Re: [PATCH V2] allow RAID5 to grow to RAID6 with a backup_file

[Nigel Croxon <ncroxon@redhat.com>]

On 5/8/20 10:50 AM, Nigel Croxon wrote:
>
> On 5/8/20 10:01 AM, Jes Sorensen wrote:
>> On 5/5/20 2:35 PM, Nigel Croxon wrote:
>>> This problem came in, as the user did not specify a full path with
>>> the backup_file option when growing an RAID5 array to RAID6.
>>> When the full path is specified, the symbolic link is created
>>> properly (/run/mdadm/backup_file-mdX). But the code did not support
>>> the symbolic link when looking for the backup_file. Added two
>>> checks for symlink.
>>>
>>> This addresses https://www.spinics.net/lists/raid/msg48910.html
>>> and numerous customer reported problems.
>>>
>>> V2:
>>> - Removed unneeded break; in both case-statements
>>> - Returned the error checking on call to lstat
>>>
>>> Signed-off-by: Nigel Croxon <ncroxon@redhat.com>
>>> ---
>>>   Grow.c | 21 +++++++++++++++++++--
>>>   1 file changed, 19 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/Grow.c b/Grow.c
>>> index 764374f..53245d7 100644
>>> --- a/Grow.c
>>> +++ b/Grow.c
>>> @@ -1135,6 +1135,15 @@ int reshape_open_backup_file(char *backup_file,
>>>       unsigned int dev;
>>>       int i;
>>>   +    if (lstat(backup_file, &stb) != -1) {
>>> +        switch (stb.st_mode & S_IFMT) {
>>> +        case S_IFLNK:
>>> +            return 1;
>>> +        default:
>>> +            break;
>>> +        }
>>> +    }
>>> +
>> Sorry for being a pita on this, but in this case you do the thing if the
>> lstat completes correctly, but what if it fails? In that case we should
>> error out rather than just continuing.
>>
>> Jes
>>
> There are two processes running in the reshape_array routine, the 
> original, where the user entered the mdadm grow parameter. And the 
> second, forked to call systemd mdadm-grow-continue@service.  It's in 
> the original call we want the code to continue rather than fail. It 
> needs to create the backup_file in the FS before the systemd thread runs.
>
> -Nigel
>
Jes,

Do you have more questions?  an alternate solution?

-Nigel