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Document LK_TRYUPGRADE.

Sponsored by:	The FreeBSD Foundation
MFC after:	3 days
Approved by:	re (marius)
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1 parent cd8e388 commit 71eaa9969e6656920856b321be3430c54dea31fc @kostikbel kostikbel committed Oct 6, 2013
Showing with 11 additions and 3 deletions.
  1. +11 −3 share/man/man9/lock.9
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14 share/man/man9/lock.9
@@ -26,7 +26,7 @@
.\"
.\" $FreeBSD$
.\"
-.Dd November 16, 2011
+.Dd October 6, 2013
.Dt LOCK 9
.Os
.Sh NAME
@@ -164,11 +164,17 @@ If an exclusive lock has been recursed, the system will
.Xr panic 9 .
.It Dv LK_UPGRADE
Upgrade a shared lock to an exclusive lock.
-If this call fails, the shared lock is lost.
+If this call fails, the shared lock is lost, even if the
+.Dv LK_NOWAIT
+flag is specified.
During the upgrade, the shared lock could
be temporarily dropped.
Attempts to upgrade an exclusive lock will cause a
.Xr panic 9 .
+.It Dv LK_TRYUPGRADE
+Try to upgrade a shared lock to an exclusive lock.
+The failure to upgrade does not result in the dropping
+of the shared lock ownership.
.It Dv LK_RELEASE
Release the lock.
Releasing a lock that is not held can cause a
@@ -333,7 +339,9 @@ fail if:
was requested and another thread had already requested a lock upgrade.
.It Bq Er EBUSY
.Dv LK_NOWAIT
-was set, and a sleep would have been required.
+was set, and a sleep would have been required, or
+.Dv LK_TRYUPGRADE
+operation was not able to upgrade the lock.
.It Bq Er ENOLCK
.Dv LK_SLEEPFAIL
was set and

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