Date: Mon, 12 Jan 2015 10:01:03 -0700 From: Warner Losh <imp@bsdimp.com> To: John Baldwin <jhb@FreeBSD.org> Cc: Hans Petter Selasky <hps@selasky.org>, arch@freebsd.org Subject: Re: devctl(8): A device control utility Message-ID: <11219A27-4C5B-4429-8847-3E54F9C4CD1E@bsdimp.com> In-Reply-To: <54B3F349.9050703@FreeBSD.org> References: <3200196.9ZgXApgRdA@ralph.baldwin.cx> <54AAF60A.9070609@FreeBSD.org> <54AAFAEB.2090505@selasky.org> <6155572.yV5dxPJznD@ralph.baldwin.cx> <54B3F349.9050703@FreeBSD.org>
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[-- Attachment #1 --] > 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... Warner [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQIcBAEBCgAGBQJUs/3PAAoJEGwc0Sh9sBEArfwP/2oRtY/d7tvFxbZ4C5+w77tt MPzQhy2V21ehXlba3oPiefx7Nck8XV8koW4W44VuxFKw84q477TOnUPsMGK/3JN4 cQw6WUXcWn7Z8kAmd3dQv3UGSnO44Tg64WFYdTSczluqOvBxocGGY9d5WaC2U/Qo lG99tq7xwcwmvNYz4Hw2DkN5puwJ38IXyFyDl826oz9JIuKhCToRSOncWLIpJfPL 4B9LxZeGyY4f1XXn1ABQiRHk6osGvAf0VEMrUyyRQ3BYAwNyGFesoOJU3FGc1a1i VTHrdKgp8MZNAzKw4IbNeYOCPkhYVOAE1VbKxx4GsKLKJ6Sm1vS3IxoKXDJup+1S IvDeVXKI9P4yalyVu2llaT116mYaaxJ2jj9hZT2woFIPy5qg753SfTSK3zVBHpwe OWbbSguFILcbSh4hxBRxbsMVySeL+CQ4VOgzG+V0MLb7+hyQG0DbWJENRdNuRxNe MYO6Zwwltwk81CE6GiTlzT26+trWKyUsqQ4EONLs1FTq3E8JBwYb1MYWKXLtFV4h 97bCzkdf880jrb89gOAEaASvEiCyJCyMbPYSVrwpR+bTyTDJK6FYWeBiSXu4G3hk q7Dl7xJkuiydodNLNlk2jLCD/6gbCGpHu1TfiKZqmMseyIt3huoOMtuTs+4NTiqf zXEFtYopM+QNnVqkx0w0 =Wv8m -----END PGP SIGNATURE-----
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