Messages in this thread Patch in this message | | | From | Walt Drummond <> | Subject | [PATCH 1/3] vstatus: Allow the n_tty line dicipline to write to a user tty | Date | Mon, 17 Jan 2022 20:43:21 -0800 |
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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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