Messages in this thread | | | Date | Thu, 29 Jan 2015 20:26:26 -0800 | From | Greg Kroah-Hartman <> | Subject | Re: [PATCH 0/2] Add device_create_files() and device_remove_files() helpers |
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On Thu, Jan 29, 2015 at 12:11:21AM +0100, Takashi Iwai wrote: > At Wed, 28 Jan 2015 14:28:51 -0800, > Greg Kroah-Hartman wrote: > > > > On Wed, Jan 28, 2015 at 11:18:57PM +0100, Takashi Iwai wrote: > > > At Wed, 28 Jan 2015 13:34:21 -0800, > > > Greg Kroah-Hartman wrote: > > > > > > > > On Wed, Jan 28, 2015 at 10:26:28PM +0100, Takashi Iwai wrote: > > > > > At Wed, 28 Jan 2015 13:05:47 -0800, > > > > > Greg Kroah-Hartman wrote: > > > > > > > > > > > > On Wed, Jan 28, 2015 at 09:46:12PM +0100, Takashi Iwai wrote: > > > > > > > Hi, > > > > > > > > > > > > > > this is a simple patch to add device_create_files() and > > > > > > > device_remove_files() to replace multiple device_create_file() or > > > > > > > _remove() calls with a single shot with the device_attr list. > > > > > > > > > > > > > > It's basically just a clean up, but also helps to simplify the error > > > > > > > handling a lot in many existing codes since the function itself does > > > > > > > rollback at error. > > > > > > > > > > > > > > The series contains a patch to apply these to drivers/base/node.c. > > > > > > > I have lots of patches (up to 30) to use these in the whole tree, but > > > > > > > maybe it'd be easier too apply once after this stuff is merged at > > > > > > > first. It's just a cleanup so no urgent task, after all. > > > > > > > > > > > > I'd like to some day be able to drop device_create_file entirely, as it > > > > > > is almost always used in a racy way (but not always, so we can't get rid > > > > > > of it today.) > > > > > > > > > > > > A driver should be using an attribute group and be created/registered > > > > > > with it if they want any files associated with it, so giving people the > > > > > > ability to add large numbers of files all at once seems like the wrong > > > > > > thing to do :) > > > > > > > > > > Well, through the glance over many codes using device_create_file(), > > > > > I think the problem of the attribute group is that there is little > > > > > help for generating the entries dynamically. For example, if you have > > > > > two groups you want to enable conditionally, what would be the best > > > > > way to implement? > > > > > > > > Use the is_visable() function callback, that's what it is there for. > > > > > > But if the entries are determined dynamically? Selecting the enabled > > > elements from the static list is one way, it'd work in many cases, but > > > it's not always the most straightforward way. It often would be > > > easier to build up the list dynamically. > > > > Do you have an example of this? Wouldn't it be the same thing to list > > them all in an attribute group, but only say "this is valid" in the > > is_visable() callback for those that would have been built up > > dynamically? > > One common scene is the case where a device has already the static > group defined in the core helper module while a driver wants to put > additional sysfs entries on it. > > A complex case is something in drivers/leds/trigger/ledtrig-*.c. > > Another interesting example is drivers/regulator/core.c. It creates a > bunch of various sysfs files depending on the client's ops presence. > It might be implemented via is_visible, but then it'd become more > lengthy (too many small callback functions).
Yeah, I'm not saying it's easy, or simple, it's just the only way I know how to do this in a race-free way. We have to create the files before the uevent happens, not after, like these drivers are doing.
If you can think of a way that we can do this in a simpler way, that would be great.
> Also, multiple drivers seem calling device_create_file() from the > array of attributes in a loop. One reason might be that it's easier > to write for a bunch of entries, without defining many piece of > structs. An example is found in drivers/gpu/drm/drm_sysfs.c.
That one should just be adding the whole attribute group, using device_add_groups, which we have in the driver core, but I didn't export publicly. That is if those are being added in a race-free way, I couldn't unwind the drm mess to see if the uevent is happening after the files are added or before.
> > > What if having a link to the chained group for appending entries > > > dynamically? Just a wild idea, but it might make things easier. > > > > We have the ability to pass a group list pointer to device_create > > already, and the attribute pointer is a list of groups as well, how can > > we change this to be "easier"? > > I guess the order is the problem. In many cases, you know the > additional entries only after the device creation. The device > creation is often done by a helper code. So the driver has no control > to it, just gets the resultant device.
Yeah, that's the problem. And another problem is drivers adding attributes to devices after they are bound to a device, which is kind of pointless, as the uevent is long past at that point in time. I've cleaned up a bunch of those, but odds are there are still more to fix.
thanks,
greg k-h
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