Add two new routines: fdevname() and fdevname_r().

A more elegant way of obtaining a name of a character device by its file
descriptor on FreeBSD, is to use the FIODGNAME ioctl. Because a valid
file descriptor implies a file descriptor is visible in /dev, it will
always resolve a valid device name.

I'm adding a more friendly wrapper for this ioctl, called fdevname(). It
is a lot easier to use than devname() and also has better error
handling. When a device name cannot be resolved, it will just return
NULL instead of a generated device name that makes no sense.

Discussed with:	kib

1 files changed, 2 insertions, 12 deletions

diff --git a/lib/libc/gen/ttyname.c b/lib/libc/gen/ttyname.c
index 6543604..a21b77f 100644
--- a/lib/libc/gen/ttyname.c
+++ b/lib/libc/gen/ttyname.c
@@ -35,7 +35,6 @@ __FBSDID("$FreeBSD$");
 
 #include "namespace.h"
 #include <sys/types.h>
-#include <sys/stat.h>
 #include <sys/ioctl.h>
 #include <sys/filio.h>
 #include <fcntl.h>
@@ -60,8 +59,6 @@ static int		ttyname_keycreated = 0;
 int
 ttyname_r(int fd, char *buf, size_t len)
 {
-	struct stat	sb;
-	struct fiodgname_arg fgn;
 	size_t used;
 
 	*buf = '\0';
@@ -69,21 +66,14 @@ ttyname_r(int fd, char *buf, size_t len)
 	/* Must be a terminal. */
 	if (!isatty(fd))
 		return (ENOTTY);
-	/* Must be a character device. */
-	if (_fstat(fd, &sb) || !S_ISCHR(sb.st_mode))
-		return (ENOTTY);
 	/* Must have enough room */
 	if (len <= sizeof(_PATH_DEV))
 		return (ERANGE);
 
 	strcpy(buf, _PATH_DEV);
 	used = strlen(buf);
-	fgn.len = len - used;
-	fgn.buf = buf + used;
-	if (!_ioctl(fd, FIODGNAME, &fgn))
-		return (0);
-	used = strlen(buf);
-	devname_r(sb.st_rdev, S_IFCHR, buf + used, len - used);
+	if (fdevname_r(fd, buf + used, len - used) == NULL)
+		return (ENOTTY);
 	return (0);
 }