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iotests: New test 223 for exporting dirty bitmap over NBD

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Although this test is NOT a full test of image fleecing (as it
intentionally uses just a single block device directly exported
over NBD, rather than trying to set up a blockdev-backup job with
multiple BDS involved), it DOES prove that qemu as a server is
able to properly expose a dirty bitmap over NBD.

When coupled with image fleecing, it is then possible for a
third-party client to do an incremental backup by using
qemu-img map with the x-dirty-bitmap option to learn which parts
of the file are dirty (perhaps confusingly, they are the portions
mapped as "data":false - which is part of the reason this is
still in the x- experimental namespace), along with another
normal client (perhaps 'qemu-nbd -c' to expose the server over
/dev/nbd0 and then just use normal I/O on that block device) to
read the dirty sections.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20180702191458.28741-3-eblake@redhat.com>
Tested-by: John Snow <jsnow@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
This commit is contained in:
Eric Blake 2018-07-02 14:14:58 -05:00
parent 216ee3657e
commit a1532a225a
3 changed files with 188 additions and 0 deletions
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tests/qemu-iotests/group
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@ -221,3 +221,4 @@
219 rw auto
221 rw auto quick
222 rw auto quick
223 rw auto quick