Debugging an Ioctl Problem on OpenBSD

[hucste]

https://jcs.org/2022/02/16/ioctl

[loeg]

I believe FreeBSD intentionally truncates provided ioctls to the low 32-bit space because of exactly this kind of bogus assumption in userspace:

https://github.com/freebsd/freebsd-src/blob/main/sys/kern/sy...

It's a relatively recent change (2020). Here's the corresponding place OpenBSD doesn't do that:

https://github.com/openbsd/src/blob/master/sys/kern/sys_gene...

[kevin_b_er]

I'm annoyed ktrace wasn't revisited. If the integer was getting truncated, why did ktrace print that the request was still VIDIOC_S_FMT? Shouldn't it have printed some goofy number that didn't match?

[loeg → kevin_b_er]

Kdump truncates to a 32-bit value: https://github.com/openbsd/src/blob/master/usr.bin/kdump/kdu...

[tedunangst → loeg]

Oh! That's dumb. The printer correctly uses unsigned long.

https://github.com/openbsd/src/blob/master/usr.bin/kdump/mki...

[tedunangst → kevin_b_er]

That is weird. I don't see an easy explanation. kdump uses unsigned long.

[adamrt]

Jcs is always doing something cool. Thanks for the write up!

[_dh54 → adamrt]

Indeed. As a programmer desperate for technical edutainment to consume after work, he’s a gem.

[anthk → _dh54]

As an OpenBSD and retro protocol user (gopher, irc, MUDs, and so on) JCS is amazing.

[elvis70]

More people should pay attention to this OS. The source code is so clean and simple compared to Linux.