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Date: Mon, 19 Feb 2007 10:46:57 -0800
From: IdaRub <idarub@gmail.com>
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Subject: [Qemu-devel] loadvm on a read only image
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To: qemu-devel@nongnu.org

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