Document chflagsat(2).

Obtained from:	jilles

lib/libc/sys/Makefile.inc

@@ -278,7 +278,8 @@ MLINKS+=cap_fcntls_limit.2 cap_fcntls_get.2
 MLINKS+=cap_ioctls_limit.2 cap_ioctls_get.2
 MLINKS+=cap_rights_limit.2 cap_rights_get.2
 MLINKS+=chdir.2 fchdir.2
-MLINKS+=chflags.2 fchflags.2 \
+MLINKS+=chflags.2 chflagsat.2 \
+	chflags.2 fchflags.2 \
 	chflags.2 lchflags.2
 MLINKS+=chmod.2 fchmod.2 \
 	chmod.2 fchmodat.2 \

lib/libc/sys/cap_rights_limit.2

@@ -159,7 +159,12 @@ Permit
 .Xr fchdir 2 .
 .It Dv CAP_FCHFLAGS
 Permit
-.Xr fchflags 2 .
+.Xr fchflags 2
+and
+.Xr chflagsat 2 .
+.It Dv CAP_CHFLAGSAT
+An alias to
+.Dv CAP_FCHFLAGS .
 .It Dv CAP_FCHMOD
 Permit
 .Xr fchmod 2

lib/libc/sys/chflags.2

@@ -28,7 +28,7 @@
 .\"	@(#)chflags.2	8.3 (Berkeley) 5/2/95
 .\" $FreeBSD$
 .\"
-.Dd Apr 13, 2012
+.Dd March 22, 2013
 .Dt CHFLAGS 2
 .Os
 .Sh NAME
@@ -47,6 +47,8 @@
 .Fn lchflags "const char *path" "unsigned long flags"
 .Ft int
 .Fn fchflags "int fd" "unsigned long flags"
+.Ft int
+.Fn chflagsat "int fd" "const char *path" "unsigned long flags" "int atflag"
 .Sh DESCRIPTION
 The file whose name
 is given by
@@ -66,6 +68,45 @@ in which case
 will change the flags of the link itself,
 rather than the file it points to.
 .Pp
+The
+.Fn chflagsat
+is equivalent to either
+.Fn chflags
+or
+.Fn lchflags
+depending on the
+.Fa atflag
+except in the case where
+.Fa path
+specifies a relative path.
+In this case the file to be changed is determined relative to the directory
+associated with the file descriptor
+.Fa fd
+instead of the current working directory.
+The values for the
+.Fa atflag
+are constructed by a bitwise-inclusive OR of flags from the following list,
+defined in
+.In fcntl.h :
+.Bl -tag -width indent
+.It Dv AT_SYMLINK_NOFOLLOW
+If
+.Fa path
+names a symbolic link, then the flags of the symbolic link are changed.
+.El
+.Pp
+If
+.Fn chflagsat
+is passed the special value
+.Dv AT_FDCWD
+in the
+.Fa fd
+parameter, the current working directory is used.
+If also
+.Fa atflag
+is zero, the behavior is identical to a call to
+.Fn chflags .
+.Pp
 The flags specified are formed by
 .Em or Ns 'ing
 the following values
@@ -236,3 +277,7 @@ The
 .Fn lchflags
 system call first appeared in
 .Fx 5.0 .
+The
+.Fn chflagsat
+system call first appeared in
+.Fx 10.0 .