ctermid(3): Fix return values section

ctermid() doesn't, and has never, set errno.

While here, add ctermid_r to the name section and align the parameter
name in the source file.

Reviewed by:	bnovkov
Approved by:	bnovkov
MFC after:	3 days
Obtained from:	https://github.com/apple-oss-distributions/libc
Sponsored by:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D57396

2 files changed, 22 insertions, 17 deletions

diff --git a/lib/libc/gen/ctermid.3 b/lib/libc/gen/ctermid.3
index 2a53412f1b29..daf59f32c157 100644
--- a/lib/libc/gen/ctermid.3
+++ b/lib/libc/gen/ctermid.3
@@ -25,11 +25,12 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd October 1, 2011
+.Dd June 2, 2026
 .Dt CTERMID 3
 .Os
 .Sh NAME
-.Nm ctermid
+.Nm ctermid ,
+.Nm ctermid_r
 .Nd generate terminal pathname
 .Sh LIBRARY
 .Lb libc
@@ -78,14 +79,18 @@ If no suitable lookup of the controlling terminal name can be performed,
 this implementation returns
 .Ql /dev/tty .
 .Sh RETURN VALUES
-Upon successful completion, a
-.Pf non- Dv NULL
-pointer is returned.
-Otherwise, a
-.Dv NULL
-pointer is returned and the global variable
-.Va errno
-is set to indicate the error.
+The
+.Fn ctermid
+function returns
+.Fa buf
+if it is
+.Pf non- Dv NULL ,
+otherwise it returns the address of a static buffer.
+The
+.Fn ctermid_r
+function always returns
+.Fa buf ,
+even if it is the NULL pointer.
 .Sh ERRORS
 The current implementation detects no error conditions.
 .Sh SEE ALSO
diff --git a/lib/libc/gen/ctermid.c b/lib/libc/gen/ctermid.c
index fb117b3c8ded..1ca2401f0c1d 100644
--- a/lib/libc/gen/ctermid.c
+++ b/lib/libc/gen/ctermid.c
@@ -39,32 +39,32 @@
 #define	LEN_PATH_DEV	(sizeof(_PATH_DEV) - 1)
 
 char *
-__ssp_real(ctermid)(char *s)
+__ssp_real(ctermid)(char *buf)
 {
 	static char def[sizeof(_PATH_DEV) + SPECNAMELEN];
 	struct stat sb;
 	size_t dlen;
 	int sverrno;
 
-	if (s == NULL) {
-		s = def;
+	if (buf == NULL) {
+		buf = def;
 		dlen = sizeof(def) - LEN_PATH_DEV;
 	} else
 		dlen = L_ctermid - LEN_PATH_DEV;
-	strcpy(s, _PATH_TTY);
+	strcpy(buf, _PATH_TTY);
 
 	/* Attempt to perform a lookup of the actual TTY pathname. */
 	sverrno = errno;
 	if (stat(_PATH_TTY, &sb) == 0 && S_ISCHR(sb.st_mode))
-		(void)sysctlbyname("kern.devname", s + LEN_PATH_DEV,
+		(void)sysctlbyname("kern.devname", buf + LEN_PATH_DEV,
 		    &dlen, &sb.st_rdev, sizeof(sb.st_rdev));
 	errno = sverrno;
 	return (s);
 }
 
 char *
-__ssp_real(ctermid_r)(char *s)
+__ssp_real(ctermid_r)(char *buf)
 {
 
-	return (s != NULL ? ctermid(s) : NULL);
+	return (buf != NULL ? ctermid(buf) : NULL);
 }