linux-kernel - Re: /dev/loop* devices not appearing in /dev (at least since 2.6.22-rc3*)

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Message-ID: <20070614172234.7f636307@localhost>
Date:	Thu, 14 Jun 2007 17:22:34 +0200
From:	Paolo Ornati <ornati@...twebnet.it>
To:	Matthew <jackdachef@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: /dev/loop* devices not appearing in /dev (at least since
 2.6.22-rc3*)

On Thu, 14 Jun 2007 16:10:44 +0200
Matthew <jackdachef@...il.com> wrote:

> I just tried out
> 
> modprobe loop max_loop=32
> 
> output of dmesg is:
> 
> [  457.607575] loop: the max_loop option is obsolete and will be
> removed in March 2008
> [  457.607578] loop: module loaded
> 
> but there are NO loop devices in /dev:
> 
> ls -l /dev/ | grep loop
> still shows nothing, strange ...

it's not strange, with your kernel version "max_loop" will just limit
the max number of loop devices at most.

This is what happens with the mentioned patch (-rc5 and later):

+	/*
+	 * loop module now has a feature to instantiate underlying device
+	 * structure on-demand, provided that there is an access dev node.
+	 * However, this will not work well with user space tool that doesn't
+	 * know about such "feature".  In order to not break any existing
+	 * tool, we do the following:
+	 *
+	 * (1) if max_loop is specified, create that many upfront, and this
+	 *     also becomes a hard limit.
+	 * (2) if max_loop is not specified, create 8 loop device on module
+	 *     load, user can further extend loop device by create dev node
+	 *     themselves and have kernel automatically instantiate actual
+	 *     device on-demand.
+	 */


So with this patch "max_loop=32" will create 32 loop devices... but
then it doesn't allow more of them.

Without options it creates 8 and you (or some userspace tool) can add
more dynamically.

-- 
	Paolo Ornati
	Linux 2.6.22-rc4-cfs-v16-g47932c49 on x86_64
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