Can udev match on metadata from the partition table map itself?

Can udev match on metadata from the partition table map itself?

[James Cheng]

Hi,

I have system using the Apple Partition Map partition table, instead of the DOS-style Master Boot Record partition table format. The Apple Partition Map table has some metadata for each partition, regardless of the partition type. One of those pieces of metadata is the "partition name".

I have an ext2 filesystem  on one of the partitions. Ext2 itself has the concept of filesystem names.

I want to have a rule that matches against the name in the Apple Partition Map, rather than one that matches against the ext2 filesystem name.

Is there any easy way to do this? I can think of some ugly hack, by running a PROGRAM to set some variables with the name from the partition map, and then matching against those. Any ideas for alternatives?

 -James

Re: Can udev match on metadata from the partition table map itself?

[Bryan Kadzban]

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James Cheng wrote:
> I want to have a rule that matches against the name in the Apple 
> Partition Map, rather than one that matches against the ext2 
> filesystem name.
> 
> Is there any easy way to do this? I can think of some ugly hack, by 
> running a PROGRAM to set some variables with the name from the 
> partition map, and then matching against those. Any ideas for 
> alternatives?

That "ugly hack" is actually exactly what udev does to find the ext2
filesystem label.  (Though it doesn't use PROGRAM, it uses IMPORT.  But
either way.)  It runs /lib/udev/vol_id in older versions of udev, and
/sbin/blkid (from util-linux-ng >= 2.15) in udev >= 142 or 143 or some
version around there.  This program reads the ext2 label from the FS
metadata, and prints it out (along with lots of other values, like the
filesystem's UUID).

See /lib/udev/rules.d/60-persistent-storage.rules for the rule used to
call the program in question.

If the kernel driver for the partition map exposes this name in sysfs
somewhere, then you can probably use that value instead -- but I think
that's unlikely...


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Re: Can udev match on metadata from the partition table map itself?

[David Zeuthen]

On Fri, 2009-08-07 at 14:35 -0700, James Cheng wrote:
> Hi,
> 
> I have system using the Apple Partition Map partition table, instead of the
> DOS-style Master Boot Record partition table format. The Apple Partition Map
> table has some metadata for each partition, regardless of the partition type.
> One of those pieces of metadata is the "partition name".
> 
> I have an ext2 filesystem  on one of the partitions. Ext2 itself has the
> concept of filesystem names.
> 
> I want to have a rule that matches against the name in the Apple Partition Map,
> rather than one that matches against the ext2 filesystem name.
> 
> Is there any easy way to do this? I can think of some ugly hack, by running a
> PROGRAM to set some variables with the name from the partition map, and then
> matching against those. Any ideas for alternatives?

DeviceKit-disks ships with a prober to do this since it is needed for
most disk utility programs. The prober currently supports Apple
Partition Map, Master Boot Record and GUID Partition Tables, see [1] for
output. It's GPL and the source is here

http://cgit.freedesktop.org/DeviceKit/DeviceKit-disks/tree/src/part-id.c

For performance reasons this program specifically avoids using libparted
for probing - this is because libparted likes to open all your block
devices and that kind of behavior is never ever going to work if you
want to run the program from an udev rule.

Anyway, I believe the long term plan is to teach libblkid about probing
for partition tables... that's why I never got to clean up the rather
ugly code that currently does this.

Hope this helps.

     David

[1] : # for i in /dev/sd[abc]* ; do echo "----- Device $i:"; (udevadm
info -q all -n $i |grep DKD_PARTITION); echo ""; done

----- Device /dev/sda:
E: DKD_PARTITION_TABLE=1
E: DKD_PARTITION_TABLE_SCHEME=mbr

----- Device /dev/sda1:
E: DKD_PARTITION=1
E: DKD_PARTITION_SCHEME=mbr
E: DKD_PARTITION_NUMBER=1
E: DKD_PARTITION_TYPE=0x83
E: DKD_PARTITION_SIZE2218389504
E: DKD_PARTITION_FLAGS=boot

----- Device /dev/sdb:
E: DKD_PARTITION_TABLE=1
E: DKD_PARTITION_TABLE_SCHEME=gpt

----- Device /dev/sdb1:
E: DKD_PARTITION=1
E: DKD_PARTITION_SCHEME=gpt
E: DKD_PARTITION_NUMBER=1
E: DKD_PARTITION_TYPEÎD0A0A2-B9E5-4433-87C0-68B6B72699C7
E: DKD_PARTITION_SIZE\x199982592
E: DKD_PARTITION_LABEL=A Partition Label
E: DKD_PARTITION_UUID202CF41-E9D1-47D8-A841-CBBA8A707B2C

----- Device /dev/sdc:
E: DKD_PARTITION_TABLE=1
E: DKD_PARTITION_TABLE_SCHEME=apm

----- Device /dev/sdc1:
E: DKD_PARTITION=1
E: DKD_PARTITION_SCHEME=apm
E: DKD_PARTITION_NUMBER=1
E: DKD_PARTITION_TYPE=Apple_partition_map
E: DKD_PARTITION_SIZE2256
E: DKD_PARTITION_LABEL=Apple

----- Device /dev/sdc2:
E: DKD_PARTITION=1
E: DKD_PARTITION_SCHEME=apm
E: DKD_PARTITION_NUMBER=2
E: DKD_PARTITION_TYPE=Apple_UNIX_SVR2
E: DKD_PARTITION_SIZEñ7680
E: DKD_PARTITION_LABEL=PartitionLabel
E: DKD_PARTITION_FLAGS=allocated allow_read allow_write


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Re: Can udev match on metadata from the partition table map itself?

[Kay Sievers]

On Sat, Aug 8, 2009 at 22:07, David Zeuthen<david@fubar.dk> wrote:
> Anyway, I believe the long term plan is to teach libblkid about probing
> for partition tables... that's why I never got to clean up the rather
> ugly code that currently does this.

I think Karel is working on it:
  http://git.kernel.org/?p=utils/util-linux-ng/util-linux-ng.git;a=commit;h¹46282a5fc0621c95bd3e0c19e4f72359bd731d

It really belongs into blkid, and as soon as it is available, udev
will provide this information with the default installation.

Thanks,
Kay

RE: Can udev match on metadata from the partition table map itself?

[James Cheng]

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These are just what I needed, thanks! I'll look into DeviceKit-disks, since it looks like blkid isn't ready yet. I'll have to see what the build requirements are for DeviceKit-disks, to see whether I want to import it into my build environment.

-James

-----Original Message-----
From: Kay Sievers [mailto:kay.sievers@vrfy.org] 
Sent: Saturday, August 08, 2009 1:30 PM
To: David Zeuthen
Cc: James Cheng; linux-hotplug@vger.kernel.org
Subject: Re: Can udev match on metadata from the partition table map itself?

On Sat, Aug 8, 2009 at 22:07, David Zeuthen<david@fubar.dk> wrote:
> Anyway, I believe the long term plan is to teach libblkid about probing
> for partition tables... that's why I never got to clean up the rather
> ugly code that currently does this.

I think Karel is working on it:
  http://git.kernel.org/?p=utils/util-linux-ng/util-linux-ng.git;a=commit;h¹46282a5fc0621c95bd3e0c19e4f72359bd731d

It really belongs into blkid, and as soon as it is available, udev
will provide this information with the default installation.

Thanks,
Kay
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Re: Can udev match on metadata from the partition table map itself?

[Karel Zak]

On Sat, Aug 08, 2009 at 10:29:56PM +0200, Kay Sievers wrote:
> On Sat, Aug 8, 2009 at 22:07, David Zeuthen<david@fubar.dk> wrote:
> > Anyway, I believe the long term plan is to teach libblkid about probing
> > for partition tables... that's why I never got to clean up the rather
> > ugly code that currently does this.
> 
> I think Karel is working on it:
>   http://git.kernel.org/?p=utils/util-linux-ng/util-linux-ng.git;a=commit;h¹46282a5fc0621c95bd3e0c19e4f72359bd731d
> 
> It really belongs into blkid, and as soon as it is available, udev
> will provide this information with the default installation.

 Yes. I'd like to try to export partition labels (e.g. mac partition
 name) and partition UUIDs (e.g. EFI GUID partition UUID) to mount(8),
 fsck(8), swapon(8), ... So it will be possible to indicate block
 devices independently on filesystems.

    Karel

-- 
 Karel Zak  <kzak@redhat.com>