Re: [PATCH] mdadm: Deprecate the obsolete --auto-detect option

["Masalkhi, Abd Alrhman" <abd.masalkhi@gatech.edu>]

Hi Mariusz,

On Wed, Oct 28, 2026 at 10:03 +0100, Mariusz Tkaczyk wrote:
> On Thu, 15 Oct 2026 13:03:59 +0000
> "Masalkhi, Abd Alrhman" <abd.masalkhi@gatech.edu> wrote:
>
>> From: Abd-Alrhman Masalkhi <abd.masalkhi@gatech.edu>
>> 
>> --auto-detect opened md0 (9:0) and issued the RAID_AUTORUN ioctl to
>> ask the kernel to start the arrays it had auto-detected. The kernel
>> removed this ioctl in commit d82fa81c2364 ("md: replace the
>> RAID_AUTORUN ioctl with a direct function call"). Before that, it
>> worked only when md was built into the kernel. Since then, md_ioctl()
>
> Redhat still builds-in md into kernel so there is chance that someone
> is using it.
>
>
>> has rejected it with ENOTTY, making --auto-detect ineffective on
>> current kernels.
>
>
> Hello,
> Do you mind to submit github PRs for mdadm patches?
> https://github.com/md-raid-utilities/mdadm
>

Sure, I will submit the next version as a GitHub pull request.

One question, should I also send the RFC patches for updating mdadm to
use the new UAPI to the mailing list, or is submitting GitHub PRs
sufficient?

> mdadm community is the most active over the github today.
>
> Indeed, it has been removed 6 years ago. The question is if 6 years is
> enough to stop supporting the configurations with new mdadm and old
> kernel. I think it is not enough.
>
> I would do that at least 10 years after kernel part removed.
>
> What can be done here is warning and improved error message saying that
> "The option is deprecated and probably it is not supported with this
> kernel". If you wish you can be more detailed and add validation
> against kernel version but I have no hard feeling to that. It is minor
> case, probably not used because no one ever complained about the removed
> ioctl.
>
> You can left some TODO message saying that after 2030y it can
> removed- that would be helpful for future maintainers.
>

Thanks for the clarification. I will make the changes accordingly.

> Thanks,
> Mariusz
>
>> 
>> Remove autodetect(). Keep the option for now to avoid breaking
>> existing scripts, and print a warning message when it is used.
>> 
>> Signed-off-by: Abd-Alrhman Masalkhi <abd.masalkhi@gatech.edu>
>> ---
>>  Manage.c | 13 -------------
>>  mdadm.c  |  2 +-
>>  mdadm.h  |  1 -
>>  3 files changed, 1 insertion(+), 15 deletions(-)
>> 
>> diff --git a/Manage.c b/Manage.c
>> index 40d52cfc..d38336a0 100644
>> --- a/Manage.c
>> +++ b/Manage.c
>> @@ -1738,19 +1738,6 @@ abort:
>>  	return !test && busy ? 2 : 1;
>>  }
>>  
>> -int autodetect(void)
>> -{
>> -	/* Open any md device, and issue the RAID_AUTORUN ioctl */
>> -	int rv = 1;
>> -	int fd = dev_open("9:0", O_RDONLY);
>> -	if (fd >= 0) {
>> -		if (ioctl(fd, RAID_AUTORUN, 0) == 0)
>> -			rv = 0;
>> -		close_fd(&fd);
>> -	}
>> -	return rv;
>> -}
>> -
>>  int Update_subarray(char *dev, char *subarray, enum update_opt
>> update, struct mddev_ident *ident, int verbose)
>>  {
>> diff --git a/mdadm.c b/mdadm.c
>> index 2517b037..c4e234e3 100644
>> --- a/mdadm.c
>> +++ b/mdadm.c
>> @@ -1744,7 +1744,7 @@ int main(int argc, char *argv[])
>>  			rv = Incremental(devlist, &c, ss);
>>  		break;
>>  	case AUTODETECT:
>> -		autodetect();
>> +		pr_err("--auto-detect has no effect. It is
>> deprecated and will be removed in future releases.\n"); break;
>>  	}
>>  	if (ss) {
>> diff --git a/mdadm.h b/mdadm.h
>> index deac7a56..985951d3 100644
>> --- a/mdadm.h
>> +++ b/mdadm.h
>> @@ -1434,7 +1434,6 @@ extern int Manage_stop(char *devname, int fd,
>> int quiet, extern int Manage_subdevs(char *devname, int fd,
>>  			  struct mddev_dev *devlist, int verbose,
>> int test, enum update_opt update, int force);
>> -extern int autodetect(void);
>>  extern int Grow_Add_device(char *devname, int fd, char *newdev);
>>  extern int Grow_addbitmap(char *devname, int fd,
>>  			  struct context *c, struct shape *s);
>
>

-- 
Best Regards,
Abd-Alrhman