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, 5 insertions, 0 deletions

diff --git a/lib/libc/stdio/flags.c b/lib/libc/stdio/flags.c
index 0b6b075..e445fed 100644
--- a/lib/libc/stdio/flags.c
+++ b/lib/libc/stdio/flags.c
@@ -97,6 +97,7 @@ __sflags(mode, optr)
 
 	/* 'x' means exclusive (fail if the file exists) */
 	if (*mode == 'x') {
+		mode++;
 		if (m == O_RDONLY) {
 			errno = EINVAL;
 			return (0);
@@ -104,6 +105,10 @@ __sflags(mode, optr)
 		o |= O_EXCL;
 	}
 
+	/* set close-on-exec */
+	if (*mode == 'e')
+		o |= O_CLOEXEC;
+
 	*optr = m | o;
 	return (ret);
 }