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* [patch 0/7] staging: speakup: introduce tty-based comms
@  okash.khawaja
   ` [patch 1/7] tty_port: allow a port to be opened with a tty that has no file handle okash.khawaja
                   ` (8 more replies)
  0 siblings, 9 replies; 21+ messages in thread
From: okash.khawaja @  UTC (permalink / raw)
  To: Greg Kroah-Hartman, Jiri Slaby, Samuel Thibault, linux-kernel
  Cc: William Hubbs, Chris Brannon, Kirk Reiser, speakup, devel

Hi,

This patchset introduces a TTY-based way for the synths to communicate
with devices as an alternate for direct serial comms used by the synths
at the moment. It then migrates some of the synths to the TTY-based
comms. Synths migrated in this patchset are dummy, acntsa, bns and
txprt.

As such, this series is meant to start a discussion on the changes in the
first patch: "tty_port: allow a port to be opened with a tty that has no
file handle". This allows speakup to access tty port early on during boot,
making it possible to start emiting messages as early as possible. This is
demonstrated in patch 6, where it calls tty_open_by_driver, passing in NULL
for inode and filp params.

To wrap up, here is a summary of the patches that follow. Patch 1 enables
kernel access to TTY device. Patches 2 - 5 prepare the code to accomodate
TTY-based comms as an alternate to raw serial I/O for outputting data to
external device. Patch 6 builds upon the changes made in patch 1 and utilises
TTY-subsystem to communicate with external device - currently just over ttyS*
but with plans to expand it to other TTY devices soon. Finally, patch 7 does
actual migration of some of the simple synths from raw serial comms to TTY.

Okash

^ permalink raw reply	[flat|nested] 21+ messages in thread
* [patch 1/7] tty_port: allow a port to be opened with a tty that has no file handle
@  okash.khawaja
   ` Samuel Thibault
  0 siblings, 1 reply; 21+ messages in thread
From: okash.khawaja @  UTC (permalink / raw)
  To: samuel.thibault; +Cc: speakup, Okash Khawaja

[-- Attachment #1: 01_enable_kernel_access_to_tty_device --]
[-- Type: text/plain, Size: 4257 bytes --]

Allow access to TTY device from kernel. This is based on Alan Cox's patch
(http://www.mail-archive.com/linux-kernel at vger.kernel.org/msg1215095.html),
with description quoted below.

"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.

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: Okash Khawaja <okash.khawaja@gmail.com>

Index: linux-4.10.1/drivers/tty/tty_io.c
===================================================================
--- linux-4.10.1.orig/drivers/tty/tty_io.c
+++ linux-4.10.1/drivers/tty/tty_io.c
@@ -855,7 +855,7 @@
 
 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);
@@ -1368,7 +1368,10 @@
 	struct tty_struct *tty;
 
 	if (driver->ops->lookup)
-		tty = driver->ops->lookup(driver, file, idx);
+		if (!file)
+			tty = ERR_PTR(-EIO);
+		else
+			tty = driver->ops->lookup(driver, file, idx);
 	else
 		tty = driver->ttys[idx];
 
@@ -1986,7 +1989,7 @@
 		struct tty_driver *console_driver = console_device(index);
 		if (console_driver) {
 			driver = tty_driver_kref_get(console_driver);
-			if (driver) {
+			if (driver && filp) {
 				/* Don't let /dev/console block */
 				filp->f_flags |= O_NONBLOCK;
 				break;
@@ -2019,7 +2022,7 @@
  *	  - concurrent tty driver removal w/ lookup
  *	  - concurrent tty removal from driver table
  */
-static struct tty_struct *tty_open_by_driver(dev_t device, struct inode *inode,
+struct tty_struct *tty_open_by_driver(dev_t device, struct inode *inode,
 					     struct file *filp)
 {
 	struct tty_struct *tty;
@@ -2064,6 +2067,7 @@
 	tty_driver_kref_put(driver);
 	return tty;
 }
+EXPORT_SYMBOL(tty_open_by_driver);
 
 /**
  *	tty_open		-	open a tty device
Index: linux-4.10.1/drivers/tty/tty_port.c
===================================================================
--- linux-4.10.1.orig/drivers/tty/tty_port.c
+++ linux-4.10.1/drivers/tty/tty_port.c
@@ -335,7 +335,7 @@
  *	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 @@
 		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);
Index: linux-4.10.1/include/linux/tty.h
===================================================================
--- linux-4.10.1.orig/include/linux/tty.h
+++ linux-4.10.1/include/linux/tty.h
@@ -394,6 +394,8 @@
 /* tty_io.c */
 extern int __init tty_init(void);
 extern const char *tty_name(const struct tty_struct *tty);
+extern struct tty_struct *tty_open_by_driver(dev_t device, struct inode *inode,
+					     struct file *filp);
 #else
 static inline void console_init(void)
 { }


^ permalink raw reply	[flat|nested] 21+ messages in thread
end of thread, other threads:[~ UTC | newest]

Thread overview: 21+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
 [patch 0/7] staging: speakup: introduce tty-based comms okash.khawaja
 ` [patch 1/7] tty_port: allow a port to be opened with a tty that has no file handle okash.khawaja
     [not found]   ` <20170313221247.GA22823@kroah.com>
     ` Okash Khawaja
 ` [patch 2/7] staging: speakup: spk_serial_out and spk_wait_for_xmitr to take synth arg okash.khawaja
 ` [patch 3/7] staging: serial: add spk_io_ops struct to spk_synth okash.khawaja
 ` [patch 4/7] staging: speakup: move spk_stop_serial_interrupt into synth-specific release function okash.khawaja
 ` [patch 5/7] staging: speakup: move those functions which do outgoing serial comms, into serialio.c okash.khawaja
 ` [patch 6/7] staging: speakup: add tty-based comms functions okash.khawaja
 ` [patch 7/7] staging: speakup: migrate acntsa, bns, dummy and txprt to ttyio okash.khawaja
 ` [patch 0/7] staging: speakup: introduce tty-based comms Samuel Thibault
     [not found] ` <20170313221404.GA22871@kroah.com>
   ` Samuel Thibault
     [not found]     ` <20170313234303.GA14626@kroah.com>
       ` Samuel Thibault
     ` Samuel Thibault
   ` Samuel Thibault
     ` Samuel Thibault
     [not found]       ` <CAL_JsqJVfG2pFoNtj89e0E9OKye4wGEUi98NOnMBwNF+Yp-rPA@mail.gmail.com>
         ` Samuel Thibault
           ` Samuel Thibault
             ` Okash Khawaja
     ` Samuel Thibault
  -- strict thread matches above, loose matches on Subject: below --
 [patch 1/7] tty_port: allow a port to be opened with a tty that has no file handle okash.khawaja
 ` Samuel Thibault

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