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SubjectRe: [PATCH mm] sysfs: add /sys/dev/usb to handle CONFIG_USB_DEVICE_CLASS=y
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On Thu, 2008-04-17 at 21:59 -0700, Dan Williams wrote:
> On Thu, Apr 17, 2008 at 8:21 PM, Greg KH <greg@kroah.com> wrote:
> > On Thu, Apr 17, 2008 at 07:11:03PM -0700, Dan Williams wrote:
> >
> > > The deprecated config option CONFIG_USB_DEVICE_CLASS causes class devices
> > > with duplicate major:minor numbers to be registered. In effect they
> > > represent a usb specific address space for major:minor numbers so add 'usb'
> > > as a directory along side 'block' and 'char'.
> >
> > Hm, no they do not, they are not a new address space, we are just
> > reusing them as the other user wasn't using them, and the code is
> > deprecated and will be removed eventually. Neither of these char
> > devices are really hooked up to anything within the kernel, so it
> > doesn't matter yet.
> >
> > I wonder how many other duplicates we have floating around...
> >
>
> Hm, so how about making this an opt-in capability of the class? At
> device_add() time the class is queried to see if a link should be
> created in /sys/dev/block or /sys/dev/char?

This could work, yes. We could just set a flag in the class, that
prevents the device entries in /sys/dev/.

> Although, this leads to
> inconsistent coverage. But maybe that does not matter as many of
> these character devices do not have interesting attributes to be
> accessed?

The usual case is that one of the duplicated /sys devices is deprecated,
so it should be fine, to always point to the new one.

> Sigh, I am beginning to wonder if the character device side
> of this capability is a solution looking for a problem...

We will find a solution. :)

The following should work for the common case.

Best,
Kay


From: Kay Sievers <kay.sievers@vrfy.org>
Subject: sysfs: fix duplicated device number registration in /sys/dev/

If the parent device has the same dev_t, we skip the registration
for the device number at /sys/dev.

Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Greg KH <greg@kroah.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
---

core.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index de925f8..afedadb 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -821,10 +821,13 @@ int device_add(struct device *dev)
if (error)
goto ueventattrError;

- format_dev_t(devt_str, dev->devt);
- error = sysfs_create_link(kobj, &dev->kobj, devt_str);
- if (error)
- goto devtattrError;
+ /* do not create /sys/dev/ entry if parent already did */
+ if (!(dev->parent && dev->parent->devt == dev->devt)) {
+ format_dev_t(devt_str, dev->devt);
+ error = sysfs_create_link(kobj, &dev->kobj, devt_str);
+ if (error)
+ goto devtattrError;
+ }
}

error = device_add_class_symlinks(dev);
@@ -950,8 +953,10 @@ void device_del(struct device *dev)
if (parent)
klist_del(&dev->knode_parent);
if (MAJOR(dev->devt)) {
- format_dev_t(devt_str, dev->devt);
- sysfs_remove_link(device_to_dev_kobj(dev), devt_str);
+ if (!(parent && parent->devt == dev->devt)) {
+ format_dev_t(devt_str, dev->devt);
+ sysfs_remove_link(device_to_dev_kobj(dev), devt_str);
+ }
device_remove_file(dev, &devt_attr);
}
if (dev->class) {

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