linux-kernel - Re: [PATCH 12/12] usb: use IRQ watching

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Message-ID: <AANLkTinnpbSVfA1vWWDdVHy0UpLh-SlAXXg0o54OgXFi@mail.gmail.com>
Date:	Tue, 15 Jun 2010 15:30:14 +0200
From:	Kay Sievers <kay.sievers@...y.org>
To:	Jean Delvare <khali@...ux-fr.org>
Cc:	Tejun Heo <tj@...nel.org>, Greg KH <gregkh@...e.de>, mingo@...e.hu,
	tglx@...utronix.de, bphilips@...e.de, yinghai@...nel.org,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org, jeff@...zik.org,
	linux-ide@...r.kernel.org, stern@...land.harvard.edu
Subject: Re: [PATCH 12/12] usb: use IRQ watching

On Tue, Jun 15, 2010 at 13:05, Jean Delvare <khali@...ux-fr.org> wrote:
> On Tue, 15 Jun 2010 12:30:00 +0200, Kay Sievers wrote:
>> On Tue, Jun 15, 2010 at 00:19, Tejun Heo <tj@...nel.org> wrote:
>> > Hmm... maybe what we can do is generating an uevent when an IRQ is
>> > confirmed to be bad and then let udev notify the user.  That way we'll
>> > probably have better chance of getting bug reports and users have
>> > whiny but working system.
>>
>> Not really, uevents are not picked up by anything that could report an
>> error to userspace, they are just seen by udev. Also uevents are
>> usually not the proper passing method. They are not meant to ever
>> transport higher frequency events, or structured data. They cause to
>> run the entire udev rule matching machine, and update symlinks and
>> permissions with every event.
>>
>> We will need some better error reporting facility. On Linux you don't
>> even get notified when the kernel mounts your filesystem read-only
>> because of an error. It will only end up in 'dmesg' as a pretty much
>> undefined bunch of words. :)
>>
>> We will need some generic error reporting facility, with structured
>> data exported, and where userspace stuff can subscribe to.
>> Uevents/udev can not really properly provide such infrastructure.
>> Maybe that can be extended somehow, but using kobject_uevent() and
>> trigger the usual udev rule engine is not what we are looking for, for
>> sane error reporting.
>
> Random idea of the day (I don't know anything about it all): let the
> kernel connect to D-Bus and use it somehow?

Yeah, D-Bus is an peer-to-peer IPC mechanism/protocol. The D-Bus
daemon can filter and multiplex/distibute messages.

It's very similar to what we can do with netlink. The netlink
multicast stuff can even provide lots of the functionality the D-Bus
daemon provides.

I think we should avoid the D-Bus complexity for the very low-level
stuff. Very much like udev is not using it, but has efficient
in-kernel message filtering based on Berkeley Packet Filters, and
multiple listeners event subscription/distribution based on netlink
multicast functionality.

Not sure if netlink is the right answer here, but it's surely easier
to handle than D-Bus, and would provide a very similar functionality.

Kay
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