linux-kernel - Re: [PATCH v3 3/3] init: add support for root devices specified by partition UUID

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Message-ID: <AANLkTikUp_gz1FJW2meK9+Ow4bKX-8jVrvvSDVv=mYpQ@mail.gmail.com>
Date:	Thu, 5 Aug 2010 09:26:34 -0500
From:	Will Drewry <wad@...omium.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org, Kay Sievers <kay.sievers@...y.org>,
	Jens Axboe <axboe@...nel.dk>, Karel Zak <kzak@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Joe Perches <joe@...ches.com>, Jan Blunck <jblunck@...e.de>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: [PATCH v3 3/3] init: add support for root devices specified by 
	partition UUID

On Thu, Aug 5, 2010 at 5:55 AM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On 08/04/2010 08:22 PM, Will Drewry wrote:
>> @@ -642,6 +642,7 @@ void __init printk_all_partitions(void)
>>               struct hd_struct *part;
>>               char name_buf[BDEVNAME_SIZE];
>>               char devt_buf[BDEVT_SIZE];
>> +             u8 uuid[PARTITION_META_INFO_UUIDLTH * 2 + 1];
>>
>>               /*
>>                * Don't show empty devices or things that have been
>> @@ -660,10 +661,14 @@ void __init printk_all_partitions(void)
>>               while ((part = disk_part_iter_next(&piter))) {
>>                       bool is_part0 = part == &disk->part0;
>>
>> -                     printk("%s%s %10llu %s", is_part0 ? "" : "  ",
>> +                     uuid[0] = 0;
>> +                     if (part->info)
>> +                             part_unpack_uuid(part->info->uuid, uuid);
>> +
>> +                     printk("%s%s %10llu %s %s", is_part0 ? "" : "  ",
>>                              bdevt_str(part_devt(part), devt_buf),
>>                              (unsigned long long)part->nr_sects >> 1,
>> -                            disk_name(disk, part->partno, name_buf));
>> +                            disk_name(disk, part->partno, name_buf), uuid);
>
> Hmmm... I'm a bit worried about this.  This might break userspace
> tools.  I think it would be better to export it via sysfs.

Cool - I'm happy to drop that part from the patch.  I was more
following the spirit of the comment around making it easy for a user
to figure out what went wrong (e.g., wrong uuid) if they don't have a
root, but if there are tools parsing that output, I'd rather not break
them!

Would sysfs make sense as part of this patch series or would it be
fair game for a follow-on?  I'm inclined to wait since the UUIDs can't
be changed (blkpg support isn't wired up) except with rescans, and a
userspace tool can just walk the partition table to get the uuids.

Thanks!
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