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33f0f88f1c
The API and code have been through various bits of initial review by
serial driver people but they definitely need to live somewhere for a
while so the unconverted drivers can get knocked into shape, existing
drivers that have been updated can be better tuned and bugs whacked out.
This replaces the tty flip buffers with kmalloc objects in rings. In the
normal situation for an IRQ driven serial port at typical speeds the
behaviour is pretty much the same, two buffers end up allocated and the
kernel cycles between them as before.
When there are delays or at high speed we now behave far better as the
buffer pool can grow a bit rather than lose characters. This also means
that we can operate at higher speeds reliably.
For drivers that receive characters in blocks (DMA based, USB and
especially virtualisation) the layer allows a lot of driver specific
code that works around the tty layer with private secondary queues to be
removed. The IBM folks need this sort of layer, the smart serial port
people do, the virtualisers do (because a virtualised tty typically
operates at infinite speed rather than emulating 9600 baud).
Finally many drivers had invalid and unsafe attempts to avoid buffer
overflows by directly invoking tty methods extracted out of the innards
of work queue structs. These are no longer needed and all go away. That
fixes various random hangs with serial ports on overflow.
The other change in here is to optimise the receive_room path that is
used by some callers. It turns out that only one ldisc uses receive room
except asa constant and it updates it far far less than the value is
read. We thus make it a variable not a function call.
I expect the code to contain bugs due to the size alone but I'll be
watching and squashing them and feeding out new patches as it goes.
Because the buffers now dynamically expand you should only run out of
buffering when the kernel runs out of memory for real. That means a lot of
the horrible hacks high performance drivers used to do just aren't needed any
more.
Description:
tty_insert_flip_char is an old API and continues to work as before, as does
tty_flip_buffer_push() [this is why many drivers dont need modification]. It
does now also return the number of chars inserted
There are also
tty_buffer_request_room(tty, len)
which asks for a buffer block of the length requested and returns the space
found. This improves efficiency with hardware that knows how much to
transfer.
and tty_insert_flip_string_flags(tty, str, flags, len)
to insert a string of characters and flags
For a smart interface the usual code is
len = tty_request_buffer_room(tty, amount_hardware_says);
tty_insert_flip_string(tty, buffer_from_card, len);
More description!
At the moment tty buffers are attached directly to the tty. This is causing a
lot of the problems related to tty layer locking, also problems at high speed
and also with bursty data (such as occurs in virtualised environments)
I'm working on ripping out the flip buffers and replacing them with a pool of
dynamically allocated buffers. This allows both for old style "byte I/O"
devices and also helps virtualisation and smart devices where large blocks of
data suddenely materialise and need storing.
So far so good. Lots of drivers reference tty->flip.*. Several of them also
call directly and unsafely into function pointers it provides. This will all
break. Most drivers can use tty_insert_flip_char which can be kept as an API
but others need more.
At the moment I've added the following interfaces, if people think more will
be needed now is a good time to say
int tty_buffer_request_room(tty, size)
Try and ensure at least size bytes are available, returns actual room (may be
zero). At the moment it just uses the flipbuf space but that will change.
Repeated calls without characters being added are not cumulative. (ie if you
call it with 1, 1, 1, and then 4 you'll have four characters of space. The
other functions will also try and grow buffers in future but this will be a
more efficient way when you know block sizes.
int tty_insert_flip_char(tty, ch, flag)
As before insert a character if there is room. Now returns 1 for success, 0
for failure.
int tty_insert_flip_string(tty, str, len)
Insert a block of non error characters. Returns the number inserted.
int tty_prepare_flip_string(tty, strptr, len)
Adjust the buffer to allow len characters to be added. Returns a buffer
pointer in strptr and the length available. This allows for hardware that
needs to use functions like insl or mencpy_fromio.
Signed-off-by: Alan Cox <alan@redhat.com>
Cc: Paul Fulghum <paulkf@microgate.com>
Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>
Signed-off-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: John Hawkes <hawkes@sgi.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
146 lines
5.2 KiB
C
146 lines
5.2 KiB
C
#ifndef _LINUX_TTY_LDISC_H
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#define _LINUX_TTY_LDISC_H
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/*
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* This structure defines the interface between the tty line discipline
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* implementation and the tty routines. The following routines can be
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* defined; unless noted otherwise, they are optional, and can be
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* filled in with a null pointer.
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*
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* int (*open)(struct tty_struct *);
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*
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* This function is called when the line discipline is associated
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* with the tty. The line discipline can use this as an
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* opportunity to initialize any state needed by the ldisc routines.
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*
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* void (*close)(struct tty_struct *);
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*
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* This function is called when the line discipline is being
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* shutdown, either because the tty is being closed or because
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* the tty is being changed to use a new line discipline
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*
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* void (*flush_buffer)(struct tty_struct *tty);
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*
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* This function instructs the line discipline to clear its
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* buffers of any input characters it may have queued to be
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* delivered to the user mode process.
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*
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* ssize_t (*chars_in_buffer)(struct tty_struct *tty);
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*
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* This function returns the number of input characters the line
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* discipline may have queued up to be delivered to the user mode
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* process.
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*
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* ssize_t (*read)(struct tty_struct * tty, struct file * file,
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* unsigned char * buf, size_t nr);
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*
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* This function is called when the user requests to read from
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* the tty. The line discipline will return whatever characters
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* it has buffered up for the user. If this function is not
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* defined, the user will receive an EIO error.
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*
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* ssize_t (*write)(struct tty_struct * tty, struct file * file,
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* const unsigned char * buf, size_t nr);
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*
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* This function is called when the user requests to write to the
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* tty. The line discipline will deliver the characters to the
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* low-level tty device for transmission, optionally performing
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* some processing on the characters first. If this function is
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* not defined, the user will receive an EIO error.
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*
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* int (*ioctl)(struct tty_struct * tty, struct file * file,
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* unsigned int cmd, unsigned long arg);
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*
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* This function is called when the user requests an ioctl which
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* is not handled by the tty layer or the low-level tty driver.
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* It is intended for ioctls which affect line discpline
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* operation. Note that the search order for ioctls is (1) tty
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* layer, (2) tty low-level driver, (3) line discpline. So a
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* low-level driver can "grab" an ioctl request before the line
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* discpline has a chance to see it.
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*
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* void (*set_termios)(struct tty_struct *tty, struct termios * old);
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*
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* This function notifies the line discpline that a change has
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* been made to the termios structure.
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*
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* int (*poll)(struct tty_struct * tty, struct file * file,
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* poll_table *wait);
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*
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* This function is called when a user attempts to select/poll on a
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* tty device. It is solely the responsibility of the line
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* discipline to handle poll requests.
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*
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* void (*receive_buf)(struct tty_struct *, const unsigned char *cp,
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* char *fp, int count);
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*
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* This function is called by the low-level tty driver to send
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* characters received by the hardware to the line discpline for
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* processing. <cp> is a pointer to the buffer of input
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* character received by the device. <fp> is a pointer to a
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* pointer of flag bytes which indicate whether a character was
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* received with a parity error, etc.
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*
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* void (*write_wakeup)(struct tty_struct *);
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*
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* This function is called by the low-level tty driver to signal
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* that line discpline should try to send more characters to the
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* low-level driver for transmission. If the line discpline does
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* not have any more data to send, it can just return.
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*
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* int (*hangup)(struct tty_struct *)
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*
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* Called on a hangup. Tells the discipline that it should
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* cease I/O to the tty driver. Can sleep. The driver should
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* seek to perform this action quickly but should wait until
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* any pending driver I/O is completed.
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*/
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#include <linux/fs.h>
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#include <linux/wait.h>
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struct tty_ldisc {
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int magic;
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char *name;
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int num;
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int flags;
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/*
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* The following routines are called from above.
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*/
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int (*open)(struct tty_struct *);
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void (*close)(struct tty_struct *);
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void (*flush_buffer)(struct tty_struct *tty);
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ssize_t (*chars_in_buffer)(struct tty_struct *tty);
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ssize_t (*read)(struct tty_struct * tty, struct file * file,
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unsigned char __user * buf, size_t nr);
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ssize_t (*write)(struct tty_struct * tty, struct file * file,
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const unsigned char * buf, size_t nr);
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int (*ioctl)(struct tty_struct * tty, struct file * file,
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unsigned int cmd, unsigned long arg);
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void (*set_termios)(struct tty_struct *tty, struct termios * old);
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unsigned int (*poll)(struct tty_struct *, struct file *,
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struct poll_table_struct *);
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int (*hangup)(struct tty_struct *tty);
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/*
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* The following routines are called from below.
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*/
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void (*receive_buf)(struct tty_struct *, const unsigned char *cp,
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char *fp, int count);
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void (*write_wakeup)(struct tty_struct *);
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struct module *owner;
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int refcount;
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};
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#define TTY_LDISC_MAGIC 0x5403
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#define LDISC_FLAG_DEFINED 0x00000001
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#define MODULE_ALIAS_LDISC(ldisc) \
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MODULE_ALIAS("tty-ldisc-" __stringify(ldisc))
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#endif /* _LINUX_TTY_LDISC_H */
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