There is an optimization in chmod(1), that makes it not to call chmod(2)

if the new file mode is the same as it was before; however, this
optimization must be disabled for filesystems that support NFSv4 ACLs.
Chmod uses pathconf(2) to determine whether this is the case - however,
pathconf(2) always follows symbolic links, while the 'chmod -h' doesn't.

This change adds lpathconf(3) to make it possible to solve that problem
in a clean way.

Reviewed by:	rwatson (earlier version)
Approved by:	re (kib)

3 files changed, 27 insertions, 3 deletions

diff --git a/lib/libc/sys/Makefile.inc b/lib/libc/sys/Makefile.inc
index ad6b06e..da4f3c5 100644
--- a/lib/libc/sys/Makefile.inc
+++ b/lib/libc/sys/Makefile.inc
@@ -159,6 +159,7 @@ MLINKS+=mq_send.2 mq_timedsend.2
 MLINKS+=ntp_adjtime.2 ntp_gettime.2
 MLINKS+=open.2 openat.2
 MLINKS+=pathconf.2 fpathconf.2
+MLINKS+=pathconf.2 lpathconf.2
 MLINKS+=read.2 pread.2 read.2 preadv.2 read.2 readv.2
 MLINKS+=readlink.2 readlinkat.2
 MLINKS+=recv.2 recvfrom.2 recv.2 recvmsg.2
diff --git a/lib/libc/sys/Symbol.map b/lib/libc/sys/Symbol.map
index 88bc779..901b261 100644
--- a/lib/libc/sys/Symbol.map
+++ b/lib/libc/sys/Symbol.map
@@ -346,6 +346,7 @@ FBSD_1.1 {
 	jail_set;
 	jail_remove;
 	linkat;
+	lpathconf;
 	mkdirat;
 	mkfifoat;
 	mknodat;
diff --git a/lib/libc/sys/pathconf.2 b/lib/libc/sys/pathconf.2
index daf95ab..495bc65 100644
--- a/lib/libc/sys/pathconf.2
+++ b/lib/libc/sys/pathconf.2
@@ -28,11 +28,12 @@
 .\"	@(#)pathconf.2	8.1 (Berkeley) 6/4/93
 .\" $FreeBSD$
 .\"
-.Dd June 25, 2009
+.Dd July 7, 2009
 .Dt PATHCONF 2
 .Os
 .Sh NAME
 .Nm pathconf ,
+.Nm lpathconf ,
 .Nm fpathconf
 .Nd get configurable pathname variables
 .Sh LIBRARY
@@ -42,10 +43,13 @@
 .Ft long
 .Fn pathconf "const char *path" "int name"
 .Ft long
+.Fn lpathconf "const char *path" "int name"
+.Ft long
 .Fn fpathconf "int fd" "int name"
 .Sh DESCRIPTION
 The
-.Fn pathconf
+.Fn pathconf ,
+.Fn lpathconf
 and
 .Fn fpathconf
 system calls provide a method for applications to determine the current
@@ -53,7 +57,9 @@ value of a configurable system limit or option variable associated
 with a pathname or file descriptor.
 .Pp
 For
-.Fn pathconf ,
+.Fn pathconf
+and
+.Fn lpathconf ,
 the
 .Fa path
 argument is the name of a file or directory.
@@ -68,6 +74,18 @@ argument specifies the system variable to be queried.
 Symbolic constants for each name value are found in the include file
 .Li <unistd.h> .
 .Pp
+The
+.Fn lpathconf
+system call is like
+.Fn pathconf
+except in the case where the named file is a symbolic link,
+in which case
+.Fn lpathconf
+returns information about the link,
+while
+.Fn pathconf
+returns information about the file the link references.
+.Pp
 The available values are as follows:
 .Pp
 .Bl -tag -width 6n
@@ -239,3 +257,7 @@ and
 .Fn fpathconf
 system calls first appeared in
 .Bx 4.4 .
+The
+.Fn lpathconf
+system call first appeared in
+.Fx 8.0 .