Driver development question

[John Baldwin]

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.

-- 
John Baldwin