Re: [PATCH] Disable /dev/port interface on powerpc systems

[Haren Myneni <haren@linux.vnet.ibm.com>]

On Wed, 2012-03-21 at 18:23 +1100, Benjamin Herrenschmidt wrote:
> On Tue, 2012-03-20 at 22:37 -0700, Haren Myneni wrote:
> > Some power systems do not have legacy ISA devices. So, /dev/port is not
> > a valid interface on these systems. User level tools such as kbdrate is
> > trying to access the device using this interface which is causing the
> > system crash. 
> > 
> > This patch will fix this issue by not creating this interface on these
> > powerpc systems. 
> 
> Doesn't fix 32-bit... not a big deal for now I suppose... But I'd rather
> you change the patch a tiny bit to change legacy_isa_device_found() to
> arch_has_dev_port() instead. There may be other reason than legacy ISA
> to enable dev/port or not so let's make the arch hook more generic.

Thanks for your suggestions. I will make a change and re-post the patch.

> 
> Another approach which might be even better is to filter per-access,
> ie for each read/write to /dev/port, have a hook to check if that
> specific port is valid, but that may be overkill for what is
> essentially a legacy interface that should have died a long time ago :)

Yes, can be changed open or read/write calls and return -ENODEV,
but /dev/port is no use on these systems.

I am not sure whether any power systems have legacy ISA devices. If we
do not have, CONFIG_DEVPORT can be disabled in Kconfig.

--- 
src/drivers/char/Kconfig.orig	2012-03-21 11:05:54.610010864 -0700
+++ src/drivers/char/Kconfig	2012-03-21 11:02:29.750009886 -0700
@@ -596,6 +596,7 @@ config DEVPORT
 	bool
 	depends on !M68K
 	depends on ISA || PCI
+	depends on !PPC64
 	default y


Thanks
Haren

> 
> Cheers,
> Ben.
> 
> > Signed-off-by: Haren Myneni <haren@us.ibm.com>
> > 
> > 
> > diff -Naurp linux.orig/arch/powerpc/kernel/isa-bridge.c
> > linux/arch/powerpc/kernel/isa-bridge.c
> > --- linux.orig/arch/powerpc/kernel/isa-bridge.c	2012-02-11
> > 02:08:08.780005293 -0800
> > +++ linux/arch/powerpc/kernel/isa-bridge.c	2012-02-11 02:16:25.080003386
> > -0800
> > @@ -255,6 +255,14 @@ static struct notifier_block isa_bridge_
> >  	.notifier_call = isa_bridge_notify
> >  };
> >  
> > +int __init legacy_isa_device_found(void)
> > +{
> > +	if (isa_bridge_pcidev)
> > +		return 1;
> > +	
> > +	return 0;
> > +}
> > +
> >  /**
> >   * isa_bridge_init - register to be notified of ISA bridge
> > addition/removal
> >   *
> > diff -Naurp linux.orig/drivers/char/mem.c linux/drivers/char/mem.c
> > --- linux.orig/drivers/char/mem.c	2012-02-11 02:08:42.710002440 -0800
> > +++ linux/drivers/char/mem.c	2012-03-20 20:40:43.650000003 -0700
> > @@ -35,6 +35,8 @@
> >  # include <linux/efi.h>
> >  #endif
> >  
> > +#define DEVPORT_MINOR	4
> > +
> >  static inline unsigned long size_inside_page(unsigned long start,
> >  					     unsigned long size)
> >  {
> > @@ -910,6 +912,11 @@ static char *mem_devnode(struct device *
> >  
> >  static struct class *mem_class;
> >  
> > +int __init __weak legacy_isa_device_found(void)
> > +{
> > +	return 1;
> > +}
> > +
> >  static int __init chr_dev_init(void)
> >  {
> >  	int minor;
> > @@ -930,6 +937,13 @@ static int __init chr_dev_init(void)
> >  	for (minor = 1; minor < ARRAY_SIZE(devlist); minor++) {
> >  		if (!devlist[minor].name)
> >  			continue;
> > +
> > +		/*
> > +		 * Create /dev/port? 
> > +		 */
> > +		if ((minor == DEVPORT_MINOR) && !legacy_isa_device_found())
> > +			continue;
> > +
> >  		device_create(mem_class, NULL, MKDEV(MEM_MAJOR, minor),
> >  			      NULL, devlist[minor].name);
> >  	}
> > diff -Naurp linux.orig/include/linux/isa.h linux/include/linux/isa.h
> > --- linux.orig/include/linux/isa.h	2012-02-11 02:07:52.030019810 -0800
> > +++ linux/include/linux/isa.h	2012-02-11 02:16:49.810002296 -0800
> > @@ -36,4 +36,5 @@ static inline void isa_unregister_driver
> >  }
> >  #endif
> >  
> > +extern int __init legacy_isa_device_found(void);
> >  #endif /* __LINUX_ISA_H */
> > 
> 
> 
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