From ed3f0af8c0b7e161efc5ba7228ca4cbd747c903d Mon Sep 17 00:00:00 2001 From: Alan Cox Date: Mon, 16 Jan 2017 16:54:29 -0600 Subject: [PATCH] tty_port: allow a port to be opened with a tty that has no file handle Let us create tty objects entirely in kernel space. Untested proposal to show why all the ideas around rewriting half the uart stack are not needed. With this a kernel created non file backed tty object could be used to handle data, and set terminal modes. Not all ldiscs can cope with this as N_TTY in particular has to work back to the fs/tty layer. The tty_port code is however otherwise clean of file handles as far as I can tell as is the low level tty port write path used by the ldisc, the configuration low level interfaces and most of the ldiscs. Currently you don't have any exposure to see tty hangups because those are built around the file layer. However a) it's a fixed port so you probably don't care about that b) if you do we can add a callback and c) you almost certainly don't want the userspace tear down/rebuild behaviour anyway. This should however be sufficient if we wanted for example to enumerate all the bluetooth bound fixed ports via ACPI and make them directly available. It doesn't deal with the case of a user opening a port that's also kernel opened and that would need some locking out (so it returned EBUSY if bound to a kernel device of some kind). That needs resolving along with how you "up" or "down" your new bluetooth device, or enumerate it while providing the existing tty API to avoid regressions (and to debug). Signed-off-by: Alan Cox Reviewed-by: Andy Shevchenko Reviewed-By: Sebastian Reichel Signed-off-by: Rob Herring Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_io.c | 2 +- drivers/tty/tty_port.c | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index 4790c0fb5a45..a1fd3f7d487a 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -855,7 +855,7 @@ static void tty_vhangup_session(struct tty_struct *tty) int tty_hung_up_p(struct file *filp) { - return (filp->f_op == &hung_up_tty_fops); + return (filp && filp->f_op == &hung_up_tty_fops); } EXPORT_SYMBOL(tty_hung_up_p); diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c index c3f9d93ba227..606d9e5bf28f 100644 --- a/drivers/tty/tty_port.c +++ b/drivers/tty/tty_port.c @@ -335,7 +335,7 @@ EXPORT_SYMBOL(tty_port_lower_dtr_rts); * tty_port_block_til_ready - Waiting logic for tty open * @port: the tty port being opened * @tty: the tty device being bound - * @filp: the file pointer of the opener + * @filp: the file pointer of the opener or NULL * * Implement the core POSIX/SuS tty behaviour when opening a tty device. * Handles: @@ -369,7 +369,7 @@ int tty_port_block_til_ready(struct tty_port *port, tty_port_set_active(port, 1); return 0; } - if (filp->f_flags & O_NONBLOCK) { + if (filp == NULL || (filp->f_flags & O_NONBLOCK)) { /* Indicate we are open */ if (C_BAUD(tty)) tty_port_raise_dtr_rts(port); -- 2.20.1