Use of "device" argument in mount.

Use of "device" argument in mount.

[Jerome de Vivie]

In loopback mount, a pathname could be used for the device argument. As
for loopback mount, i wish to use the device argument to pass a pathname
to a stackable filesystem. Is it easyly doable ?

regards,

j.

Re: Use of "device" argument in mount.

[Christoph Hellwig]

On Fri, May 09, 2003 at 04:35:55PM +0200, Jerome de Vivie wrote:
> 
> In loopback mount, a pathname could be used for the device argument. As
> for loopback mount, i wish to use the device argument to pass a pathname
> to a stackable filesystem. Is it easyly doable ?

In Linux 2.4 it's not doable, in Linux 2.5 it's easily doable.

Re: Use of "device" argument in mount.

[Jerome de Vivie]

Christoph Hellwig wrote:
> 
> On Fri, May 09, 2003 at 04:35:55PM +0200, Jerome de Vivie wrote:
> >
> > In loopback mount, a pathname could be used for the device argument. As
> > for loopback mount, i wish to use the device argument to pass a pathname
> > to a stackable filesystem. Is it easyly doable ?
> 
> In Linux 2.4 it's not doable, in Linux 2.5 it's easily doable.

Yes: in 2.5 sb_get is definable so it's very easy. In 2.4, NFS is using
this device argument but i still don't understand how it works.

regards,

j.

-- 
Jérôme de Vivie
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Re: Use of "device" argument in mount.

[Christoph Hellwig]

[dropped the fist list Cc, it would be nice if you could not mix up
 public and stupid subscriber only lists the next time...]

On Fri, May 09, 2003 at 05:04:33PM +0200, Jerome de Vivie wrote:
> Yes: in 2.5 sb_get is definable so it's very easy. In 2.4, NFS is using
> this device argument but i still don't understand how it works.

NFS doesn't use the argument in either 2.4 or 2.5 :)

Re: [FiST] Use of "device" argument in mount.

[Erez Zadok]

In message <3EBBBCCB.8B4B24B7@free.fr>, Jerome de Vivie writes:
> 
> In loopback mount, a pathname could be used for the device argument. As
> for loopback mount, i wish to use the device argument to pass a pathname
> to a stackable filesystem. Is it easyly doable ?
> 
> regards,
> 
> j.

Jerome, I'm not sure what you're trying to do here.  Perhaps you can give
an example, w/ a sequence of ops.

Anyway, if you want a (fist) stackable f/s to recognize any kinds of new
options, you can add the parsing code in main.c:wrapfs_parse_options().
You'll see how we recognize special options such as "debug=N" and
"dir=/some/path".

Erez.

Re: [FiST] Use of "device" argument in mount.

[Jerome de Vivie]

Erez Zadok wrote:

> Jerome, I'm not sure what you're trying to do here.  Perhaps you can give
> an example, w/ a sequence of ops.

Instead of having this line inside /etc/fstab,

none    /fsdev/tstfs   tstfs  noauto,dir=/fsdev/subfs 0 0

I would like this line to work:

/fsdev/subfs  /fsdev/tstfs tstfs noauto  0 0


regards,

j.


-- 
Jérôme de Vivie
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Re: [FiST] Use of "device" argument in mount.

[Ion Badulescu]

On Fri, 9 May 2003, Jerome de Vivie wrote:

> In loopback mount, a pathname could be used for the device argument. As
> for loopback mount, i wish to use the device argument to pass a pathname
> to a stackable filesystem. Is it easyly doable ?

No, the kernel will not pass that pathname down to the filesystem, at
least in 2.4.x. Read the kernel sources (fs/super.c and fs/namespace.c) 
for details, notice how the dev_name parameter is not used in 
get_sb_nodev().

Ion

-- 
  It is better to keep your mouth shut and be thought a fool,
            than to open it and remove all doubt.

Re: Use of "device" argument in mount.

[Bryan Henderson]

>In loopback mount, a pathname could be used for the device argument.

You mean an invocation of the 'mount' program.  In the mount() system call,
you can't use a pathname for the device argument in a loopback mount.  In
the mount() system call for a loopback mount, the device argument is the
device number of a loop device (such as /dev/loop0).  The conventional
'mount' program does you the additional service, as a special case, of
configuring a loop device for the file you identify, then mounting that
device.

>i wish to use the device argument to pass a pathname
>to a stackable filesystem. Is it easily doable ?

To be analogous to the loopback mount, you'd have to add code to the
'mount' program to convert the device argument to the appropriate arguments
to mount() for the filesystem type in question.