Driver development question

[Sam Leffler]

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?

These require a process context.  alq is designed for exactly what the 
OP wants.  The writes are non-blocking and can be done from interrupt 
context.  The only (current) limitation is records must be fixed size 
but that's easy to deal with.

I use alq to trace register r/w operations in a driver and it works 
great (low overhead so doesn't noticeably affect real-time operation). 
In fact it works so well that I ported the code to linux (you can find 
it in the madwifi code base).

	Sam