On Thu, Feb 19, 2015 at 12:25 AM, greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > On Wed, Feb 18, 2015 at 11:19:14PM -0200, Lucas De Marchi wrote: >> On Wed, Feb 18, 2015 at 8:40 PM, Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote: >> > Lucas De Marchi <lucas.de.marchi@xxxxxxxxx> writes: >> >> On Wed, Feb 18, 2015 at 2:07 AM, Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote: >> >> Yeah, I just thought (an wanted that) the attributes were being >> >> created first and then hooked up in the sysfs tree under >> >> /sys/module/<modulename>. I.e. if the directory exists and there's no >> >> initstate this is because it's a builtin module. I don't want to >> >> wait/sleep on the file to appear because users of >> >> kmod_module_get_initstate() may not tolerate this behavior. >> >> >> >> Looking up at the old module-init-tools, it used an ugly loop with >> >> usleep() before trying to read the file again :-/ >> >> >> >> Can we change kernel side guaranteeing the initstate file appears >> >> together with the directory? >> > >> > Greg? The core problem is that kmod looks for >> > /sys/module/<name>/initstate; if it's not there, it assumes a builtin >> > module. >> >> Just to make it clear: >> >> We try to open /sys/module/<name>/initstate. If it fails we stat >> /sys/module/<name> checking if it exists and is a directory. If it >> does then we assume the module is builtin. >> >> > However, this is racy when a module is being inserted. Is there a way >> > to create this sysfs file and dir atomically? >> >> Greg, the question is still valid since it'd be nice to have this >> guarantee and be able to correctly reply the state with whatever is in >> initstate file, but... > > You should always wait until you get the uevent that the object was > added before poking around in sysfs. The kernel will guarantee all of > the needed files / directories will be created before that event is sent > out. That's why we added the uevent message. for kmod I think I prefer the alternative of not needing it at all... for daemons and other tools it makes sense indeed. > So by just busy-spinning on the directory and ignoring the uevent, you > are just blindly guessing as to when things are finished, which is racy > as you see. note there's no busy-spinning in kmod.... this was in module-init-tools and it's what I'm saying I don't want to do. Not something you want in a library. -- Lucas De Marchi -- To unsubscribe from this list: send the line "unsubscribe linux-modules" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
