Date: Mon, 12 Jan 2015 17:01:44 -0500 From: John Baldwin <jhb@FreeBSD.org> To: Warner Losh <imp@bsdimp.com> Cc: Hans Petter Selasky <hps@selasky.org>, arch@freebsd.org Subject: Re: devctl(8): A device control utility Message-ID: <54B44448.1090901@FreeBSD.org> In-Reply-To: <11219A27-4C5B-4429-8847-3E54F9C4CD1E@bsdimp.com> References: <3200196.9ZgXApgRdA@ralph.baldwin.cx> <54AAF60A.9070609@FreeBSD.org> <54AAFAEB.2090505@selasky.org> <6155572.yV5dxPJznD@ralph.baldwin.cx> <54B3F349.9050703@FreeBSD.org> <11219A27-4C5B-4429-8847-3E54F9C4CD1E@bsdimp.com>
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On 1/12/15 12:01 PM, Warner Losh wrote: > >> On Jan 12, 2015, at 9:16 AM, John Baldwin <jhb@FreeBSD.org> wrote: >> >> On 1/5/15 4:18 PM, John Baldwin wrote: >>> On Monday, January 05, 2015 09:58:19 PM Hans Petter Selasky wrote: >>>> On 01/05/15 21:37, John Baldwin wrote: >>>>> On 1/5/15 3:13 PM, Hans Petter Selasky wrote: >>>>>> On 01/05/15 21:01, John Baldwin wrote: >>>>>>> The devctl(8) utility is then a thin wrapper around libdevctl (and >>>>>>> does not >>>>>>> yet have a manpage). >>>>>>> >>>>>>> Do folks have any feedback? >>>>>> >>>>>> Hi, >>>>>> >>>>>> In the USB area attach and detach must be synchronized to the USB stack >>>>>> and "usbconfig -d X.Y set_config Z" or "usbconfig -d X.Y reset" should >>>>>> be used to avoid races attaching and detaching drivers! >>>>> >>>>> I think this points to one or more missing bus methods so that the bus >>>>> can hook into device_probe_and_attach() to reset a device as needed. >>>>> (e.g. if you had bus_probe_started / bus_probe_finished and possibly >>>>> similar methods for attach. PCI could use a bus_attach_finished() >>>>> callback so that it could clean up any dangling resources and possibly >>>>> power down on a failed attach the way it does in bus_child_detached as >>>>> well). >>>> >>>> Hi, >>>> >>>> USB has its own threads to allocate/free devices. Another problem is how >>>> to atomically get a reference count across multiple layers like PCI and >>>> USB. It doesn't allow probe/attach when called from outside these threads. >>> >>> That just means you need to use some locks. :) Cardbus also uses an event >>> thread to handle auto-attach of devices when it detected a card change event, >>> but that doesn't prevent it from servicing an ioctl request. >> >> Another option btw would be to add bus methods that wrap probe and >> attach (rather than pre and post event hooks). I wish bus_add_child() >> were done this way such that device_add_child_ordered() were renamed to >> bus_generic_add_child() (and was the default add_child method) and that >> device_add_child_ordered() called 'BUS_ADD_CHILD()' so that >> 'device_add_child()' was the proper public API (instead of exposing >> BUS_ADD_CHILD()). Similarly, I think that 'device_attach()' and >> 'device_probe_and_attach()' should be the public API and that one way or >> another we should add hooks to allow bus drivers to modify their >> behavior if needed. However, they should be fine for devctl ioctls to >> invoke as well as other kernel bits. > > When I was doing CardBus and PC Card I wished for similar things. Then > I realized I didn’t need them because as the bus author, I know when these > events happened and could take appropriate actions for the bus. I didn’t have > that atomic access issues though, since as the bus author I also controlled how > and when mutexes were taken out and when I allowed access to the bus. I > only used mutexes in CardBus and PC Card because most of the sleeps were > short, but other ways to do locking are quite possible... I think the problem here is that devctl introduces events that happen without the bus's knowledge. -- John Baldwin
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