Re: Dumping Large Binary Buffer Through Sysctl

In message <5D267A3F22FD854F8F48B3D2B52381933936483700_at_IRVEXCHCCR01.corp.ad.bro
adcom.com>, "David Christensen" writes:
>> >I'm looking for a way to dump a large binary debug buffer=3D20
>> >in a driver to a file.  I've currently implemented this
>> >with SYSCTL_ADD_OPAQUE() and it works fine but running the
>> >"sysctl -a" command causes this buffer to be dumped which
>> >is something of a pain.  Is there a better way to do this?
>>=20
>> Much better idea:  memory map it, that way your driver does
>> not even discover that userland peeks over its shoulder.
>
>I found the CTLFLAG_SKIP attribute which hides the sysctl and=20
>makes things a lot better.  How do I "memory map" the buffer?
>Can you give me a function name or point to an example where=20
>this is done so I can look into it further?

You implemente a cdevsw->mmap() function that tells the kernel
where it is, then in userland, you open the device and
call mmap(2).

See sys/kern/subr_devstat.c for an example.



-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk_at_FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.