Re: mdadm --detail showing annoying device

[Stephane Bunel <stephane.bunel@forumdesimages.fr>]

Mario 'BitKoenig' Holbe a écrit :
> Neil Brown <neilb@suse.de> wrote:
>> On Wednesday October 21, stephane.bunel@forumdesimages.fr wrote:
>>>         0       8        0        0      active sync   /dev/char/21:0
>>>         1       8       16        1      active sync   /dev/char/21:1
>> What is a block device doing in /dev/char ???  There should only be
>> character devices in there.
> 
> major 21 are usually SCSI generic devices (/dev/sg) and they are char...
> crw-rw----  1 root root  21, 0 Oct 10 21:48 /dev/sg0
> crw-rw----  1 root root  21, 1 Oct 10 21:48 /dev/sg1
> 
> The question is, why do they appear at mdadm --detail

   mdadm performs a physical walk to not follow symbolic links (cf nftw( 
FTW_PHYS ) in map_dev() ). But using stat() mdadm finaly follow the symbolic 
link and so returns the same type/major/minor as the targeted link.

   lstat() is identical to stat(), except that if path is a symbolic link, 
then the link itself is stat-ed, not the file that it refers to.


#ls -la /dev/char/21:0
lrwxrwxrwx 1 root root 13 2009-10-16 18:12 /dev/char/21:0 -> ../raid_disk0

Tested from Python:
 >>> import os, stat

Using stat:
 >>> mode = os.stat( '/dev/char/21:0' )[ stat.ST_MODE ]
 >>> stat.S_ISBLK( mode )
True

using lstat():
 >>> mode = os.lstat( '/dev/char/21:0' )[ stat.ST_MODE ]
 >>> stat.S_ISBLK( mode )
False



Stéphane Bunel.

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