svn commit: r239178 - in head/sys: kern sys

[John Baldwin]

On Monday, August 13, 2012 3:43:42 pm Hans Petter Selasky wrote:
> On Monday 13 August 2012 15:49:07 John Baldwin wrote:
> > On Friday, August 10, 2012 11:02:50 am Hans Petter Selasky wrote:
> > > Author: hselasky
> > > Date: Fri Aug 10 15:02:49 2012
> > > New Revision: 239178
> > > URL: http://svn.freebsd.org/changeset/base/239178
> > > 
> > > Log:
> > >   Add new device method to free the automatically
> > >   allocated softc structure which is returned by
> > >   device_get_softc(). This method can be used to
> > >   easily implement softc refcounting. This can be
> > >   desirable when the softc has memory references
> > >   which are controlled by userspace handles for
> > >   example.
> > 
> > Why do you need a new method?  If you want to manage your own softc, you
> > are free to do so by using a size of 0 in your driver_t.  You can then use
> > device_set_softc() to set the softc during your attach routine.  New-bus
> > won't free it during detach leaving you to free it instead.  That is what
> > you should have done here instead of polluting device_if.m.  Note that
> > DF_EXTERNALSOFTC is an internal flag to explicitly handle this case, but
> > you've now made it possible for a device to try to do special free logic
> > but haven't made DF_EXTERNALSOFTC visible to that driver.  This is why I
> > think new-bus already let you do what you wanted (via device_set_softc())
> > and think you should just do that and back this out.
> 
> Hi,
> 
> I know that drivers can manage their own softc's, only that it will add 5-10 
> more lines of code and error handling to each UCOM client driver, instead of 
> using the .size field which factors all of this out of the driver.

I don't think you need 5-10 lines, more like 1 or 2.  This:

struct driver_t {
	...
	sizeof(struct foo_softc)
};

int
foo_attach(device_t dev)
{
	struct foo_softc *sc;

	sc = device_get_softc(dev);
	...
}

becomes:

struct driver_t {
	...
	0
};

int
foo_attach(device_t dev)
{
	struct foo_softc *sc;

	sc = malloc(sizeof(struct foo_softc), M_BUS, M_WAITOK | M_ZERO);
	device_set_softc(dev, sc);
	...
}

-- 
John Baldwin