Re: [PATCH] Btrfs: add regression test for running snapshot and send concurrently

[Wang Shilong <wangshilong1991@gmail.com>]

Hi Dave,

> On Mon, Feb 03, 2014 at 11:22:36PM +0800, Wang Shilong wrote:
>> From: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
>> 
>> Btrfs would fail to send if snapshot run concurrently, this test is to make
>> sure we have fixed the bug.
>> 
> Couple of comments below.
> 
>> +_scratch_mkfs > /dev/null 2>&1
>> +_scratch_mount
>> +
>> +
>> +touch $SCRATCH_MNT/foo
>> +
>> +# get file with fragments by using backwards writes.
>> +for i in `seq 10240 -1 1`; do
>> +	$XFS_IO_PROG -f -d -c "pwrite $(($i * 4096)) 4096" \
>> +	$SCRATCH_MNT/foo > /dev/null | _filter_xfs_io
> 
> Indentation.
> 
>> +done
>> +
>> +$BTRFS_UTIL_PROG subvolume snapshot -r $SCRATCH_MNT \
>> +	$SCRATCH_MNT/snap_1 >> $seqres.full 2>&1
>> +
>> +$BTRFS_UTIL_PROG send -f $SCRATCH_MNT/send_file \
>> +	$SCRATCH_MNT/snap_1 >> $seqres.full 2>&1 &
>> +
>> +pid=$!
>> +
>> +$BTRFS_UTIL_PROG subvolume snapshot -r $SCRATCH_MNT/snap_1 \
>> +	$SCRATCH_MNT/snap_2 >> $seqres.full 2>&1
>> +
>> +wait $pid || echo "Failed to send, see dmesg"
> 
> This seems kind of racy. It assumes that the send command
> doesn't complete before the wait $pid call is made. If $pid doesn't
> exist at this time because it has completed, wait will return 127
> and the test will fail….

Sorry for delay reply!

Maybe a better idea for this will be:

Opposite to previous way, we do snapshots background while at the
same time we do sending.

And btrfs-progs should output meaningful information on send failure, i will
make a tiny patch to address this issue. but to make this test more friendly, i
think we can still do something like:

btrfs send <..>  || echo "Failed to send"

What do you think of this way?  Feel free to tell me if there are better ideas^_^.

Thanks,
Wang
> Also, why would a failure to send result in meaingful information in
> dmesg? Shouldn't the userspace command output information to tell
> you why there was a failure into $seqres.full?
> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com

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