
+ */
+ assert(!req->exists || offs == req->offs + req->bytes);
+ req->bytes = offs + len - req->offs;
+
+ return 0;
+}
+
+static int coroutine_fn qemu_rbd_co_block_status(BlockDriverState *bs,
+ bool want_zero, int64_t
offset,
+ int64_t bytes, int64_t *pnum,
+ int64_t *map,
+ BlockDriverState **file)
+{
+ BDRVRBDState *s = bs->opaque;
+ int ret, r;
Nit: I would rename ret to status or something like that to make
it clear(er) that it is an actual value and never an error. Or,
even better, drop it entirely and return one of the two bitmasks
directly.
+ struct rbd_diff_req req = { .offs = offset };
+ uint64_t features, flags;
+
+ assert(offset + bytes <= s->image_size);
+
+ /* default to all sectors allocated */
+ ret = BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID;
+ *map = offset;
+ *file = bs;
+ *pnum = bytes;
+
+ /* check if RBD image supports fast-diff */
+ r = rbd_get_features(s->image, &features);
+ if (r < 0) {
+ goto out;
+ }
+ if (!(features & RBD_FEATURE_FAST_DIFF)) {
+ goto out;
+ }
+
+ /* check if RBD fast-diff result is valid */
+ r = rbd_get_flags(s->image, &flags);
+ if (r < 0) {
+ goto out;
+ }
+ if (flags & RBD_FLAG_FAST_DIFF_INVALID) {
+ goto out;
Nit: I'm not a fan of labels that cover just the return statement.
Feel free to ignore this one but I would get rid of it and replace
these gotos with returns.
That would be return with the bitmask directly coded in if I also
drop the ret variable. I can change that, no problem.
+ }
+
+ r = rbd_diff_iterate2(s->image, NULL, offset, bytes, true, true,
+ qemu_rbd_co_block_status_cb, &req);
+ if (r < 0 && r != QEMU_RBD_EXIT_DIFF_ITERATE2) {
+ goto out;
+ }
+ assert(req.bytes <= bytes);
+ if (!req.exists) {
+ if (r == 0 && !req.bytes) {
+ /*
+ * rbd_diff_iterate2 does not invoke callbacks for unallocated
areas
+ * except for the case where an overlay has a hole where the parent
+ * has not. This here catches the case where no callback was
+ * invoked at all.
+ */
The above is true in the case of diffing against a snapshot, i.e. when
the "from" snapshot has some data where the "to" revision (whether HEAD
or another snapshot) has a hole. I don't think it is true for child vs
parent (but it has been a while since I looked at the diff code). As
long as NULL is passed for fromsnapname, I would expect the callback to
be invoked only for allocated areas. If I'm right, we could simplify
qemu_rbd_co_block_status_cb() considerably.
See my comment in the callback. Can you look at the diff code or give
me at least a pointer where I can find it. I am not that familiar with
the librbd code yet.
I assumed that you added !exists handling because it came up in your
testing. If you don't have a test case then let's proceed under the
assumption that it doesn't happen for clones.
Hi Ilya,
it seems that our assumption was false. I have an image which shows holes
without diffing against
a snapshot. Do you have an idea why?
$ rbd --conf /etc/ceph/ceph-dev01.conf --id lieven info
dhp-standard/c4ca7ee9-36ce-4fc9-9d3b-ece8a4f8b83e/c1ad11d0-4f6a-4cc1-8aa3-ff3c413c1471.raw
rbd image 'c1ad11d0-4f6a-4cc1-8aa3-ff3c413c1471.raw':
size 20 GiB in 20000 objects
order 20 (1 MiB objects)
snapshot_count: 2
id: 3d6daa102e4d9f
block_name_prefix: rbd_data.3d6daa102e4d9f
format: 2
features: layering, exclusive-lock, object-map, fast-diff, deep-flatten
op_features:
flags:
create_timestamp: Tue Sep 21 14:16:56 2021
access_timestamp: Thu Jan 6 15:24:46 2022
modify_timestamp: Thu Jan 6 15:45:42 2022
$ rbd --conf /etc/ceph/ceph-dev01.conf --id lieven snap ls
dhp-standard/c4ca7ee9-36ce-4fc9-9d3b-ece8a4f8b83e/c1ad11d0-4f6a-4cc1-8aa3-ff3c413c1471.raw
SNAPID NAME SIZE PROTECTED TIMESTAMP
12297 dlp-20210921-144509 20 GiB Tue Sep 21 14:45:09 2021
17745 dlp-20220106-040000 20 GiB Thu Jan 6 04:00:01 2022
$ rbd --conf /etc/ceph/ceph-dev01.conf --id lieven diff --whole-object
dhp-standard/c4ca7ee9-36ce-4fc9-9d3b-ece8a4f8b83e/c1ad11d0-4f6a-4cc1-8aa3-ff3c413c1471.raw
| grep zero
204472320 1048576 zero
1114636288 1048576 zero
1115684864 1048576 zero
1116733440 1048576 zero
1117782016 1048576 zero
1218445312 1048576 zero
1219493888 1048576 zero
1220542464 1048576 zero
....
Best,
Peter
