Both bdrv_can_snapshot() and bdrv_has_snapshot() does not work as advertized.
First issue: Their names implies different porpouses, but they do the same thing
and have exactly the same code. Maybe copied and pasted and forgotten?
bdrv_has_snapshot() is called in various places for actually checking if there
is snapshots or not.
Second issue: the way bdrv_can_snapshot() verifies if a block driver supports or
not snapshots does not catch all cases. E.g.: a raw image.
So when do_savevm() is called, first thing it does is to set a global
BlockDriverState to save the VM memory state calling get_bs_snapshots().
static BlockDriverState *get_bs_snapshots(void)
{
BlockDriverState *bs;
DriveInfo *dinfo;
if (bs_snapshots)
return bs_snapshots;
QTAILQ_FOREACH(dinfo, &drives, next) {
bs = dinfo->bdrv;
if (bdrv_can_snapshot(bs))
goto ok;
}
return NULL;
ok:
bs_snapshots = bs;
return bs;
}
bdrv_can_snapshot() may return a BlockDriverState that does not support
snapshots and do_savevm() goes on.
Later on in do_savevm(), we find:
QTAILQ_FOREACH(dinfo, &drives, next) {
bs1 = dinfo->bdrv;
if (bdrv_has_snapshot(bs1)) {
/* Write VM state size only to the image that contains the state */
sn->vm_state_size = (bs == bs1 ? vm_state_size : 0);
ret = bdrv_snapshot_create(bs1, sn);
if (ret < 0) {
monitor_printf(mon, "Error while creating snapshot on '%s'\n",
bdrv_get_device_name(bs1));
}
}
}
bdrv_has_snapshot(bs1) is not checking if the device does support or has
snapshots as explained above. Only in bdrv_snapshot_create() the device is
actually checked for snapshot support.
So, in cases where the first device supports snapshots, and the second does not,
the snapshot on the first will happen anyways. I believe this is not a good
behavior. It should be an all or nothing process.
This patch addresses these issues by making bdrv_can_snapshot() actually do
what it must do and enforces better tests to avoid errors in the middle of
do_savevm(). bdrv_has_snapshot() is removed and replaced by bdrv_can_snapshot()
where appropriate.
bdrv_can_snapshot() was moved from savevm.c to block.c. It makes more sense to
me.
The loadvm_state() function was updated too to enforce that when loading a VM at
least all writable devices must support snapshots too.
Signed-off-by: Miguel Di Ciurcio Filho <miguel.fi...@gmail.com>
---
block.c | 11 +++++++++++
block.h | 1 +
savevm.c | 58 ++++++++++++++++++++++++++++++++++++----------------------
3 files changed, 48 insertions(+), 22 deletions(-)
diff --git a/block.c b/block.c
index cd70730..ace3cdb 100644
--- a/block.c
+++ b/block.c
@@ -1720,6 +1720,17 @@ void bdrv_debug_event(BlockDriverState *bs,
BlkDebugEvent event)
/**************************************************************/
/* handling of snapshots */
+int bdrv_can_snapshot(BlockDriverState *bs)
+{
+ BlockDriver *drv = bs->drv;
+ if (!drv || !drv->bdrv_snapshot_create || bdrv_is_removable(bs) ||
+ bdrv_is_read_only(bs)) {
+ return 0;
+ }
+
+ return 1;
+}
+
int bdrv_snapshot_create(BlockDriverState *bs,
QEMUSnapshotInfo *sn_info)
{
diff --git a/block.h b/block.h
index 24efeb6..fbcd8af 100644
--- a/block.h
+++ b/block.h
@@ -173,6 +173,7 @@ int bdrv_get_info(BlockDriverState *bs, BlockDriverInfo
*bdi);
const char *bdrv_get_encrypted_filename(BlockDriverState *bs);
void bdrv_get_backing_filename(BlockDriverState *bs,
char *filename, int filename_size);
+int bdrv_can_snapshot(BlockDriverState *bs);
int bdrv_snapshot_create(BlockDriverState *bs,
QEMUSnapshotInfo *sn_info);
int bdrv_snapshot_goto(BlockDriverState *bs,
diff --git a/savevm.c b/savevm.c
index dc20390..32a79d4 100644
--- a/savevm.c
+++ b/savevm.c
@@ -1574,22 +1574,6 @@ out:
return ret;
}
-/* device can contain snapshots */
-static int bdrv_can_snapshot(BlockDriverState *bs)
-{
- return (bs &&
- !bdrv_is_removable(bs) &&
- !bdrv_is_read_only(bs));
-}
-
-/* device must be snapshots in order to have a reliable snapshot */
-static int bdrv_has_snapshot(BlockDriverState *bs)
-{
- return (bs &&
- !bdrv_is_removable(bs) &&
- !bdrv_is_read_only(bs));
-}
-
static BlockDriverState *get_bs_snapshots(void)
{
BlockDriverState *bs;
@@ -1599,8 +1583,9 @@ static BlockDriverState *get_bs_snapshots(void)
return bs_snapshots;
QTAILQ_FOREACH(dinfo, &drives, next) {
bs = dinfo->bdrv;
- if (bdrv_can_snapshot(bs))
+ if (bdrv_can_snapshot(bs)) {
goto ok;
+ }
}
return NULL;
ok:
@@ -1674,12 +1659,26 @@ void do_savevm(Monitor *mon, const QDict *qdict)
#endif
const char *name = qdict_get_try_str(qdict, "name");
+ /* Verify if there is a device that doesn't support snapshots and is
writable */
+ QTAILQ_FOREACH(dinfo, &drives, next) {
+ bs = dinfo->bdrv;
+
+ if (bdrv_is_removable(bs) || bdrv_is_read_only(bs)) {
+ continue;
+ }
+
+ if (!bdrv_can_snapshot(bs)) {
+ monitor_printf(mon, "Device '%s' is writable but does not support
snapshots.\n",
+ bdrv_get_device_name(bs));
+ return;
+ }
+ }
+
bs = get_bs_snapshots();
if (!bs) {
monitor_printf(mon, "No block device can accept snapshots\n");
return;
}
-
/* ??? Should this occur after vm_stop? */
qemu_aio_flush();
@@ -1732,7 +1731,7 @@ void do_savevm(Monitor *mon, const QDict *qdict)
QTAILQ_FOREACH(dinfo, &drives, next) {
bs1 = dinfo->bdrv;
- if (bdrv_has_snapshot(bs1)) {
+ if (bdrv_can_snapshot(bs1)) {
/* Write VM state size only to the image that contains the state */
sn->vm_state_size = (bs == bs1 ? vm_state_size : 0);
ret = bdrv_snapshot_create(bs1, sn);
@@ -1756,6 +1755,21 @@ int load_vmstate(const char *name)
QEMUFile *f;
int ret;
+ /* Verify if there is a device that doesn't support snapshots and is
writable */
+ QTAILQ_FOREACH(dinfo, &drives, next) {
+ bs = dinfo->bdrv;
+
+ if (bdrv_is_removable(bs) || bdrv_is_read_only(bs)) {
+ continue;
+ }
+
+ if (!bdrv_can_snapshot(bs)) {
+ error_report("Device '%s' is writable but does not support
snapshots.",
+ bdrv_get_device_name(bs));
+ return -ENOTSUP;
+ }
+ }
+
bs = get_bs_snapshots();
if (!bs) {
error_report("No block device supports snapshots");
@@ -1767,7 +1781,7 @@ int load_vmstate(const char *name)
QTAILQ_FOREACH(dinfo, &drives, next) {
bs1 = dinfo->bdrv;
- if (bdrv_has_snapshot(bs1)) {
+ if (bdrv_can_snapshot(bs1)) {
ret = bdrv_snapshot_goto(bs1, name);
if (ret < 0) {
switch(ret) {
@@ -1829,7 +1843,7 @@ void do_delvm(Monitor *mon, const QDict *qdict)
QTAILQ_FOREACH(dinfo, &drives, next) {
bs1 = dinfo->bdrv;
- if (bdrv_has_snapshot(bs1)) {
+ if (bdrv_can_snapshot(bs1)) {
ret = bdrv_snapshot_delete(bs1, name);
if (ret < 0) {
if (ret == -ENOTSUP)
@@ -1860,7 +1874,7 @@ void do_info_snapshots(Monitor *mon)
monitor_printf(mon, "Snapshot devices:");
QTAILQ_FOREACH(dinfo, &drives, next) {
bs1 = dinfo->bdrv;
- if (bdrv_has_snapshot(bs1)) {
+ if (bdrv_can_snapshot(bs1)) {
if (bs == bs1)
monitor_printf(mon, " %s", bdrv_get_device_name(bs1));
}
--
1.7.1
