Extend the kernel unit number allocator for allocating specific unit

numbers. This change adds a new function alloc_unr_specific() which
returns the requested unit number if it is free. If the number is
already allocated or out of the range, -1 is returned.

Update alloc_unr(9) manual page accordingly and add a MLINK for
alloc_unr_specific(9).

Discussed on:	freebsd-hackers

2 files changed, 12 insertions, 1 deletions

diff --git a/share/man/man9/Makefile b/share/man/man9/Makefile
index 4e8b0cedd6f4..6e932443f031 100644
--- a/share/man/man9/Makefile
+++ b/share/man/man9/Makefile
@@ -374,6 +374,7 @@ MAN=	accept_filter.9 \
 	zone.9
 
 MLINKS=	alloc_unr.9 alloc_unrl.9 \
+	alloc_unr.9 alloc_unr_specific.9 \
 	alloc_unr.9 delete_unrhdr.9 \
 	alloc_unr.9 free_unr.9 \
 	alloc_unr.9 new_unrhdr.9
diff --git a/share/man/man9/alloc_unr.9 b/share/man/man9/alloc_unr.9
index 2ba93e6f984e..43c145f5c7a3 100644
--- a/share/man/man9/alloc_unr.9
+++ b/share/man/man9/alloc_unr.9
@@ -24,13 +24,14 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd February 7, 2010
+.Dd July 5, 2010
 .Dt ALLOC_UNR 9
 .Os
 .Sh NAME
 .Nm new_unrhdr ,
 .Nm delete_unrhdr ,
 .Nm alloc_unr ,
+.Nm alloc_unr_specific ,
 .Nm free_unr
 .Nd "kernel unit number allocator"
 .Sh SYNOPSIS
@@ -43,6 +44,8 @@
 .Fn alloc_unr "struct unrhdr *uh"
 .Ft int
 .Fn alloc_unrl "struct unrhdr *uh"
+.Ft int
+.Fn alloc_unr_specific "struct unrhdr *uh" "u_int item"
 .Ft void
 .Fn free_unr "struct unrhdr *uh" "u_int item"
 .Sh DESCRIPTION
@@ -81,6 +84,13 @@ is returned.
 Same as
 .Fn alloc_unr
 except that mutex is assumed to be already locked and thus is not used.
+.It Fn alloc_unr_specific uh item
+Allocate a specific unit number.
+This function allocates memory and thus may sleep.
+The allocated unit number is returned on success.
+If the specified number is already allocated or out of the range,
+.Li \-1
+is returned.
 .It Fn free_unr uh item
 Free a previously allocated unit number.
 This function may require allocating memory, and thus it can sleep.