add new system file

hc

2024-02-20 102a0743326a03cd1a1202ceda21e175b7d3575c

 kernel/drivers/tty/tty_ioctl.c
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@@ -21,6 +21,7 @@
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 #include <linux/bitops.h>
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 #include <linux/mutex.h>
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 #include <linux/compat.h>
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+#include "tty.h"
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 #include <asm/io.h>
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 #include <linux/uaccess.h>
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@@ -397,21 +398,42 @@
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 	tmp_termios.c_ispeed = tty_termios_input_baud_rate(&tmp_termios);
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 	tmp_termios.c_ospeed = tty_termios_baud_rate(&tmp_termios);
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-	ld = tty_ldisc_ref(tty);
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+	if (opt & (TERMIOS_FLUSH|TERMIOS_WAIT)) {
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+retry_write_wait:
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+		retval = wait_event_interruptible(tty->write_wait, !tty_chars_in_buffer(tty));
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+		if (retval < 0)
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+			return retval;
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-	if (ld != NULL) {
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-		if ((opt & TERMIOS_FLUSH) && ld->ops->flush_buffer)
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-			ld->ops->flush_buffer(tty);
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-		tty_ldisc_deref(ld);
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+		if (tty_write_lock(tty, 0) < 0)
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+			goto retry_write_wait;
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+
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+		/* Racing writer? */
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+		if (tty_chars_in_buffer(tty)) {
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+			tty_write_unlock(tty);
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+			goto retry_write_wait;
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+		}
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+
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+		ld = tty_ldisc_ref(tty);
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+		if (ld != NULL) {
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+			if ((opt & TERMIOS_FLUSH) && ld->ops->flush_buffer)
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+				ld->ops->flush_buffer(tty);
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+			tty_ldisc_deref(ld);
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+		}
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+
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+		if ((opt & TERMIOS_WAIT) && tty->ops->wait_until_sent) {
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+			tty->ops->wait_until_sent(tty, 0);
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+			if (signal_pending(current)) {
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+				tty_write_unlock(tty);
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+				return -ERESTARTSYS;
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+			}
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+		}
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+
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+		tty_set_termios(tty, &tmp_termios);
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+
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+		tty_write_unlock(tty);
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+	} else {
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+		tty_set_termios(tty, &tmp_termios);
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 	}
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-
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-	if (opt & TERMIOS_WAIT) {
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-		tty_wait_until_sent(tty, 0);
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-		if (signal_pending(current))
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-			return -ERESTARTSYS;
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-	}
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-
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-	tty_set_termios(tty, &tmp_termios);
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 	/* FIXME: Arguably if tmp_termios == tty->termios AND the
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 	   actual requested termios was not tmp_termios then we may