p9fs: implement basic pathconf support
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Authored by arichardson on Sat, Apr 18, 5:56 AM.

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Reviewers

markj
kib

Group Reviewers

cheri

Summary

This is needed for various pjdfstest tests which fail with syntax errors
if pathconf _PC_NAME_MAX/_PC_PATH_MAX return -1. For NAME_MAX we can use
the 9P2000.L Tstatfs call to get namelen from the host. While this could
theoretically be different for nested filesystems in the shared mount it
is a much better guess than just returning 255.
There does not seem to be a way to get the host PATH_MAX, so we just
return the conservative kernel default.

Found while fixing https://github.com/CTSRD-CHERI/cheribsd/issues/2617.

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Repository

rG FreeBSD src repository

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No Test Coverage

Build Status

Buildable 72314
Build 69197: arc lint + arc unit

Event Timeline

arichardson created this revision.Sat, Apr 18, 5:56 AM

Herald added a subscriber: imp. · View Herald TranscriptSat, Apr 18, 5:56 AM

arichardson requested review of this revision.Sat, Apr 18, 5:56 AM

Herald added a reviewer: cheri. · View Herald TranscriptSat, Apr 18, 5:56 AM

Harbormaster completed remote builds in B72314: Diff 175816.Sat, Apr 18, 5:56 AM

arichardson added a parent revision: D56492: p9fs: Move UMA zone initialization to VFS module lifecycle.Sat, Apr 18, 6:01 AM

kib added inline comments.Sat, Apr 18, 7:56 PM

sys/fs/p9fs/p9fs_vnops.c
2286	Should we use cmpset there, or even something similar to compare-and-set-if_greater?

arichardson added inline comments.Sun, Apr 19, 1:21 AM

sys/fs/p9fs/p9fs_vnops.c
2286	We could do, but I think it's not worth it: if we end up racing and having multiple assignments those will always be the same unless we have nested mounts inside the p9fs. And if we have nested mounts (which we can't know inside the guest) there isn't a single correct value, so any of the values should be acceptable.