Re: [PATCH 6/7] btrfs-progs: Add test for super block recovery

[Nikolay Borisov <nborisov@suse.com>]

On  5.12.2017 13:12, Qu Wenruo wrote:
> 
> 
> On 2017年12月05日 18:04, Nikolay Borisov wrote:
>>
>>
>> On  5.12.2017 11:33, Qu Wenruo wrote:
>>>
>>>
>>> On 2017年12月05日 16:39, Nikolay Borisov wrote:
>>>> This functionality regressed some time ago and it was never caught. Seems no
>>>> one complained of that, but to be sure add a regression test to prevent future 
>>>> regressions.
>>>>
>>>> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
>>>
>>> One nitpick for the patch sequence, normally we put fix before test
>>> case, to avoid breaking bisect.
>>>
>>>> ---
>>>>  tests/fsck-tests/029-superblock-recovery/test.sh | 64 ++++++++++++++++++++++++
>>>>  1 file changed, 64 insertions(+)
>>>>  create mode 100755 tests/fsck-tests/029-superblock-recovery/test.sh
>>>>
>>>> diff --git a/tests/fsck-tests/029-superblock-recovery/test.sh b/tests/fsck-tests/029-superblock-recovery/test.sh
>>>> new file mode 100755
>>>> index 000000000000..beb78d6ccc22
>>>> --- /dev/null
>>>> +++ b/tests/fsck-tests/029-superblock-recovery/test.sh
>>>> @@ -0,0 +1,64 @@
>>>> +#!/bin/bash
>>>> +# Test that any superblock is correctly detected
>>>> +# and fixed by btrfs rescue
>>>> +
>>>> +source "$TOP/tests/common"
>>>> +
>>>> +check_prereq btrfs
>>>> +check_prereq mkfs.btrfs
>>>> +check_prereq btrfs-select-super
>>>> +
>>>> +setup_root_helper
>>>> +
>>>> +rm -f dev1
>>>> +run_check truncate -s 260G dev1
>>>> +loop=$(run_check_stdout $SUDO_HELPER losetup --find --show dev1)
>>>
>>> We have function to do it already.
>>> prepare_test_dev will use loopback device as fallback if $TEST_DEV is
>>> not specified.
>>> Tt can handle size well, and it also uses sparse file so no need to
>>> worry about disk usage.
>>
>> Then the test suite is not very consistent, since I copied this loopback
>> handling from some other test.
> 
> The same feeling when I am pointed that something can be replaced by
> wrappers in fstests.
> 
> Some of them can be cleaned up later.
> 
>>
>>>
>>>> +
>>>> +# Create the test file system.
>>>> +run_check $SUDO_HELPER "$TOP"/mkfs.btrfs -f "$loop"
>>>> +
>>>> +function check_corruption {
>>>> +	local sb_offset=$1
>>>> +	local source_sb=$2
>>>> +
>>>> +
>>>> +	# First we ensure we can mount it successfully
>>>> +	run_check $SUDO_HELPER mount $loop "$TEST_MNT"
>>>> +	run_check $SUDO_HELPER umount "$TEST_MNT"
>>>> +
>>>> +	# Now corrupt 1k of the superblock at sb_offset
>>>> +	run_check $SUDO_HELPER dd bs=1K count=1 seek=$(($sb_offset + 1)) if=/dev/zero of="$loop"
>>>> +
>>>> +	#if corrupting one of the sb copies, copy it over the initial superblock
>>>> +	if [ ! -z $source_sb ]; then
>>>> +		local shift_val=$((16 << $source_sb * 12 ))
>>>> +		run_check $SUDO_HELPER dd bs=1K count=4 seek=64 skip=$shift_val if="$loop" of="$loop"
>>>> +	fi
>>>
>>> Personally speaking, corrupt 64K (1st super) then corrupt the desired
>>> copy could make the function easier.
>>> Although we need to split the check part from this function, resulting
>>> something like:
>>>
>>> corrupt_super 64k
>>> corrupt_super 64m
>>> check_super_recover
>> I'm reluctant to change this function any more.  It has comments on all
>> logical steps and is self-contained and I'd rather keep it that way.
>>
>>>
>>>> +
>>>> +	run_mustfail "Mounted fs with corrupted superblock" \
>>>> +		$SUDO_HELPER mount $loop "$TEST_MNT"
>>>> +
>>>> +	# Now run btrfs rescue which should fix the superblock. It uses 2
>>>> +	# to signal success of recovery use mayfail to ignore that retval
>>>> +	# but still log the output of the command
>>>> +	run_mayfail $SUDO_HELPER "$TOP"/btrfs rescue super-recover -yv "$loop"
>>>> +	if [ $? != 2 ]; then
>>>> +		_fail "couldn't rescue super"
>>>> +	fi
>>>
>>> It's understandable to have return value other than 0 to distinguish
>>> health fs from repairable fs.
>>> But at least let's also put this into man page.
>>
>> Yeah, tell me about it, super recovery actually has 5 return values:
>>
>> 7985fe64e0e2 ("Btrfs-progs: add super-recover to recover bad supers")
>>
>>     There will be five kinds of return values:
>>
>>     0: all supers are valid, no need to recover
>>     1: usage or syntax error
>>     2: recover all bad superblocks successfully
>>     3: fail to recover bad superblocks
>>     4: abort to recover bad superblocks
> 
> Since we all agree that the return value is a messy,
> maybe we could just simplify it to 0 (all valid or successful recover)
> and 1 (the rest)?

I have no objection, but it's out of the scope of the current series.

> 
> Thanks,
> Qu
> 
>>
>>
>>>
>>> Thanks,
>>> Qu
>>>
>>>> +
>>>> +	run_check $SUDO_HELPER mount $loop "$TEST_MNT"
>>>> +	run_check $SUDO_HELPER umount "$TEST_MNT"
>>>> +}
>>>> +
>>>> +_log "Corrupting first superblock"
>>>> +check_corruption 64
>>>> +
>>>> +_log "Corrupting second superblock"
>>>> +check_corruption 65536 1
>>>> +
>>>> +_log "Corrupting third superblock"
>>>> +check_corruption 268435456 2
>>>> +
>>>> +# Cleanup
>>>> +run_check $SUDO_HELPER losetup -d "$loop"
>>>> +rm -f dev1
>>>>
>>>
>> --
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>