change semantics of ldisc ->compat_ioctl()

First of all, make it return int.  Returning long when native method
had never allowed that is ridiculous and inconvenient.

More importantly, change the caller; if ldisc ->compat_ioctl() is NULL
or returns -ENOIOCTLCMD, tty_compat_ioctl() will try to feed cmd and
compat_ptr(arg) to ldisc's native ->ioctl().

That simplifies ->compat_ioctl() instances quite a bit - they only
need to deal with ioctls that are neither generic tty ones (those
would get shunted off to tty_ioctl()) nor simple compat pointer ones.

Note that something like TCFLSH won't reach ->compat_ioctl(),
even if ldisc ->ioctl() does handle it - it will be recognized
earlier and passed to tty_ioctl() (and ultimately - ldisc ->ioctl()).

For many ldiscs it means that NULL ->compat_ioctl() does the
right thing.  Those where it won't serve (see e.g. n_r3964.c) are
also easily dealt with - we need to handle the numeric-argument
ioctls (calling the native instance) and, if such would exist,
the ioctls that need layout conversion, etc.

All in-tree ldiscs dealt with.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 25 insertions, 11 deletions

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 86b7e20ffd7f..6f7da9a9d76f 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2614,14 +2614,6 @@ static int gsmld_ioctl(struct tty_struct *tty, struct file *file,
 	}
 }
 
-#ifdef CONFIG_COMPAT
-static long gsmld_compat_ioctl(struct tty_struct *tty, struct file *file,
-		       unsigned int cmd, unsigned long arg)
-{
-	return gsmld_ioctl(tty, file, cmd, arg);
-}
-#endif
-
 /*
  *	Network interface
  *
@@ -2833,9 +2825,6 @@ static struct tty_ldisc_ops tty_ldisc_packet = {
 	.flush_buffer    = gsmld_flush_buffer,
 	.read            = gsmld_read,
 	.write           = gsmld_write,
-#ifdef CONFIG_COMPAT
-	.compat_ioctl    = gsmld_compat_ioctl,
-#endif
 	.ioctl           = gsmld_ioctl,
 	.poll            = gsmld_poll,
 	.receive_buf     = gsmld_receive_buf,
diff --git a/drivers/tty/n_r3964.c b/drivers/tty/n_r3964.c
index dbf1ab36758e..749a608c40b0 100644
--- a/drivers/tty/n_r3964.c
+++ b/drivers/tty/n_r3964.c
@@ -134,6 +134,10 @@ static ssize_t r3964_write(struct tty_struct *tty, struct file *file,
 		const unsigned char *buf, size_t nr);
 static int r3964_ioctl(struct tty_struct *tty, struct file *file,
 		unsigned int cmd, unsigned long arg);
+#ifdef CONFIG_COMPAT
+static int r3964_compat_ioctl(struct tty_struct *tty, struct file *file,
+		unsigned int cmd, unsigned long arg);
+#endif
 static void r3964_set_termios(struct tty_struct *tty, struct ktermios *old);
 static __poll_t r3964_poll(struct tty_struct *tty, struct file *file,
 		struct poll_table_struct *wait);
@@ -149,6 +153,9 @@ static struct tty_ldisc_ops tty_ldisc_N_R3964 = {
 	.read = r3964_read,
 	.write = r3964_write,
 	.ioctl = r3964_ioctl,
+#ifdef CONFIG_COMPAT
+	.compat_ioctl = r3964_compat_ioctl,
+#endif
 	.set_termios = r3964_set_termios,
 	.poll = r3964_poll,
 	.receive_buf = r3964_receive_buf,
@@ -1210,6 +1217,21 @@ static int r3964_ioctl(struct tty_struct *tty, struct file *file,
 	}
 }
 
+#ifdef CONFIG_COMPAT
+static int r3964_compat_ioctl(struct tty_struct *tty, struct file *file,
+		unsigned int cmd, unsigned long arg)
+{
+	switch (cmd) {
+	case R3964_ENABLE_SIGNALS:
+	case R3964_SETPRIORITY:
+	case R3964_USE_BCC:
+		return r3964_ioctl(tty, file, cmd, arg);
+	default:
+		return -ENOIOCTLCMD;
+	}
+}
+#endif
+
 static void r3964_set_termios(struct tty_struct *tty, struct ktermios *old)
 {
 	TRACE_L("set_termios");
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 1a55c3e20299..cd8df45f09d9 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2824,6 +2824,9 @@ static long tty_compat_ioctl(struct file *file, unsigned int cmd,
 		return hung_up_tty_compat_ioctl(file, cmd, arg);
 	if (ld->ops->compat_ioctl)
 		retval = ld->ops->compat_ioctl(tty, file, cmd, arg);
+	if (retval == -ENOIOCTLCMD && ld->ops->ioctl)
+		retval = ld->ops->ioctl(tty, file,
+				(unsigned long)compat_ptr(cmd), arg);
 	tty_ldisc_deref(ld);
 
 	return retval;