Re: swidth with mdadm and RAID6

[Shailendra Tripathi <stripathi@agami.com>]

Steve Cousins wrote:

>>a 2.6.17 kernel.  So, with this in mind, is there a change that I
>>should try in libdisk/md.c?  Tim had suggested:
>>
>>	s/nr_disks/raid_disks/
>>
>>Would this be sufficient? Or should nr_disks be initialized as raid_disks
>>and then go into the switch clause?
>>    
>>
>
>I ended up just adding:
>
>	md.nr_disks = md.raid_disks;
>
>right be fore the switch statement and it worked fine in my situation.
>Not sure how this would work with other kernels etc. but I'll let you
>figure that out.  
>
>Thanks very much for your help.
>
>Steve
>
>  
>
Hi Steve,
             Technically speaking, you are doing the same thing. 
However, just write the function below to avoid any confusion.

int
md_get_subvol_stripe(
	char		*dfile,
	sv_type_t	type,
	int		*sunit,
	int		*swidth,
	int		*sectalign,
	struct stat64	*sb)
{
	if (mnt_is_md_subvol(sb->st_rdev)) {
		struct md_array_info	md;
		int			fd;

		/* Open device */
		fd = open(dfile, O_RDONLY);
		if (fd == -1)
			return 0;

		/* Is this thing on... */
		if (ioctl(fd, GET_ARRAY_INFO, &md)) {
			fprintf(stderr,
				_("Error getting MD array info from %s\n"),
				dfile);
			exit(1);
		}
		close(fd);

		/*
		 * Ignore levels we don't want aligned (e.g. linear)
		 * and deduct disk(s) from stripe width on RAID4/5/6
		 */
		switch (md.level) {
		case 6:
			md.raid_disks--;
			/* fallthrough */
		case 5:
		case 4:
			md.raid_disks--;
			/* fallthrough */
		case 1:
		case 0:
		case 10:
			break;
		default:
			return 0;
		}

		/* Update sizes */
		*sunit = md.chunk_size >> 9;
		*swidth = *sunit * md.raid_disks;
		*sectalign = (md.level == 4 || md.level == 5 || md.level == 6);

		return 1;
	}
	return 0;
}