Re: btrfs convert problem

[Nikolay Borisov <nborisov@suse.com>]

On 14.09.2018 02:17, Qu Wenruo wrote:
> 
> 
> On 2018/9/14 上午12:37, Nikolay Borisov wrote:
>>
>>
>> On 13.09.2018 19:15, Serhat Sevki Dincer wrote:
>>>> -1 seems to be EPERM, is your device write-protected, readonly or
>>>> something like that ?
>>>
>>> I am able to use ext4 partition read/write, created a file and wrote
>>> in it, un/re mounted it, all is ok.
>>> The drive only has a microusb port and a little led light; no rw
>>> switch or anything like that..
>>>
>>
>> What might help is running btrfs convert under strace. So something like :
>>
>> sudo strace -f -o strace.log btrfs-convert /dev/sdb1 and then send the log.
>>
> strace would greatly help in this case.
> 
> My guess is something wrong happened in migrate_super_block(), which
> doesn't handle ret > 0 case well.
> In that case, it means pwrite 4K doesn't finish in one call, which looks
> pretty strange.

So Qu,

I'm not seeing any EPERM errors, though I see the following so you might
be right:

openat(AT_FDCWD, "/dev/sdb1", O_RDWR) = 5

followed by a lot of preads, the last one of which is:

pread64(5, 0x557a0abd10b0, 4096, 2732765184) = -1 EIO (Input/output
error)

This is then followed by a a lot of pwrites, the last 10 or so syscalls
are:

pwrite64(5, "\220\255\262\244\0\0\0\0\0\0"..., 16384, 91127808) = 16384

pwrite64(5, "|IO\233\0\0\0\0\0\0"..., 16384, 91144192) = 16384

pwrite64(5, "x\2501n\0\0\0\0\0\0"..., 16384, 91160576) = 16384

pwrite64(5, "\252\254l)\0\0\0\0\0\0"..., 16384, 91176960) = 16384

pwrite64(5, "P\256\331\373\0\0\0\0\0\0"..., 16384, 91193344) = 16384

pwrite64(5, "\3\230\230+\0\0\0\0\0\0"..., 4096, 83951616) = 4096

write(2, "ERROR: ", 7) = 7

write(2, "failed to "..., 37) = 37

write(2, "\n", 1) = 1

close(4) = 0

write(2, "WARNING: ", 9) = 9

write(2, "an error o"..., 104) = 104

write(2, "\n", 1) = 1

exit_group(1) = ?

but looking at migrate_super_block it's not doing that many writes -
just writing the sb at BTRFS_SUPER_INFO_OFFSET and then zeroing out
0..BTRFS_SUPER_INFO_OFFSET. Also the number of pwrites:
grep -c pwrite ~/Downloads/btrfs-issue/convert-strace.log
198

So the failure is not originating from migrate_super_block.

> 
> Thanks,
> Qu
>