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 [off-list ref] wrote:

quoted

Lucas De Marchi [off-list ref] writes:

quoted

On Wed, Feb 18, 2015 at 2:07 AM, Rusty Russell [off-list ref] 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.

quoted

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.

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.

So please just wait for the event, then you should be fine, that's what
it is there for.

thanks,

greg k-h