[PATCH v2] improve error handling of ttyname_r and isatty

[Benjamin Peterson <benjamin@python.org>]

POSIX allows ttyname(_r) and isatty to return EBADF if passed file descriptor is
invalid.
---
 src/unistd/isatty.c    | 6 +++++-
 src/unistd/ttyname_r.c | 2 +-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/unistd/isatty.c b/src/unistd/isatty.c
index c8badaf5..75a9c186 100644
--- a/src/unistd/isatty.c
+++ b/src/unistd/isatty.c
@@ -1,9 +1,13 @@
 #include <unistd.h>
+#include <errno.h>
 #include <sys/ioctl.h>
 #include "syscall.h"
 
 int isatty(int fd)
 {
 	struct winsize wsz;
-	return !__syscall(SYS_ioctl, fd, TIOCGWINSZ, &wsz);
+	unsigned long r = syscall(SYS_ioctl, fd, TIOCGWINSZ, &wsz);
+	if (r == 0) return 1;
+	if (errno != EBADF) errno = ENOTTY;
+	return 0;
 }
diff --git a/src/unistd/ttyname_r.c b/src/unistd/ttyname_r.c
index 33aa4ae1..24106ad8 100644
--- a/src/unistd/ttyname_r.c
+++ b/src/unistd/ttyname_r.c
@@ -10,7 +10,7 @@ int ttyname_r(int fd, char *name, size_t size)
 	char procname[sizeof "/proc/self/fd/" + 3*sizeof(int) + 2];
 	ssize_t l;
 
-	if (!isatty(fd)) return ENOTTY;
+	if (!isatty(fd)) return errno;
 
 	__procfdname(procname, fd);
 	l = readlink(procname, name, size);
-- 
2.17.1