tty_outq.c

Go to the documentation of this file.

/*-
 * Copyright (c) 2008 Ed Schouten <ed@FreeBSD.org>
 * All rights reserved.
 *
 * Portions of this software were developed under sponsorship from Snow
 * B.V., the Netherlands.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__FBSDID("$BSDSUniX$");

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/queue.h>
#include <sys/systm.h>
#include <sys/tty.h>
#include <sys/uio.h>

#include <vm/uma.h>

/*
 * TTY output queue buffering.
 *
 * The previous design of the TTY layer offered the so-called clists.
 * These clists were used for both the input queues and the output
 * queue. We don't use certain features on the output side, like quoting
 * bits for parity marking and such. This mechanism is similar to the
 * old clists, but only contains the features we need to buffer the
 * output.
 */

struct ttyoutq_block {
        struct ttyoutq_block    *tob_next;
        char                    tob_data[TTYOUTQ_DATASIZE];
};

static uma_zone_t ttyoutq_zone;

#define TTYOUTQ_INSERT_TAIL(to, tob) do {                               \
        if (to->to_end == 0) {                                          \
                tob->tob_next = to->to_firstblock;                      \
                to->to_firstblock = tob;                                \
        } else {                                                        \
                tob->tob_next = to->to_lastblock->tob_next;             \
                to->to_lastblock->tob_next = tob;                       \
        }                                                               \
        to->to_nblocks++;                                               \
} while (0)

#define TTYOUTQ_REMOVE_HEAD(to) do {                                    \
        to->to_firstblock = to->to_firstblock->tob_next;                \
        to->to_nblocks--;                                               \
} while (0)

#define TTYOUTQ_RECYCLE(to, tob) do {                                   \
        if (to->to_quota <= to->to_nblocks)                             \
                uma_zfree(ttyoutq_zone, tob);                           \
        else                                                            \
                TTYOUTQ_INSERT_TAIL(to, tob);                           \
} while(0)

void
ttyoutq_flush(struct ttyoutq *to)
{

        to->to_begin = 0;
        to->to_end = 0;
}

void
ttyoutq_setsize(struct ttyoutq *to, struct tty *tp, size_t size)
{
        struct ttyoutq_block *tob;

        to->to_quota = howmany(size, TTYOUTQ_DATASIZE);

        while (to->to_quota > to->to_nblocks) {
                /*
                 * List is getting bigger.
                 * Add new blocks to the tail of the list.
                 *
                 * We must unlock the TTY temporarily, because we need
                 * to allocate memory. This won't be a problem, because
                 * in the worst case, another thread ends up here, which
                 * may cause us to allocate too many blocks, but this
                 * will be caught by the loop below.
                 */
                tty_unlock(tp);
                tob = uma_zalloc(ttyoutq_zone, M_WAITOK);
                tty_lock(tp);

                TTYOUTQ_INSERT_TAIL(to, tob);
        }
}

void
ttyoutq_free(struct ttyoutq *to)
{
        struct ttyoutq_block *tob;

        ttyoutq_flush(to);
        to->to_quota = 0;

        while ((tob = to->to_firstblock) != NULL) {
                TTYOUTQ_REMOVE_HEAD(to);
                uma_zfree(ttyoutq_zone, tob);
        }

        MPASS(to->to_nblocks == 0);
}

size_t
ttyoutq_read(struct ttyoutq *to, void *buf, size_t len)
{
        char *cbuf = buf;

        while (len > 0) {
                struct ttyoutq_block *tob;
                size_t cbegin, cend, clen;

                /* See if there still is data. */
                if (to->to_begin == to->to_end)
                        break;
                tob = to->to_firstblock;
                if (tob == NULL)
                        break;

                /*
                 * The end address should be the lowest of these three:
                 * - The write pointer
                 * - The blocksize - we can't read beyond the block
                 * - The end address if we could perform the full read
                 */
                cbegin = to->to_begin;
                cend = MIN(MIN(to->to_end, to->to_begin + len),
                    TTYOUTQ_DATASIZE);
                clen = cend - cbegin;

                /* Copy the data out of the buffers. */
                memcpy(cbuf, tob->tob_data + cbegin, clen);
                cbuf += clen;
                len -= clen;

                if (cend == to->to_end) {
                        /* Read the complete queue. */
                        to->to_begin = 0;
                        to->to_end = 0;
                } else if (cend == TTYOUTQ_DATASIZE) {
                        /* Read the block until the end. */
                        TTYOUTQ_REMOVE_HEAD(to);
                        to->to_begin = 0;
                        to->to_end -= TTYOUTQ_DATASIZE;
                        TTYOUTQ_RECYCLE(to, tob);
                } else {
                        /* Read the block partially. */
                        to->to_begin += clen;
                }
        }

        return (cbuf - (char *)buf);
}

/*
 * An optimized version of ttyoutq_read() which can be used in pseudo
 * TTY drivers to directly copy data from the outq to userspace, instead
 * of buffering it.
 *
 * We can only copy data directly if we need to read the entire block
 * back to the user, because we temporarily remove the block from the
 * queue. Otherwise we need to copy it to a temporary buffer first, to
 * make sure data remains in the correct order.
 */
int
ttyoutq_read_uio(struct ttyoutq *to, struct tty *tp, struct uio *uio)
{

        while (uio->uio_resid > 0) {
                int error;
                struct ttyoutq_block *tob;
                size_t cbegin, cend, clen;

                /* See if there still is data. */
                if (to->to_begin == to->to_end)
                        return (0);
                tob = to->to_firstblock;
                if (tob == NULL)
                        return (0);

                /*
                 * The end address should be the lowest of these three:
                 * - The write pointer
                 * - The blocksize - we can't read beyond the block
                 * - The end address if we could perform the full read
                 */
                cbegin = to->to_begin;
                cend = MIN(MIN(to->to_end, to->to_begin + uio->uio_resid),
                    TTYOUTQ_DATASIZE);
                clen = cend - cbegin;

                /*
                 * We can prevent buffering in some cases:
                 * - We need to read the block until the end.
                 * - We don't need to read the block until the end, but
                 *   there is no data beyond it, which allows us to move
                 *   the write pointer to a new block.
                 */
                if (cend == TTYOUTQ_DATASIZE || cend == to->to_end) {
                        /*
                         * Fast path: zero copy. Remove the first block,
                         * so we can unlock the TTY temporarily.
                         */
                        TTYOUTQ_REMOVE_HEAD(to);
                        to->to_begin = 0;
                        if (to->to_end <= TTYOUTQ_DATASIZE)
                                to->to_end = 0;
                        else
                                to->to_end -= TTYOUTQ_DATASIZE;

                        /* Temporary unlock and copy the data to userspace. */
                        tty_unlock(tp);
                        error = uiomove(tob->tob_data + cbegin, clen, uio);
                        tty_lock(tp);

                        /* Block can now be readded to the list. */
                        TTYOUTQ_RECYCLE(to, tob);
                } else {
                        char ob[TTYOUTQ_DATASIZE - 1];

                        /*
                         * Slow path: store data in a temporary buffer.
                         */
                        memcpy(ob, tob->tob_data + cbegin, clen);
                        to->to_begin += clen;
                        MPASS(to->to_begin < TTYOUTQ_DATASIZE);

                        /* Temporary unlock and copy the data to userspace. */
                        tty_unlock(tp);
                        error = uiomove(ob, clen, uio);
                        tty_lock(tp);
                }

                if (error != 0)
                        return (error);
        }

        return (0);
}

size_t
ttyoutq_write(struct ttyoutq *to, const void *buf, size_t nbytes)
{
        const char *cbuf = buf;
        struct ttyoutq_block *tob;
        unsigned int boff;
        size_t l;

        while (nbytes > 0) {
                boff = to->to_end % TTYOUTQ_DATASIZE;

                if (to->to_end == 0) {
                        /* First time we're being used or drained. */
                        MPASS(to->to_begin == 0);
                        tob = to->to_firstblock;
                        if (tob == NULL) {
                                /* Queue has no blocks. */
                                break;
                        }
                        to->to_lastblock = tob;
                } else if (boff == 0) {
                        /* We reached the end of this block on last write. */
                        tob = to->to_lastblock->tob_next;
                        if (tob == NULL) {
                                /* We've reached the watermark. */
                                break;
                        }
                        to->to_lastblock = tob;
                } else {
                        tob = to->to_lastblock;
                }

                /* Don't copy more than was requested. */
                l = MIN(nbytes, TTYOUTQ_DATASIZE - boff);
                MPASS(l > 0);
                memcpy(tob->tob_data + boff, cbuf, l);

                cbuf += l;
                nbytes -= l;
                to->to_end += l;
        }

        return (cbuf - (const char *)buf);
}

int
ttyoutq_write_nofrag(struct ttyoutq *to, const void *buf, size_t nbytes)
{
        size_t ret;

        if (ttyoutq_bytesleft(to) < nbytes)
                return (-1);

        /* We should always be able to write it back. */
        ret = ttyoutq_write(to, buf, nbytes);
        MPASS(ret == nbytes);

        return (0);
}

static void
ttyoutq_startup(void *dummy)
{

        ttyoutq_zone = uma_zcreate("ttyoutq", sizeof(struct ttyoutq_block),
            NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
}

SYSINIT(ttyoutq, SI_SUB_DRIVERS, SI_ORDER_FIRST, ttyoutq_startup, NULL);