linux-kernel - Re: tmpfs disabled in .config but in /proc/filesystems

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Date:	Sat, 6 Oct 2007 22:24:55 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...putergmbh.de>
To:	Hugh Dickins <hugh@...itas.com>
cc:	Guennadi Liakhovetski <lg@...x.de>, linux-kernel@...r.kernel.org
Subject: Re: tmpfs disabled in .config but in /proc/filesystems


On Oct 5 2007 21:49, Hugh Dickins wrote:
>> > > $ zcat /proc/config.gz | grep TMPFS
>> > > # CONFIG_TMPFS is not set
>> > > $ grep tmpfs /proc/filesystems
>> > > nodev   tmpfs
>> > 
>> > tmpfs (mm/shmem.c) is used by the kernel to support shared memory
>> > of various kinds even when CONFIG_TMPFS is not set.  But only when
>> > CONFIG_TMPFS=y can users mount a tmpfs as a fully capable filesystem.
>> > Confusing, yes: sorry for putting the fear of craziness upon you.
>> 
>> Oops, sorry, now I remember reading about this... As a matter of fact, the 
>> presence in /proc/filesystem - was it a deliberate decision, or 
>> technically preferrable or a mistake?
>
>d) None of the above!
>
>I've never really thought about it, but I think it's simply a natural
>side-effect of the register_filesystem and vfs_kern_mount it has to
>do in order to get the services it needs from the VFS.

Well you could add a new flag to the file_system_type struct
("FS_INVISIBLE") that is set when this or that condition (like TMPFS=n)
is in effect. It would be just cosmetic though.

You can't mount a lot of other filesystems like the hidden bdev,
pipefs or sockfs (it would really be nice to explore them with ls!),
yet they are not invisible either right now.

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