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Modify comments regarding VOP_LOOKUP. Revised lookup description, and also 

document both cases which can set PDIRUNLOCK.

Reviewed by Bill Sommerfeld.
This commit is contained in:
wrstuden 1999-08-11 00:20:50 +00:00
parent 6be04b7f5c
commit 14693e0ca1
1 changed files with 21 additions and 8 deletions
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29
sys/kern/vnode_if.src
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@ -1,4 +1,4 @@
# $NetBSD: vnode_if.src,v 1.19 1999/08/03 18:19:08 wrstuden Exp $
# $NetBSD: vnode_if.src,v 1.20 1999/08/11 00:20:50 wrstuden Exp $
#
# Copyright (c) 1992, 1993
# The Regents of the University of California. All rights reserved.
@ -60,17 +60,30 @@
# especially that *vpp may equal dvp and both may be locked.
#
# More details:
# On success, adds a reference to *vpp so it doesn't evaporate.
# On failure, *vpp is NULL, and *dvp is left locked.
# If LOCKPARENT is set in cnp, dvp is returned locked even on success.
# otherwise it is unlocked (unless *vpp == dvp on return)
# There are three types of lookups: ".", ".." (ISDOTDOT), and other.
# On successful lookup of ".", a reference is added to dvp, and it
# is returned in *vpp.
# To look up ISDOTDOT, dvp is unlocked, the ".." node is locked, and
# then dvp is relocked iff LOCKPARENT is set and this is the last
# component name (ISLASTCN set). This preserves the
# protocol of always locking nodes from root ("/") downward and
# prevents deadlock.
# Other lookups find the named node (creating the vnode if needed) and
# return it, locked, in *vpp.
# For non-"." lookups, if LOCKPARENT is not set or this was not the
# last component name, dvp is returned unlocked on a successful
# lookup.
# On failure, *vpp is NULL, and *dvp is left locked. If there was
# an error re-locking dvp in the ISDOTDOT case, an error is
# returned with PDIRUNLOCK set.
#
# *vpp is always locked on return if the operation succeeds.
# typically, if *vpp == dvp, you need to release twice, but unlock once.
#
# If ISDOTDOT is set, dvp is unlocked before *vpp is
# locked; dvp is then relocked. this is done to avoid deadlocking
# another process concurrently scanning downwards.
# The PDIRUNLOCK flag is set when dvp is unlocked in the lookup routine.
# It signals the caller that dvp's lock state changed. It will
# be set on exit if either a successful lookup unlocked the
# parrent, or there was an error re-locking dvp in the ISDOTDOT case.
#
vop_lookup {
IN struct vnode *dvp;