Date: Tue, 21 Jul 2009 17:07:13 -0700 From: Alfred Perlstein <alfred@freebsd.org> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-drivers@freebsd.org Subject: Re: Driver development question Message-ID: <20090722000713.GZ49724@elvis.mu.org> In-Reply-To: <200907211743.12667.jhb@freebsd.org> References: <002801ca06f0$b1d42af0$157c80d0$@net> <4A64F200.2060900@errno.com> <200907210834.21541.marc.loerner@hob.de> <200907211743.12667.jhb@freebsd.org>
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* John Baldwin <jhb@freebsd.org> [090721 14:44] wrote: > On Tuesday 21 July 2009 2:34:21 am Marc Loerner wrote: > > Am Dienstag 21 Juli 2009 00:38:56 schrieb Sam Leffler: > > > John Baldwin wrote: > > > > On Friday 17 July 2009 11:10:17 am Chris Harrer wrote: > > > >> Hi All, > > > >> > > > >> I'm hoping someone can point me in the right direction... I'm > > > >> developing a FreeBSD driver for a PCIe card. The driver controls a > > > >> hardware device that has DRAM and various state information on it. I'm > > > >> trying to mimic functionality I have for other OS support such that I > > > >> can dump memory and state information from the card to a file I create > > > >> from within my driver (kernel module). > > > >> > > > >> For example, in a Linux driver I use filp_open to create the dump file > > > >> (represented by fp), then use fp->f_op->write to put information into > > > >> the file. > > > >> > > > >> FreeBSD doesn't have filp_* API's. I've tried searching for example > > > >> drivers and googling for file API's from kernel modules to no avail. > > > >> Can someone please offer some guidance as to how I might proceed here? > > > >> > > > >> Thanks in advance and any insight would be most appreciated! > > > > > > > > You can look at sys/kern/kern_ktrace.c to see how the ktrace() system > > > > call creates a file. I think in general you will wind up using > > > > NDINIT/namei() (to lookup the vnode for a pathname) and then vn_open() / > > > > vn_rdwr() / vn_close(). > > > > > > man alq(9). > > > > > > > > > > Why not use kern_open, kern_close, kern_preadv, kern_pwritev? > > Those affect the state of the current process by opening a new file > descriptor, etc. That is generally bad practice for a device driver to be > interfering with a process' state, and it will not work for kernel threads. > You can rather easily have userland open a file and then pass the file > descriptor to a driver which can then do operations on a file directly. If the vnode operations are annoying to wrap ones head around, one could have the driver defer this this to a kernel resident process that the driver would create on attach. -- - Alfred Perlstein VMOA #5191, 03 vmax, 92 gs500, ch250 - FreeBSD
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