Messages in this thread | | | Date | Fri, 30 Jan 2015 17:31:51 +0100 | From | Takashi Iwai <> | Subject | Re: [PATCH 0/2] Add device_create_files() and device_remove_files() helpers |
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At Thu, 29 Jan 2015 20:26:26 -0800, Greg Kroah-Hartman wrote: > > 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.
The latter one (regulator/core.c) is actually a case where is_visible callback would work better, I noticed after studying mode code. Thanks for hints. I'm going to submit a patch later.
OTOH, the leds class looks not intuitive. Need more investigation.
> > 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.
If we export device_add_groups() and device_remove_groups(), is it safe to call it before device_add()? If yes, some drivers/subsystems can have a code flow like:
some_subsystem_init(struct device *dev) { device_initialize(dev); devs->groups = subsystem_groups; .... }
driver_init(struct device *dev) { some_subsystem_init(dev); device_add_groups(dev, additional_groups); .... device_add(dev); .... }
The network device has a own multi dev_groups array so that the driver can put an own group while the net core fills common groups dynamically just before the device registration call. I though of implementing similar for others (including the sound stuff), but if the scheme above works, the rewrite will become smaller.
Of corse, the drawback of the explicit device_add_groups() call would be that you'll have to call device_remove_groups() at removal or error paths.
> > > > 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.
Right, there are a bunch of drivers doing it. I guess partly because they don't need uevents for creation, but also partly because there is no way to give attribute groups properly in some cases. For example, misc_register() or register_framebuffer() calls device_create() so the caller can't pass groups.
It'd be trivial to extend struct miscdevice to carry an optional group field and change the call to device_create_with_groups(). But, fb_info has also common sysfs entries, so it'd need also the solution above with device_add_groups() in addition.
The similar pattern is found for many drivers with platform devices. But I haven't figured out yet what would be a good way...
thanks,
Takashi
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