On 17.11.2016 21:14, Eric Blake wrote: > In order to test the effects of artificial geometry constraints > on operations like write zero or discard, we first need blkdebug > to manage these actions. Ideally, it would be nice to let these > operations also react to injected errors like read/write/flush, > but it is not trivial to turn bdrv_aio error injection (where > we return BlockAIOCB*) into bdrv_co (where we return int), not > to mention the fact that I don't want to conflict with Kevin's > concurrent work on refactoring away from bdrv_aio. So for now, > the operations merely have a TODO comment for adding error > injection. > > However, one thing we CAN test is the contract promised by the > block layer; namely, if a device has specified limits on > alignment or maximum size, then those limits must be obeyed (for > now, the blkdebug driver merely inherits limits from whatever it > is wrapping, but the next patch will further enhance it to allow > specific limit overrides). > > Tested by setting up an NBD server with export 'foo', then invoking: > $ ./qemu-io > qemu-io> open -o driver=blkdebug blkdebug::nbd://localhost:10809/foo > qemu-io> d 0 15M > qemu-io> w -z 0 15M > > Pre-patch, the server never sees the discard (it was silently > eaten by the block layer); post-patch it is passed across the > wire. Likewise, pre-patch the write is always passed with > NBD_WRITE (with 15M of zeroes on the wire), while post-patch > it can utilize NBD_WRITE_ZEROES (for less traffic). > > Signed-off-by: Eric Blake <ebl...@redhat.com> > --- > block/blkdebug.c | 61 > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 61 insertions(+)
I probably have to take my R-b back, since this patch breaks iotest 98. Max
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