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Differential D21015

sbuf(9): Add NOWAIT dynamic buffer extension mode
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Authored by cem on Jul 21 2019, 5:17 PM.

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vangyzen
bapt

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rG819999651131: sbuf(9): Add NOWAIT dynamic buffer extension mode
rS350691: sbuf(9): Add NOWAIT dynamic buffer extension mode

Summary

The goal is to avoid some kinds of low-memory deadlock when formatting
buffers.

Test Plan

This reconciles one of the few semantic gaps between our in-house sbuf clone
and sbuf(9).

Diff Detail

Repository

rS FreeBSD src repository - subversion

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Unit

Tests Not Applicable

Event Timeline

cem created this revision.Jul 21 2019, 5:17 PM

Harbormaster completed remote builds in B25444: Diff 59991.Jul 21 2019, 5:18 PM

Need to M_NOWAIT the allocation in sbuf_newbuf for this use case as well.

Harbormaster completed remote builds in B25445: Diff 59992.Jul 21 2019, 6:25 PM

vangyzen added inline comments.Jul 21 2019, 8:28 PM

share/man/man9/sbuf.9
46 ↗	(On Diff #59992)	Oops.
sys/kern/subr_sbuf.c
240 ↗	(On Diff #59992)	Why do we ignore `SBUF_NOWAIT` in `flags` here? (Was this just for testing?)

Thanks!

share/man/man9/sbuf.9
46 ↗	(On Diff #59992)	vim-o, will fix
sys/kern/subr_sbuf.c
240 ↗	(On Diff #59992)	This one is actually constructing the `struct sbuf` itself. I don't see much value in a heap version of that one that gracefully handles OOM, but I don't feel strongly about it. If you'd prefer it for consistency, I'm happy to use the flag here as well.

Fix the typo in sbuf.9

Harbormaster completed remote builds in B25448: Diff 60002.Jul 22 2019, 12:09 AM

vangyzen added inline comments.Jul 22 2019, 12:32 AM

sys/kern/subr_sbuf.c
240 ↗	(On Diff #59992)	I agree that it doesn’t seem useful, but I think it’s best to be consistent. If the caller passes NOWAIT, blocking in malloc would be astonishing behavior.

Extend use of NOWAIT flag to initial heap sbuf allocation.

Harbormaster completed remote builds in B25449: Diff 60003.Jul 22 2019, 1:34 AM

vangyzen accepted this revision.Jul 22 2019, 1:41 AM

This revision is now accepted and ready to land.Jul 22 2019, 1:41 AM

cem added a child revision: D21029: sbuf(9): Refactor sbuf_newbuf into sbuf_new.Jul 22 2019, 4:54 PM

Closed by commit rS350691: sbuf(9): Add NOWAIT dynamic buffer extension mode (authored by cem). · Explain WhyAug 7 2019, 7:23 PM

This revision was automatically updated to reflect the committed changes.

cem added a commit: rS350691: sbuf(9): Add NOWAIT dynamic buffer extension mode.

Herald added a reviewer: manpages. · View Herald TranscriptAug 7 2019, 7:23 PM

Herald added a subscriber: imp. · View Herald Transcript

imp added a commit: rG819999651131: sbuf(9): Add NOWAIT dynamic buffer extension mode.Jul 16 2021, 5:47 PM

Revision Contents
Changeset List

Path

Size

head/

share/

man/

man9/

7 lines

sys/

kern/

16 lines

sys/

1 line

Diff 60552

head/share/man/man9/sbuf.9

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head/sys/kern/subr_sbuf.c

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head/sys/sys/sbuf.h

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