Re: [Qemu-devel] [PATCH v3 3/3] iotests: Add test for external image truncation

[Kevin Wolf <kwolf@redhat.com>]

Am 23.10.2014 um 09:26 hat Max Reitz geschrieben:
> On 2014-10-22 at 18:50, Eric Blake wrote:
> >On 10/22/2014 09:57 AM, Max Reitz wrote:
> >>It should not be happening, but it is possible to truncate an image
> >>outside of qemu while qemu is running (or any of the qemu tools using
> >>the block layer. raw_co_get_block_status() should not break then.
> >>
> >>Signed-off-by: Max Reitz <mreitz@redhat.com>
> >>---
> >>  tests/qemu-iotests/102     | 15 +++++++++++++++
> >>  tests/qemu-iotests/102.out |  9 +++++++++
> >>  2 files changed, 24 insertions(+)
> >>
> >>diff --git a/tests/qemu-iotests/102 b/tests/qemu-iotests/102
> >>index 34b363f..027198b 100755
> >>--- a/tests/qemu-iotests/102
> >>+++ b/tests/qemu-iotests/102
> >>@@ -58,6 +58,21 @@ truncate -s $((5 * 64 * 1024)) "$TEST_IMG"
> >>  $QEMU_IO -c map "$TEST_IMG"
> >>  $QEMU_IMG map "$TEST_IMG"
> >>+echo
> >>+echo '=== Testing map on an image file truncated outside of qemu ==='
> >>+echo
> >>+
> >>+# Same as above, only now we concurrently truncate and map the image
> >>+_make_test_img $IMG_SIZE
> >>+$QEMU_IO -c 'write 0 64k' "$TEST_IMG" | _filter_qemu_io
> >>+
> >>+(sleep 0.2; $QEMU_IO -c map "$TEST_IMG"; $QEMU_IMG map "$TEST_IMG") &
> >Should you use '&&' instead of ';' between the three operations, to
> >ensure that you can detect failure of the overall background subshell? [1]
> 
> No, I don't think so. The output is compared against the test output
> and I probably want to have both the output of qemu-io -c map and
> qemu-img map, even if one fails.
> 
> >Fractional sleep is a GNU extension, and won't work on BSD.  It adds .8
> >seconds to make this sleep 1, but the extra portability may be worth it.
> 
> Probably so, yes.
> 
> >It also makes the test more robust, and less likely to fail a race in a
> >heavily-loaded tester.  Then again, it is not the first use of
> >fractional sleep in the testsuite.
> >
> >Hmm - does the blkdebug driver allow us to pause qemu operation to
> >reliably allow an external action callback, and then resume qemu?  That
> >might be less prone to race failure, as well as reducing the need to
> >blindly sleep for a fixed amount of time.
> 
> It does not yet. But when you're asking like this, I'm willing to
> build a time block driver which pauses one second for every sector
> you're reading from it.
> 
> Okay, so without kidding, I think to make this right, we could try
> to keep qemu-io open, do the truncate, and then continue writing
> commands to qemu-io. I think I can do that by not using qemu-io but
> qemu directly and then use the common.qemu functions (along with HMP
> qemu-io). Of course, this makes testing qemu-img map impossible, but
> using blkdebug would have done the same, probably. Also, just
> qemu-io -c map should be enough for this case.

It should be possible to stop qemu-img at a good enough place with
blkdebug. The problem would just be how to resume...

I agree that the qemu-img test doesn't add much here anyway.

> >>+truncate -s $((5 * 64 * 1024)) "$TEST_IMG"
> >truncate is a GNU program, not necessarily available on all platforms;
> >but this is not the first test using it.
> 
> Well, if it's not the first test, I'm inclined to leave it. But
> since I'm going to respin anyway and you're asking so kindly, I'll
> reach deep into my box of tricks and use qemu-img resize "json:{'driver':'raw','file':{'driver':'file','filename':'$TEST_IMG'}}"
> $((5 * 64 * 1024)).

What's wrong with 'qemu-img resize -f raw "$TEST_IMG"'? Also doesn't
hardcode the protocol.

> Speaking of resize not taking a format, we should probably at some
> point in time add an input format parameter to all of the qemu-img
> subcommands (resize and snapshot don't have one yet).

Well, _my_ resize does have one and has been there since resize was
introduced in 2010 (commit ae6b0ed6).

Kevin