Date: Fri, 24 Jul 2009 20:56:43 -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: <20090725035643.GT49724@elvis.mu.org> In-Reply-To: <200907220819.05087.jhb@freebsd.org> References: <002801ca06f0$b1d42af0$157c80d0$@net> <200907211743.12667.jhb@freebsd.org> <20090722000713.GZ49724@elvis.mu.org> <200907220819.05087.jhb@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
* John Baldwin <jhb@freebsd.org> [090722 06:21] wrote: > On Tuesday 21 July 2009 8:07:13 pm Alfred Perlstein wrote: > > * 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. > > Kernel processes don't have file descriptor tables. they do when you use an analogue to the old nfsd() syscall mechanism. -- - Alfred Perlstein VMOA #5191, 03 vmax, 92 gs500, ch250 - FreeBSD
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20090725035643.GT49724>