exterror(9): dynamic kernel categories
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Authored by brooks on Tue, Jul 14, 8:08 PM.

Details

Reviewers

kib
mckusick

Summary

Make it possible to define categories without compiling their
paths into libc (important for third-party modules). A
EXTERR_CATEGORY_DYNAMIC macro can be defined to a string describing the
compilation unit (generally the path relative to src/sys) which takes
the place of EXTERR_CATEGORY.

These strings are assembled in linker sets with category numbers
assigned at system startup or module load time. The strings can be
retrieved from the kern.exterr.categories.<category> sysctl.

Diff Detail

Repository

rG FreeBSD src repository

Lint

Lint Passed

Unit

No Test Coverage

Build Status

Buildable 75040
Build 71923: arc lint + arc unit

Event Timeline

brooks created this revision.Tue, Jul 14, 8:08 PM

Herald added subscribers: ziaee, olce, imp. · View Herald TranscriptTue, Jul 14, 8:08 PM

brooks requested review of this revision.Tue, Jul 14, 8:08 PM

Harbormaster completed remote builds in B74809: Diff 181997.Tue, Jul 14, 8:08 PM

brooks added a parent revision: D58236: exterr: split category into multiple sources.Tue, Jul 14, 8:08 PM

brooks added a child revision: D58238: uexterr_gettext(3): support dynamic kernel categories.

This addresses an issue I realized during Kirk's talk at BSDCan. In the existing model, it's quite hard to support third-party modules and even in-tree modules for downstreams would require reserving a portion of the identifier space. This approach adds cost to the EXTERROR_VERBOSE reporting path, but significantly decouples the kernel and libc. I'm not sure I'd want to go as far moving entirely to dynamic, but it's probably not a problem in practice.

If I wanted to make this more efficient I'd add an AT_EXTERR_CATS and AT_EXTERR_CAT_MAX or the like and use shared pages to push out an array of pointers (or maybe with a third variable indexes) into processes addresses spaces. You might still want a fallback for categories larger than AT_EXTERR_CAT_MAX to use the sysctl interface if modules were loaded so I think this is the right direction regardless.

brooks mentioned this in D58238: uexterr_gettext(3): support dynamic kernel categories.Tue, Jul 14, 8:25 PM

brooks added inline comments.Mon, Jul 20, 10:47 AM

sys/kern/subr_exterr.c
35	This might want to be an RB tree if there are lots of modules, but this is simple

Move test here from D58238

Harbormaster completed remote builds in B75040: Diff 182526.Thu, Jul 23, 2:56 PM

kib added inline comments.Fri, Jul 24, 3:13 AM

sys/kern/subr_exterr.c
40	I think this lock can usefully be rwlock.
103	free under the mutex establishes the order between uma locks (and transitively VM locks) and the cat_mtx. Then it would be impossible to use that somewhere deep in VM. This might be not a serious issues because a loadable module probably does not provide low-level VM functionality, but there it is trivial to avoid introducing the order.