Date: Tue, 28 Jun 2022 17:18:09 -0400 From: Mark Johnston <markj@freebsd.org> To: Jake Freeland <jake@technologyfriends.net> Cc: freebsd-hackers@freebsd.org Subject: Re: LinuxKPI debugfs Port Message-ID: <YrtwERomNF9FLEzw@nuc> In-Reply-To: <CAOgZAGaQOhxS0oeM-797fHy3Zs1D4A=hnS3uVYqKnzw4HWn8CA@mail.gmail.com> References: <CAOgZAGaQOhxS0oeM-797fHy3Zs1D4A=hnS3uVYqKnzw4HWn8CA@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Tue, Jun 28, 2022 at 03:38:48PM -0500, Jake Freeland wrote: > Hi there, > > I am working on porting Intel's igt-gpu-tools drm graphics driver testing > suite to FreeBSD and I ran into some issues regarding debugfs. I spoke > to manu@ who told me that CONFIG_DEBUG_FS is required for the > testing to work properly. I started working on a debugfs port and quickly > got confused about what manu@ meant by implementing "CONFIG_DEBUG_FS". I would guess that he meant to compile the i915kms driver with CONFIG_DEBUGFS configured. I'm not sure what the "right" way is to do that, but adding KCONFIG+= DEBUGFS to the end of kconfig.mk in the drm-kmod repository seems to do the trick for me, with the caveat that the driver doesn't compile. :) I think the task is to get it to compile by extending the existing debugfs shims in the LinuxKPI, but see my comments below. There is also a typo in the makefile there, see https://github.com/freebsd/drm-kmod/pull/185 > Some quick internet searching says that CONFIG_DEBUG_FS is a > Linux kernel configuration flag. I am curious how I would go about > implementing this into FreeBSD. I copied the Linux debugfs source > code into a new repository and attempted to compile it on FreeBSD > as a kernel module: > > https://github.com/jakesfreeland/debugfs-freebsd > > Of course I was met with many, many incompatibility errors. I proceeded > to copy the required `sys/compat/linuxkpi/common/include/linux` headers > into my repository and I was met with two options: Yes, that's not going to work and isn't the right approach. > 1. continue modifying the LinuxKPI headers and commit my modifications > to src. > > 2. re-engineer the debugfs source code to comply with the preexisting > LinuxKPI headers. > > Many problems come with both approaches. First, if I modify the LinuxKPI > headers, I'd be "copying" over some code from Linux's GPLv2 headers. > I do not know how much I can "copy" before legal issues arise. Second, > if I re-engineer the debugfs source code, I am revolting against what > LinuxKPI > stands for: running Linux code with little-to-no modification. I don't know > what the correct approach is here. The purpose of the LinuxKPI is to allow Linux _drivers_ to run (mostly) unmodified on FreeBSD. Generic kernel components like debugfs itself are not meant to run under the LinuxKPI and are out of its scope. debugfs provides a set of interfaces used by drivers, including i915, to export debug info. The LinuxKPI provides a partial implementation of that interface already, in debugfs.h and lindebugfs.c, and I think the task ahead of you is to extend it to allow i915 to compile with DEBUGFS configured. (But please double check that!) > I also discovered that lindebugfs, a curtailed version of Linux's debugfs, > already exists in FreeBSD's src. I am led to believe that this is > exclusively > used under the Linuxulator so it wouldn't help me. Is this correct? No, I don't think that's accurate. It's just another pseudo filesystem, it can be used by anything that knows how to open and read files. > Thank you so much, > Jake Freeland
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?YrtwERomNF9FLEzw>