Re: [PATCH] btrfs-progs: convert, warn if converting a fs which won't mount

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2020/2/28 下午5:06, Anand Jain wrote:
>
>
> On 2/28/20 4:27 PM, Qu Wenruo wrote:
>>
>>
>> On 2020/2/28 下午4:03, Anand Jain wrote:
>>> On aarch64 with pagesize 64k, btrfs-convert of ext4 is successful,
>>> but it won't mount because we don't yet support subpage blocksize/
>>> sectorsize.
>>>
>>>   BTRFS error (device vda): sectorsize 4096 not supported yet, only
>>> support 65536
>>>
>>> So in this case during convert provide a warning and a 10s delay to
>>> terminate the command.
>>
>> This is no different than calling mkfs.btrfs -s 64k on x86 system.
>> And I see no warning from mkfs.btrfs.
>>
>> Thus I don't see the point of only introducing such warning to
>> btrfs-convert.
>>
>
> I have equal weight-age on the choices if blocksize != pagesize viz..
>   delay and warn (this patch)
>   quit (Nikolay).
>   keep it as it is without warning (Qu).
>
>  Here we are dealing with already user data. Should it be different
>  from mkfs?
>  Quit is fine, but convert tool should it be system neutral?

If we can't mount, btrfs-convert can easily do a revert without anything
touched for the original fs.

And, convert tool is not that system neutral.
It needs the source fs has a sector size that matches btrfs.

E.g. ext2 with 512/1K/2K sector size can't be supported by btrfs-convert
at all.

Thanks,
Qu

>
>  I am not sure.
>
>  David, any idea?
>
> Thanks, Anand
>
>> Thanks,
>> Qu
>>
>>>
>>> For example:
>>>
>>> WARNING: Blocksize 4096 is not equal to the pagesize 65536,
>>>           converted filesystem won't mount on this system.
>>>           The operation will start in 10 seconds. Use Ctrl-c to stop it.
>>> 10 9 8 7 6 5 4^C
>>>
>>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>>> ---
>>>   convert/main.c | 15 +++++++++++++++
>>>   1 file changed, 15 insertions(+)
>>>
>>> diff --git a/convert/main.c b/convert/main.c
>>> index a04ec7a36abf..f936ec37d30a 100644
>>> --- a/convert/main.c
>>> +++ b/convert/main.c
>>> @@ -1140,6 +1140,21 @@ static int do_convert(const char *devname, u32
>>> convert_flags, u32 nodesize,
>>>           error("block size is too small: %u < 4096", blocksize);
>>>           goto fail;
>>>       }
>>> +    if (blocksize != getpagesize()) {
>>> +        int delay = 10;
>>> +
>>> +        warning("Blocksize %u is not equal to the pagesize %u,\n\
>>> +         converted filesystem won't mount on this system.\n\
>>> +         The operation will start in %d seconds. Use Ctrl-C to stop
>>> it.",
>>> +            blocksize, getpagesize(), delay);
>>> +
>>> +        while (delay) {
>>> +            printf("%2d", delay--);
>>> +            fflush(stdout);
>>> +            sleep(1);
>>> +        }
>>> +    }
>>> +
>>>       if (btrfs_check_nodesize(nodesize, blocksize, features))
>>>           goto fail;
>>>       fd = open(devname, O_RDWR);
>>>
>>