diff options
Diffstat (limited to 'drivers/char/pty.c')
| -rw-r--r-- | drivers/char/pty.c | 155 |
1 files changed, 61 insertions, 94 deletions
diff --git a/drivers/char/pty.c b/drivers/char/pty.c index daebe1ba43d4..d083c73d784a 100644 --- a/drivers/char/pty.c +++ b/drivers/char/pty.c @@ -22,6 +22,7 @@ #include <linux/major.h> #include <linux/mm.h> #include <linux/init.h> +#include <linux/smp_lock.h> #include <linux/sysctl.h> #include <linux/device.h> #include <linux/uaccess.h> @@ -75,114 +76,90 @@ static void pty_close(struct tty_struct *tty, struct file *filp) */ static void pty_unthrottle(struct tty_struct *tty) { - struct tty_struct *o_tty = tty->link; - - if (!o_tty) - return; - - tty_wakeup(o_tty); + tty_wakeup(tty->link); set_bit(TTY_THROTTLED, &tty->flags); } -/* - * WSH 05/24/97: modified to - * (1) use space in tty->flip instead of a shared temp buffer - * The flip buffers aren't being used for a pty, so there's lots - * of space available. The buffer is protected by a per-pty - * semaphore that should almost never come under contention. - * (2) avoid redundant copying for cases where count >> receive_room - * N.B. Calls from user space may now return an error code instead of - * a count. +/** + * pty_space - report space left for writing + * @to: tty we are writing into * - * FIXME: Our pty_write method is called with our ldisc lock held but - * not our partners. We can't just wait on the other one blindly without - * risking deadlocks. At some point when everything has settled down we need - * to look into making pty_write at least able to sleep over an ldisc change. + * The tty buffers allow 64K but we sneak a peak and clip at 8K this + * allows a lot of overspill room for echo and other fun messes to + * be handled properly + */ + +static int pty_space(struct tty_struct *to) +{ + int n = 8192 - to->buf.memory_used; + if (n < 0) + return 0; + return n; +} + +/** + * pty_write - write to a pty + * @tty: the tty we write from + * @buf: kernel buffer of data + * @count: bytes to write * - * The return on no ldisc is a bit counter intuitive but the logic works - * like this. During an ldisc change the other end will flush its buffers. We - * thus return the full length which is identical to the case where we had - * proper locking and happened to queue the bytes just before the flush during - * the ldisc change. + * Our "hardware" write method. Data is coming from the ldisc which + * may be in a non sleeping state. We simply throw this at the other + * end of the link as if we were an IRQ handler receiving stuff for + * the other side of the pty/tty pair. */ + static int pty_write(struct tty_struct *tty, const unsigned char *buf, int count) { struct tty_struct *to = tty->link; - struct tty_ldisc *ld; - int c = count; + int c; - if (!to || tty->stopped) + if (tty->stopped) return 0; - ld = tty_ldisc_ref(to); - - if (ld) { - c = to->receive_room; - if (c > count) - c = count; - ld->ops->receive_buf(to, buf, NULL, c); - tty_ldisc_deref(ld); + + /* This isn't locked but our 8K is quite sloppy so no + big deal */ + + c = pty_space(to); + if (c > count) + c = count; + if (c > 0) { + /* Stuff the data into the input queue of the other end */ + c = tty_insert_flip_string(to, buf, c); + /* And shovel */ + tty_flip_buffer_push(to); + tty_wakeup(tty); } return c; } +/** + * pty_write_room - write space + * @tty: tty we are writing from + * + * Report how many bytes the ldisc can send into the queue for + * the other device. + */ + static int pty_write_room(struct tty_struct *tty) { - struct tty_struct *to = tty->link; - - if (!to || tty->stopped) + if (tty->stopped) return 0; - - return to->receive_room; + return pty_space(tty->link); } -/* - * WSH 05/24/97: Modified for asymmetric MASTER/SLAVE behavior - * The chars_in_buffer() value is used by the ldisc select() function - * to hold off writing when chars_in_buffer > WAKEUP_CHARS (== 256). - * The pty driver chars_in_buffer() Master/Slave must behave differently: - * - * The Master side needs to allow typed-ahead commands to accumulate - * while being canonicalized, so we report "our buffer" as empty until - * some threshold is reached, and then report the count. (Any count > - * WAKEUP_CHARS is regarded by select() as "full".) To avoid deadlock - * the count returned must be 0 if no canonical data is available to be - * read. (The N_TTY ldisc.chars_in_buffer now knows this.) +/** + * pty_chars_in_buffer - characters currently in our tx queue + * @tty: our tty * - * The Slave side passes all characters in raw mode to the Master side's - * buffer where they can be read immediately, so in this case we can - * return the true count in the buffer. + * Report how much we have in the transmit queue. As everything is + * instantly at the other end this is easy to implement. */ + static int pty_chars_in_buffer(struct tty_struct *tty) { - struct tty_struct *to = tty->link; - struct tty_ldisc *ld; - int count = 0; - - /* We should get the line discipline lock for "tty->link" */ - if (!to) - return 0; - /* We cannot take a sleeping reference here without deadlocking with - an ldisc change - but it doesn't really matter */ - ld = tty_ldisc_ref(to); - if (ld == NULL) - return 0; - - /* The ldisc must report 0 if no characters available to be read */ - if (ld->ops->chars_in_buffer) - count = ld->ops->chars_in_buffer(to); - - tty_ldisc_deref(ld); - - if (tty->driver->subtype == PTY_TYPE_SLAVE) - return count; - - /* Master side driver ... if the other side's read buffer is less than - * half full, return 0 to allow writers to proceed; otherwise return - * the count. This leaves a comfortable margin to avoid overflow, - * and still allows half a buffer's worth of typed-ahead commands. - */ - return (count < N_TTY_BUF_SIZE/2) ? 0 : count; + return 0; } /* Set the lock flag on a pty */ @@ -202,20 +179,10 @@ static void pty_flush_buffer(struct tty_struct *tty) { struct tty_struct *to = tty->link; unsigned long flags; - struct tty_ldisc *ld; if (!to) return; - ld = tty_ldisc_ref(to); - - /* The other end is changing discipline */ - if (!ld) - return; - - if (ld->ops->flush_buffer) - to->ldisc->ops->flush_buffer(to); - tty_ldisc_deref(ld); - + /* tty_buffer_flush(to); FIXME */ if (to->packet) { spin_lock_irqsave(&tty->ctrl_lock, flags); tty->ctrl_status |= TIOCPKT_FLUSHWRITE; |