termios: New ioctl: TIOCOUTQ

Change-Id: I86f2a7b007137e22cf7d6fc8ad6675ff5de267d4
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6386
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Jessica Hamilton <jessica.l.hamilton@gmail.com>

headers/posix/termios.h

@@ -188,6 +188,7 @@ struct termios {
 #define TIOCMBIS			(TCGETA + 22)	/* set bits in line state */
 #define TIOCMBIC			(TCGETA + 23)	/* clear bits in line state */
 #define	TIOCGSID			(TCGETA + 24)	/* get session leader process group ID */
+#define TIOCOUTQ			(TCGETA + 25)	/* get output queue size */
 
 /* Event codes.  Returned from TCWAITEVENT */
 #define EV_RING			0x0001

src/add-ons/kernel/generic/tty/tty.cpp

@@ -1830,6 +1830,26 @@ tty_control(tty_cookie* cookie, uint32 op, void* buffer, size_t length)
 			return B_OK;
 		}
 
+		case TIOCOUTQ:
+		{
+			int toWrite = 0;
+
+			// release the mutex and grab a write lock
+			locker.Unlock();
+			WriterLocker writeLocker(cookie);
+
+			status_t status = writeLocker.AcquireWriter(0, 1);
+			if (status == B_OK)
+				toWrite = line_buffer_readable(tty->input_buffer);
+			else if (status != B_WOULD_BLOCK)
+				return status;
+
+			if (user_memcpy(buffer, &toWrite, sizeof(int)) != B_OK)
+				return B_BAD_ADDRESS;
+
+			return B_OK;
+		}
+
 		case TCXONC:			// Unix, but even Linux doesn't handle it
 			//dprintf("tty: unsupported TCXONC\n");
 			break;

src/bin/debug/strace/ioctl.cpp

@@ -136,6 +136,7 @@ static const ioctl_info kIOCtls[] = {
 	IOCTL_INFO_ENTRY(TIOCCBRK),
 	IOCTL_INFO_ENTRY(TIOCMBIS),
 	IOCTL_INFO_ENTRY(TIOCMBIC),
+	IOCTL_INFO_ENTRY(TIOCOUTQ),
 	// private termios
 	IOCTL_INFO_ENTRY(B_IOCTL_GET_TTY_INDEX),
 	IOCTL_INFO_ENTRY(B_IOCTL_GRANT_TTY),