Hi,
It looks like nbd driver doesn't have support
for reopen, which doesn't allow to commit qcow2 snapshots
which have nbd export as a base file.
This is because the base is opened read-only, and only
when commit job starts it reopens the base read-write.

Now after talking with Eric Blake, I understood that
nbd doesn't have the ability to tell the server to open read/only
and then change this on the fly, thus even when opening
an export as read-only the server will still allow writes.

This means that an empty .bdrv_reopen_prepare
(well except checking that export is not read-only) is supposed
to be enough.

Sending this as RFC, since I am not sure that this is the correct
solution.

Best regards,
	Maxim Levitsky

Maxim Levitsky (1):
  nbd: add empty .bdrv_reopen_prepare

 block/nbd.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

-- 
2.17.2

Patchew URL: https://patchew.org/QEMU/20190930213820.29777-1-mlevitsk@redhat.com/



Hi,

This series failed the asan build test. Please find the testing commands and
their output below. If you have Docker installed, you can probably reproduce it
locally.

=== TEST SCRIPT BEGIN ===
#!/bin/bash
export ARCH=x86_64
make docker-image-fedora V=1 NETWORK=1
time make docker-test-debug@fedora TARGET_LIST=x86_64-softmmu J=14 NETWORK=1
=== TEST SCRIPT END ===




The full log is available at
http://patchew.org/logs/20190930213820.29777-1-mlevitsk@redhat.com/testing.asan/?type=message.
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