From: Peter Rajnoha <prajnoha@redhat.com>
To: LVM general discussion and development <linux-lvm@redhat.com>
Subject: Re: [linux-lvm] Identifying useable block devices
Date: Thu, 16 Jan 2014 06:42:39 +0100 [thread overview]
Message-ID: <52D7714F.3080105@redhat.com> (raw)
In-Reply-To: <084301cf125a$d4b4a980$7e1dfc80$@acm.org>
On 01/16/2014 02:32 AM, Paul B. Henson wrote:
>> Anatoly Pugachev
>> Sent: Wednesday, January 15, 2014 12:25 PM
>>
>>> the /dev/mapper/.. devices are for internal use only.
>>
>> If so, how come most commands use it (df, mount, findmnt, etc..) and
>> not /dev/vg/vol notation?
>
> Because /dev/vg/vol is just a symlink to /dev/mapper/vg-vol, and mount
> dereferences it and uses the authoritative name when it actually mounts it.
This applies only if the symlinks/nodes are created directly with
libdevmapper - which is the old classical way. If udev is used to manage /dev
content for dm/lvm devices then the /dev/vg/vol is a symlink to /dev/dm-X
(also /dev/mapper/vg-vol is a symlink to /dev/dm-X). And dm-X is not a
stable name - it can be different across reboots and activation/deactivation
cycle (hence it's never used in scripts etc.). So you have to be very careful
when dereferencing symlinks.
As for mount, findmnt and other utilities from util-linux - they all use
one common code which can handle this situation (e.g. if you call
"findmnt /dev/vg/vol", it shows you /dev/mapper/vg-vol on output, not
the dm-X the /dev/vg/vol is referencing actually).
--
Peter
next prev parent reply other threads:[~2014-01-16 5:42 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-15 8:19 [linux-lvm] Identifying useable block devices Marius Vollmer
2014-01-15 15:49 ` Alasdair G Kergon
2014-01-15 16:17 ` Oliver Rath
2014-01-15 20:24 ` Anatoly Pugachev
2014-01-16 1:32 ` Paul B. Henson
2014-01-16 5:42 ` Peter Rajnoha [this message]
2014-01-16 21:03 ` Paul B. Henson
2014-01-17 7:54 ` Peter Rajnoha
2014-01-17 9:29 ` Karel Zak
2014-01-17 9:53 ` Peter Rajnoha
2014-01-16 6:04 ` Peter Rajnoha
2014-01-17 10:02 ` Marius Vollmer
2014-01-17 13:35 ` Marius Vollmer
2014-01-20 11:52 ` Peter Rajnoha
2014-01-20 11:49 ` Peter Rajnoha
2014-01-20 12:02 ` Peter Rajnoha
2014-01-22 9:23 ` Marius Vollmer
2014-01-23 11:42 ` Peter Rajnoha
2014-01-23 12:35 ` Marius Vollmer
2014-01-24 13:24 ` Peter Rajnoha
2014-01-24 13:29 ` Peter Rajnoha
2014-01-24 14:39 ` Marius Vollmer
2014-01-24 15:02 ` Peter Rajnoha
2014-01-27 7:37 ` Marius Vollmer
2014-01-24 14:50 ` Marius Vollmer
2014-01-24 15:08 ` Peter Rajnoha
2014-01-24 15:17 ` Zdenek Kabelac
2014-01-24 15:20 ` Peter Rajnoha
2014-01-22 9:02 ` Marius Vollmer
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