Add a new 'void closefrom(int lowfd)' system call. When called, it closes

any open file descriptors >= 'lowfd'.  It is largely identical to the same
function on other operating systems such as Solaris, DFly, NetBSD, and
OpenBSD.  One difference from other *BSD is that this closefrom() does not
fail with any errors.  In practice, while the manpages for NetBSD and
OpenBSD claim that they return EINTR, they ignore internal errors from
close() and never return EINTR.  DFly does return EINTR, but for the common
use case (closing fd's prior to execve()), the caller really wants all
fd's closed and returning EINTR just forces callers to call closefrom() in
a loop until it stops failing.

Note that this implementation of closefrom(2) does not make any effort to
resolve userland races with open(2) in other threads.  As such, it is not
multithread safe.

Submitted by:	rwatson (initial version)
Reviewed by:	rwatson
MFC after:	2 weeks

4 files changed, 58 insertions, 1 deletions

diff --git a/lib/libc/sys/Makefile.inc b/lib/libc/sys/Makefile.inc
index a238efc..7e65aa4 100644
--- a/lib/libc/sys/Makefile.inc
+++ b/lib/libc/sys/Makefile.inc
@@ -63,7 +63,7 @@ MAN+=	abort2.2 accept.2 access.2 acct.2 adjtime.2 \
 	aio_cancel.2 aio_error.2 aio_read.2 aio_return.2 \
 	aio_suspend.2 aio_waitcomplete.2 aio_write.2 \
 	bind.2 brk.2 chdir.2 chflags.2 \
-	chmod.2 chown.2 chroot.2 clock_gettime.2 close.2 \
+	chmod.2 chown.2 chroot.2 clock_gettime.2 close.2 closefrom.2 \
 	connect.2 cpuset.2 cpuset_getaffinity.2 dup.2 execve.2 _exit.2 \
 	extattr_get_file.2 fcntl.2 fhopen.2 flock.2 fork.2 fsync.2 \
 	getdirentries.2 getdtablesize.2 \
diff --git a/lib/libc/sys/Symbol.map b/lib/libc/sys/Symbol.map
index 48ef400..9e19899 100644
--- a/lib/libc/sys/Symbol.map
+++ b/lib/libc/sys/Symbol.map
@@ -333,6 +333,7 @@ FBSD_1.0 {
 };
 
 FBSD_1.1 {
+	closefrom;
 	cpuset;
 	cpuset_getid;
 	cpuset_setid;
@@ -472,6 +473,8 @@ FBSDprivate_1.0 {
 	__sys_clock_settime;
 	_close;
 	__sys_close;
+	_closefrom;
+	__sys_closefrom;
 	_connect;
 	__sys_connect;
 	_cpuset;
diff --git a/lib/libc/sys/close.2 b/lib/libc/sys/close.2
index aef0379..524322b 100644
--- a/lib/libc/sys/close.2
+++ b/lib/libc/sys/close.2
@@ -120,6 +120,7 @@ before all pending data was delivered.
 .El
 .Sh SEE ALSO
 .Xr accept 2 ,
+.Xr closefrom 2 ,
 .Xr execve 2 ,
 .Xr fcntl 2 ,
 .Xr flock 2 ,
diff --git a/lib/libc/sys/closefrom.2 b/lib/libc/sys/closefrom.2
new file mode 100644
index 0000000..ffaa001
--- /dev/null
+++ b/lib/libc/sys/closefrom.2
@@ -0,0 +1,53 @@
+.\" Copyright (c) 2009 Advanced Computing Technologies LLC
+.\" Written by: John H. Baldwin <jhb@FreeBSD.org>
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd June 12, 2009
+.Dt CLOSEFROM 2
+.Os
+.Sh NAME
+.Nm closefrom
+.Nd delete open file descriptors
+.Sh LIBRARY
+.Lb libc
+.Sh SYNOPSIS
+.In unistd.h
+.Ft void
+.Fn closefrom "int lowfd"
+.Sh DESCRIPTION
+The
+.Fn closefrom
+system call deletes all open file descriptors greater than or equal to
+.Fa lowfd
+from the per-process object reference table.
+Any errors encountered while closing file descriptors are ignored.
+.Sh SEE ALSO
+.Xr close 2
+.Sh HISTORY
+The
+.Fn closefrom
+function first appeared in
+.Fx 8.0 .