From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jan Hudec <bulb@ucw.cz>
Subject: Re: userspace buffer in read/write system call
Date: Sat, 20 May 2006 18:23:32 +0200
Message-ID: <20060520162332.GC4128@efreet.light.src>
References: <20060519140148.93081.qmail@web37211.mail.mud.yahoo.com>
Mime-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha1;
	protocol="application/pgp-signature"; boundary="bAmEntskrkuBymla"
Cc: linux-fsdevel@vger.kernel.org
Return-path: <linux-fsdevel-owner@vger.kernel.org>
Received: from cimice0.lam.cz ([212.71.168.90]:51380 "EHLO cimice.yo.cz")
	by vger.kernel.org with ESMTP id S1751421AbWETQXf (ORCPT
	<rfc822;linux-fsdevel@vger.kernel.org>);
	Sat, 20 May 2006 12:23:35 -0400
To: UZAIR LAKHANI <uzairr_bs1b@yahoo.com>
Content-Disposition: inline
In-Reply-To: <20060519140148.93081.qmail@web37211.mail.mud.yahoo.com>
Sender: linux-fsdevel-owner@vger.kernel.org
List-Id: linux-fsdevel.vger.kernel.org


--bAmEntskrkuBymla
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Fri, May 19, 2006 at 07:01:48 -0700, UZAIR LAKHANI wrote:
> Hello All,
>=20
> Suppose I want to implement read/write file operations
> of a simple file system. Consider the read system
> call. The file system's struct file_operations
> function that will be called is this
>=20
> ssize_t (*read) (struct file *, char *, size_t, loff_t
> *);
>=20
> The char * in the arguments of read is a user-space
> buffer pointer. Suppose I don't want to send this
> buffer that we have got to the generic_file_read
> function or some other function and instead want to

Particularly to generic_file_read you **DO** want to pass it --
generic_file_read takes a user-space address just like the read file
operation. In fact some filesystems assign generic_file_read directly to
their read file operation slot.

> create a new buffer and send it to the
> generic_file_read (or other) function. Then copy this

Just have a look in any other filesystem. Does it do anything like that?!?!

> buffer that we have sent to the generic_file_read to
> the actual buffer that we had received so that the
> call can be completed and the buffer received is
> filled.
>=20
> Consider what I am doing now is
>=20
> static ssize_t
> foo_read(file_t *file, char *buf, size_t count, loff_t
> *ppos)
> {
> 	...
> 	char __user local_buffer[10];	//TODO
> 	count =3D 10;			// setting a new count=09
>=20
> 	// read_XXX below is to be taken as a function that=20
> 	// will do read for us e.g. generic_file_read can be=20
> 	// such a function
> 	err =3D read_XXX( file, local_buffer, count, ppos);
>=20
> 	// now copy local_buffer into buf=20
> 	...
>=20
> 	// the err is -14 or BAD ADDRESS
> 	return err;
> }
>=20
> Any help regrading this is welcome.
>=20
> Thanks,
> Uzair Lakhani,
> Karachi, Pakistan.
>=20
>=20
> __________________________________________________
> Do You Yahoo!?
> Tired of spam?  Yahoo! Mail has the best spam protection around=20
> http://mail.yahoo.com=20
> -
> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" =
in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
--=20
						 Jan 'Bulb' Hudec <bulb@ucw.cz>

--bAmEntskrkuBymla
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: Digital signature
Content-Disposition: inline

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.3 (GNU/Linux)

iD8DBQFEb0KERel1vVwhjGURAuz+AKDbOV7BLLQC25XSZZvv+aL1m7vp6wCdHPU0
eEHFqATqjpNCo66a3S5SfWQ=
=0KOr
-----END PGP SIGNATURE-----

--bAmEntskrkuBymla--