Re: [PATCH] ACPI: dock: Don't eval _STA on every show_docked sysfs read

[Len Brown <lenb@kernel.org>]

--
Len Brown, Intel Open Source Technology Center

On Tue, 27 Jan 2009, Andrew Morton wrote:

> On Tue, 20 Jan 2009 12:18:24 +0100
> Holger Macht <hmacht@suse.de> wrote:
> 
> > Cc: stable@kernel.org
> 
> The patch applied OK to 2.6.28 but not to any earlier kernel.  If we
> decide that it should be backported to 2.6.27 or earlier, a new patch
> might be needed for that.
> 
> > Some devices trigger a DEVICE_CHECK on every evalutation of _STA. This
> > can also be seen in commit 8b59560a3baf2e7c24e0fb92ea5d09eca92805db
> > (ACPI: dock: avoid check _STA method).  If an undock is processed, the
> > dock driver sends a uevent and userspace might read the show_docked
> > property in sysfs. This causes an evaluation of _STA of the particular
> > device which causes the dock driver to immediately dock again.
> > 
> > In any case, evaluation of _STA (show_docked) does not necessarily mean
> > that we are docked, so check with the internal device structure.
> > 
> > http://bugzilla.kernel.org/show_bug.cgi?id=12360
> > 
> > Signed-off-by: Holger Macht <hmacht@suse.de>
> > ---
> > 
> > diff --git a/drivers/acpi/dock.c b/drivers/acpi/dock.c
> > index 5b30b8d..afd5db3 100644
> > --- a/drivers/acpi/dock.c
> > +++ b/drivers/acpi/dock.c
> > @@ -855,10 +855,14 @@ fdd_out:
> >  static ssize_t show_docked(struct device *dev,
> >  			   struct device_attribute *attr, char *buf)
> >  {
> > +	struct acpi_device *tmp;
> > +
> >  	struct dock_station *dock_station = *((struct dock_station **)
> >  		dev->platform_data);
> > -	return snprintf(buf, PAGE_SIZE, "%d\n", dock_present(dock_station));
> >  
> > +	if (ACPI_SUCCESS(acpi_bus_get_device(dock_station->handle, &tmp)))
> > +		return snprintf(buf, PAGE_SIZE, "1\n");
> > +	return snprintf(buf, PAGE_SIZE, "0\n");
> >  }
> >  static DEVICE_ATTR(docked, S_IRUGO, show_docked, NULL);
> 
> That seems a little overwrought.  Won't plain old strcpy suffice?
> 
> 
> --- a/drivers/acpi/dock.c~acpi-dock-dont-eval-_sta-on-every-show_docked-sysfs-read-simplification
> +++ a/drivers/acpi/dock.c
> @@ -861,8 +861,8 @@ static ssize_t show_docked(struct device
>  		dev->platform_data);
>  
>  	if (ACPI_SUCCESS(acpi_bus_get_device(dock_station->handle, &tmp)))
> -		return snprintf(buf, PAGE_SIZE, "1\n");
> -	return snprintf(buf, PAGE_SIZE, "0\n");
> +		return strcpy(buf, "1\n");
> +	return strcpy(buf, "0\n");
>  }
>  static DEVICE_ATTR(docked, S_IRUGO, show_docked, NULL);
>  
> _
> 

sure, strcpy is fine b/c the src and dest are known to not be in danger of 
overlow.  applied to acpi misc branch.

thanks,
-Len