On 2013年12月04日 14:34, Benoît Canet wrote:
Le Wednesday 04 Dec 2013 à 14:12:19 (+0800), Fam Zheng a écrit :
On 2013年12月04日 13:20, Benoît Canet wrote:
Le Wednesday 04 Dec 2013 à 11:47:22 (+0800), Fam Zheng a écrit :
On 2013年12月03日 21:26, Benoît Canet wrote:
---
block.c | 64 +++++++++++++++++++++++++++++++++++++++++------
block/blkverify.c | 2 +-
include/block/block.h | 16 +++++++++---
include/block/block_int.h | 9 ++++---
4 files changed, 75 insertions(+), 16 deletions(-)
diff --git a/block.c b/block.c
index 8016ff2..0569cb2 100644
--- a/block.c
+++ b/block.c
@@ -4945,21 +4945,69 @@ int bdrv_amend_options(BlockDriverState *bs,
QEMUOptionParameter *options)
return bs->drv->bdrv_amend_options(bs, options);
}
-ExtSnapshotPerm bdrv_check_ext_snapshot(BlockDriverState *bs)
+/* will be used to recurse on single child block filter until first format
+ * (single child block filter will store their child in bs->file)
+ */
+ExtSnapshotPerm bdrv_generic_check_ext_snapshot(BlockDriverState *bs,
+ BlockDriverState *candidate)
{
- if (bs->drv->bdrv_check_ext_snapshot) {
- return bs->drv->bdrv_check_ext_snapshot(bs);
+ if (!bs->drv) {
+ return EXT_SNAPSHOT_FORBIDDEN;
}
- if (bs->file && bs->file->drv && bs->file->drv->bdrv_check_ext_snapshot) {
- return bs->file->drv->bdrv_check_ext_snapshot(bs);
+ if (!bs->drv->authorizations[BS_CANT_SNAPSHOT]) {
This double negative feels hard to read for me.
+ if (bs == candidate) {
+ return EXT_SNAPSHOT_ALLOWED;
+ } else {
+ return EXT_SNAPSHOT_FORBIDDEN;
+ }
}
- /* external snapshots are allowed by default */
- return EXT_SNAPSHOT_ALLOWED;
+ if (!bs->drv->authorizations[BS_FILTER_PASS_DOWN]) {
+ return EXT_SNAPSHOT_FORBIDDEN;
+ }
+
+ if (!bs->file) {
+ return EXT_SNAPSHOT_FORBIDDEN;
+ }
+
+ return bdrv_recurse_check_ext_snapshot(bs->file, candidate);
}
-ExtSnapshotPerm bdrv_check_ext_snapshot_forbidden(BlockDriverState *bs)
+ExtSnapshotPerm bdrv_recurse_check_ext_snapshot(BlockDriverState *bs,
+ BlockDriverState *candidate)
{
+ if (bs->drv && bs->drv->bdrv_check_ext_snapshot) {
+ return bs->drv->bdrv_check_ext_snapshot(bs, candidate);
+ }
Maybe I'm missing something, but if a driver always returns positive
permit, despite of what candidate is (or even it's relevant to bs),
then doesn't it also affect other devices? because...
+
+ return bdrv_generic_check_ext_snapshot(bs, candidate);
+}
+
+/* This function check if the candidate bs has snapshots authorized by going
+ * down the forest of bs, skipping filters and stopping on the the first bses
+ * authorizing snapshots
+ */
+ExtSnapshotPerm bdrv_check_ext_snapshot(BlockDriverState *candidate)
+{
+ BlockDriverState *bs;
+
+ /* walk down the bs forest recursively */
+ QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
this iterates through all the known graph trees (device_list),
instead of limiting to only the device that candidate belongs to.
The recursion termination success is candidate == bs.
This make sure that the scan of the other tree of the forest will not return any
spurious success.
But the "candidate == bs" check is in
bdrv_generic_check_ext_snapshot, which gets short-circuited by
driver implementation if the driver implements it, in
bdrv_recurse_check_ext_snapshot.
So if I have an "always yes" drv->bdrv_check_ext_snapshot and it
happens to be the first one in bdrv_states, I will allow all
snapshot operations.
My bad I forgot to document the drv_>bdrv_check_ext_snapshot.
It meant to be recursive and only for twisted block filter like this one
(quorum):
static ExtSnapshotPerm quorum_check_ext_snapshot(BlockDriverState *bs,
BlockDriverState *candidate)
{
BDRVQuorumState *s = bs->opaque;
int i;
for (i = 0; i < s->total; i++) {
ExtSnapshotPerm perm = bdrv_recurse_check_ext_snapshot(s->bs[i],
candidate);
if (perm == EXT_SNAPSHOT_ALLOWED) {
return EXT_SNAPSHOT_ALLOWED;
}
}
return EXT_SNAPSHOT_FORBIDDEN;
}
Maybe the callback needs a serious rename.
OK, I see how it works. Default is forbidden and you iterate on all the
devices trying to find some BDS recognizes and returns "allow". This
positive vote is so powerful and I hope no driver will ever abuse it in
the future. :)
But I still think if "bs" doesn't "recognize candidate" (in other words,
they are irrelevant to each other), it should return a 3rd value like
"EXT_SNAPSHOT_NOTCARE", which is more intuitive.
Thanks for your explanation.
Fam
