On Wed, Aug 28, 2013 at 11:53:06AM -0700, Greg Kroah-Hartman wrote: > On Wed, Aug 28, 2013 at 11:44:33AM -0700, Guenter Roeck wrote: > > On Wed, Aug 28, 2013 at 11:31:39AM -0700, Greg Kroah-Hartman wrote: > > > On Wed, Aug 28, 2013 at 10:57:17AM -0700, Guenter Roeck wrote: > > > > Hi, > > > > > > > > I noticed that gpiolib does not explicitly remove the sysfs attributes > > > > it > > > > created when exporting a gpio pin when the pin is unexported, ie when > > > > the > > > > associated device is removed. > > > > > > > > Are those attributes auto-removed when device_unregister() is called ? > > > > > > Yes they are. > > > > > Does that mean that the explicit attribute removal that is implemented > > in many drivers can be dropped ? That might save a lot of code. > > Yes, they could be dropped, but I think it's nicer to be explicit about > this. Originally, it could be a long time before the kernel would > remove the sysfs device from the tree, so removing the files could cause > problems as the callbacks would happen for a device that the driver was > not expecting to be present. > > Also, if a driver is "unbound" from a device, and the device sticks > around, the sysfs files are not removed automatically, it's up to the > driver to remove them, so it's good practice to remove them. > > > > > Sorry if this is a dumb question - I have not noticed this anywhere > > > > else, > > > > and I don't seem to be able to find the code actually performing > > > > auto-removal > > > > of manually created attributes, so I wonder if this is a bug or > > > > intentional. > > > > > > Hm, I thought this was listed in the kobject.txt documentation file, but > > > I don't seem to find it there. > > > > > Would be great if this could be documented somewhere (unless it is and > > I didn't find it ;). I would volunteer to do it myself, but I have no idea > > what the conditions for auto-removal are nor how to phrase it, nor where > > to put it. > > When the kobject is removed from the system, the sysfs files attached to > it are also removed. That could go into kobject.txt somewhere, but the > attributes are what need to be highlighted, and used, so that's a better > thing to focus on at the moment. > > > > But, ideally you aren't creating individual attributes directly, you are > > > using attribute groups for the device, right? > > > > > gpiolib does currently create individual attributes as well as attribute > > groups after registering the device. I was in the process of converting > > it to use device_create_with_groups() when I noticed that there is no > > removal, so I wondered. > > The driver core will remove the attributes at the point the device goes > away, no need to remove them on your own here at all. > > > I take it that attribute groups created with sysfs_create_group() > > are auto-removed as well, correct ? > > Yes they are, but no driver, or subsystem, should be making that call, > they should be using the driver core pointers for attributes instead to > properly handle the lifespan of the attributes for the device. > A good reason to use device_create_with_groups() instead of creating attributes manually.
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