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Subject[PATCH 1/3] vstatus: Allow the n_tty line dicipline to write to a user tty
Date
Refactor the implementation of n_tty_write() into do_n_tty_write(), and
change n_tty_write() to call do_n_tty_write() after acquiring
tty.termios_rwsem.

This allows the n_tty line dicipline to write to a user tty via
do_n_tty_write() when already holding tty.termios_rwsem.

Signed-off-by: Walt Drummond <walt@drummond.us>
---
drivers/tty/n_tty.c | 76 ++++++++++++++++++++++++++-------------------
1 file changed, 44 insertions(+), 32 deletions(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 5be6d02dc690..6a6e7da80095 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -2231,29 +2231,7 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
return retval;
}

-/**
- * n_tty_write - write function for tty
- * @tty: tty device
- * @file: file object
- * @buf: userspace buffer pointer
- * @nr: size of I/O
- *
- * Write function of the terminal device. This is serialized with
- * respect to other write callers but not to termios changes, reads
- * and other such events. Since the receive code will echo characters,
- * thus calling driver write methods, the output_lock is used in
- * the output processing functions called here as well as in the
- * echo processing function to protect the column state and space
- * left in the buffer.
- *
- * This code must be sure never to sleep through a hangup.
- *
- * Locking: output_lock to protect column state and space left
- * (note that the process_output*() functions take this
- * lock themselves)
- */
-
-static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
+static ssize_t do_n_tty_write(struct tty_struct *tty, struct file *file,
const unsigned char *buf, size_t nr)
{
const unsigned char *b = buf;
@@ -2261,14 +2239,7 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
int c;
ssize_t retval = 0;

- /* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
- if (L_TOSTOP(tty) && file->f_op->write_iter != redirected_tty_write) {
- retval = tty_check_change(tty);
- if (retval)
- return retval;
- }
-
- down_read(&tty->termios_rwsem);
+ lockdep_assert_held_read(&tty->termios_rwsem);

/* Write out any echoed characters that are still pending */
process_echoes(tty);
@@ -2336,10 +2307,51 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
remove_wait_queue(&tty->write_wait, &wait);
if (nr && tty->fasync)
set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
- up_read(&tty->termios_rwsem);
+
return (b - buf) ? b - buf : retval;
}

+/**
+ * n_tty_write - write function for tty
+ * @tty: tty device
+ * @file: file object
+ * @buf: userspace buffer pointer
+ * @nr: size of I/O
+ *
+ * Write function of the terminal device. This is serialized with
+ * respect to other write callers but not to termios changes, reads
+ * and other such events. Since the receive code will echo characters,
+ * thus calling driver write methods, the output_lock is used in
+ * the output processing functions called here as well as in the
+ * echo processing function to protect the column state and space
+ * left in the buffer.
+ *
+ * This code must be sure never to sleep through a hangup.
+ *
+ * Locking: output_lock to protect column state and space left
+ * (note that the process_output*() functions take this
+ * lock themselves)
+ */
+
+static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
+ const unsigned char *buf, size_t nr)
+{
+ ssize_t retval = 0;
+
+ /* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
+ if (L_TOSTOP(tty) && file->f_op->write_iter != redirected_tty_write) {
+ retval = tty_check_change(tty);
+ if (retval)
+ return retval;
+ }
+
+ down_read(&tty->termios_rwsem);
+ retval = do_n_tty_write(tty, file, buf, nr);
+ up_read(&tty->termios_rwsem);
+
+ return retval;
+}
+
/**
* n_tty_poll - poll method for N_TTY
* @tty: terminal device
--
2.30.2
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