Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261177AbVEaWa5 (ORCPT ); Tue, 31 May 2005 18:30:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261182AbVEaW3o (ORCPT ); Tue, 31 May 2005 18:29:44 -0400 Received: from adsl-69-149-197-17.dsl.austtx.swbell.net ([69.149.197.17]:48285 "EHLO gw.microgate.com") by vger.kernel.org with ESMTP id S261177AbVEaW2b (ORCPT ); Tue, 31 May 2005 18:28:31 -0400 Subject: Re: [PATCH 1/2] Introduce tty_unregister_ldisc() From: Paul Fulghum To: Alexey Dobriyan Cc: Andrew Morton , linux-kernel@vger.kernel.org In-Reply-To: <200505312356.00853.adobriyan@gmail.com> References: <200505312356.00853.adobriyan@gmail.com> Content-Type: text/plain Date: Tue, 31 May 2005 17:28:11 -0500 Message-Id: <1117578491.4627.14.camel@at2.pipehead.org> Mime-Version: 1.0 X-Mailer: Evolution 2.0.4 (2.0.4-4) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4521 Lines: 115 This patch is wrong. Please do not apply. An unmodified ldisc driver (externally maintained) will continue to call tty_register_ldisc with NULL, but the new behavior will be to set the ldisc pointer to NULL but have LDISC_FLAG_DEFINED set. If you feel it is absolutely necessary to add this new function for cosmetic reasons, then leave the old behavior in place and make tty_unregister_ldisc a wrapper to tty_register_ldisc that uses a NULL pointer. This preserves sanity and compatibility. The existing function has a bug: If new_ldisc != NULL and LDISC_FLAG_DEFINED is set, the ldisc is switched to new_ldisc without checking for non-zero refcount of current ldisc. -- Paul Fulghum paulkf@microgate.com On Tue, 2005-05-31 at 23:56 +0400, Alexey Dobriyan wrote: > It's a bit strange to see tty_register_ldisc() call in modules' exit functions. > ... > --- linux-tty_register_ldisc_000/Documentation/tty.txt 2005-05-31 20:12:47.000000000 +0400 > +++ linux-tty_register_ldisc_001/Documentation/tty.txt 2005-05-31 23:19:32.000000000 +0400 > @@ -22,7 +22,7 @@ copy of the structure. You must not re-r > discipline even with the same data or your computer again will be eaten by > demons. > > -In order to remove a line discipline call tty_register_ldisc passing NULL. > +In order to remove a line discipline call tty_unregister_ldisc(). > In ancient times this always worked. In modern times the function will > return -EBUSY if the ldisc is currently in use. Since the ldisc referencing > code manages the module counts this should not usually be a concern. > diff -uprN linux-tty_register_ldisc_000/drivers/char/tty_io.c linux-tty_register_ldisc_001/drivers/char/tty_io.c > --- linux-tty_register_ldisc_000/drivers/char/tty_io.c 2005-05-31 20:13:34.000000000 +0400 > +++ linux-tty_register_ldisc_001/drivers/char/tty_io.c 2005-05-31 23:17:40.000000000 +0400 > @@ -262,17 +262,10 @@ int tty_register_ldisc(int disc, struct > return -EINVAL; > > spin_lock_irqsave(&tty_ldisc_lock, flags); > - if (new_ldisc) { > - tty_ldiscs[disc] = *new_ldisc; > - tty_ldiscs[disc].num = disc; > - tty_ldiscs[disc].flags |= LDISC_FLAG_DEFINED; > - tty_ldiscs[disc].refcount = 0; > - } else { > - if(tty_ldiscs[disc].refcount) > - ret = -EBUSY; > - else > - tty_ldiscs[disc].flags &= ~LDISC_FLAG_DEFINED; > - } > + tty_ldiscs[disc] = *new_ldisc; > + tty_ldiscs[disc].num = disc; > + tty_ldiscs[disc].flags |= LDISC_FLAG_DEFINED; > + tty_ldiscs[disc].refcount = 0; > spin_unlock_irqrestore(&tty_ldisc_lock, flags); > > return ret; > @@ -280,6 +273,26 @@ int tty_register_ldisc(int disc, struct > > EXPORT_SYMBOL(tty_register_ldisc); > > +int tty_unregister_ldisc(int disc) > +{ > + unsigned long flags; > + int ret = 0; > + > + if (disc < N_TTY || disc >= NR_LDISCS) > + return -EINVAL; > + > + spin_lock_irqsave(&tty_ldisc_lock, flags); > + if (tty_ldiscs[disc].refcount) > + ret = -EBUSY; > + else > + tty_ldiscs[disc].flags &= ~LDISC_FLAG_DEFINED; > + spin_unlock_irqrestore(&tty_ldisc_lock, flags); > + > + return ret; > +} > + > +EXPORT_SYMBOL(tty_unregister_ldisc); > + > struct tty_ldisc *tty_ldisc_get(int disc) > { > unsigned long flags; > diff -uprN linux-tty_register_ldisc_000/include/linux/tty.h linux-tty_register_ldisc_001/include/linux/tty.h > --- linux-tty_register_ldisc_000/include/linux/tty.h 2005-05-31 20:15:51.000000000 +0400 > +++ linux-tty_register_ldisc_001/include/linux/tty.h 2005-05-31 23:18:23.000000000 +0400 > @@ -345,6 +345,7 @@ extern int tty_check_change(struct tty_s > extern void stop_tty(struct tty_struct * tty); > extern void start_tty(struct tty_struct * tty); > extern int tty_register_ldisc(int disc, struct tty_ldisc *new_ldisc); > +extern int tty_unregister_ldisc(int disc); > extern int tty_register_driver(struct tty_driver *driver); > extern int tty_unregister_driver(struct tty_driver *driver); > extern void tty_register_device(struct tty_driver *driver, unsigned index, struct device *dev); > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- -- Paul Fulghum paulkf@microgate.com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/