libc: Allow setting close-on-exec in fopen/freopen/fdopen.

This commit adds a new mode option 'e' that must follow any 'b', '+' and/or
'x' options. C11 is clear about the 'x' needing to follow 'b' and/or '+' and
that is what we implement; therefore, require a strict position for 'e' as
well.

For freopen() with a non-NULL path argument and fopen(), the close-on-exec
flag is set iff the 'e' mode option is specified. For freopen() with a NULL
path argument and fdopen(), the close-on-exec flag is turned on if the 'e'
mode option is specified and remains unchanged otherwise.

Although the same behaviour for fopen() can be obtained by open(O_CLOEXEC)
and fdopen(), this needlessly complicates the calling code.

Apart from the ordering requirement, the new option matches glibc.

PR:		kern/169320

1 files changed, 18 insertions, 1 deletions

diff --git a/lib/libc/stdio/fopen.3 b/lib/libc/stdio/fopen.3
index 08438e7..da89ed4 100644
--- a/lib/libc/stdio/fopen.3
+++ b/lib/libc/stdio/fopen.3
@@ -32,7 +32,7 @@
 .\"     @(#)fopen.3	8.1 (Berkeley) 6/4/93
 .\" $FreeBSD$
 .\"
-.Dd October 17, 2011
+.Dd November 30, 2012
 .Dt FOPEN 3
 .Os
 .Sh NAME
@@ -97,6 +97,14 @@ or
 causes the
 .Fn fopen
 call to fail if the file already exists.
+An optional
+.Dq Li e
+following the above
+causes the
+.Fn fopen
+call to set the
+.Dv FD_CLOEXEC
+flag on the underlying file descriptor.
 .Pp
 The
 .Fa mode
@@ -144,6 +152,11 @@ of the stream must be compatible with the mode of the file descriptor.
 The
 .Dq Li x
 mode option is ignored.
+If the
+.Dq Li e
+mode option is present, the
+.Dv FD_CLOEXEC
+flag is set, otherwise it remains unchanged.
 When the stream is closed via
 .Xr fclose 3 ,
 .Fa fildes
@@ -277,3 +290,7 @@ The
 function
 conforms to
 .St -p1003.1-88 .
+The
+.Dq Li e
+mode option does not conform to any standard
+but is also supported by glibc.