[Qemu-devel] loadvm on a read only image

[Qemu-devel] loadvm on a read only image

[IdaRub]

I would like to be able to restore a snapshot from a disk image file
with read only permissions, for example stored on a cdrom.

QEMU checks if an image supports snapshots (bdrv_can_snapshot, etc)
and will fail if the disk is read only.  As a quick test, I patched
out these checks and QEMU will boot the snapshot, but it will hang
after a little while eating 100% cpu.  My guess would be this is some
timer to flush data back to disk, but I haven't looked into it at all.

The -snapshot option does support snapshots on read only images,
however when looking for snapshot it looks in the newly created
temporary backing file.  This is nice because you can create/delete
snapshots in a sandbox, but you can't restore a snapshot stored in the
original disk image.

Any ideas on what would be easier/better, trying to restore snapshots
in the base image with -snapshot, or trying to make QEMU support
snapshots on a read only image?

Thanks