On 19.01.24 17:46, Fiona Ebner wrote:
Am 17.01.24 um 17:07 schrieb Vladimir Sementsov-Ogievskiy:
Add a parameter that enables discard-after-copy. That is mostly useful
in "push backup with fleecing" scheme, when source is snapshot-access
format driver node, based on copy-before-write filter snapshot-access
API:
[guest] [snapshot-access] ~~ blockdev-backup ~~> [backup target]
| |
| root | file
v v
[copy-before-write]
| |
| file | target
v v
[active disk] [temp.img]
In this case discard-after-copy does two things:
- discard data in temp.img to save disk space
- avoid further copy-before-write operation in discarded area
Note that we have to declare WRITE permission on source in
copy-before-write filter, for discard to work.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@yandex-team.ru>
Unfortunately, setting BLK_PERM_WRITE unconditionally breaks
blockdev-backup for a read-only node (even when not using discard-source):
Ohh, right.
So, that's the place when we have to somehow pass through discrard-souce option
to CBW filter, so that it know that WRITE permission is needed. Will try in v3.
Thanks again for testing!
#!/bin/bash
./qemu-img create /tmp/disk.raw -f raw 1G
./qemu-img create /tmp/backup.raw -f raw 1G
./qemu-system-x86_64 --qmp stdio \
--blockdev
raw,node-name=node0,file.driver=file,file.filename=/tmp/disk.raw,read-only=true
\
--blockdev raw,node-name=node1,file.driver=file,file.filename=/tmp/backup.raw \
<<EOF
{"execute": "qmp_capabilities"}
{"execute": "blockdev-backup", "arguments": { "device": "node0", "target": "node1", "sync": "full",
"job-id": "backup0" } }
EOF
The above works before applying this patch, but leads to an error
afterwards:
{"error": {"class": "GenericError", "desc": "Block node is read-only"}}
Best Regards,
Fiona
--
Best regards,
Vladimir
