rt-thread/components/lwp/terminal/freebsd/tty_outq.c

/*
 * Copyright (c) 2006-2023, RT-Thread Development Team
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Change Logs:
 * Date           Author       Notes
 * 2023-11-13     Shell        init ver.
 */

#include "../bsd_porting.h"
#include "../terminal.h"

/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * 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.
 */

/*
 * 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;
}

int ttyoutq_setsize(struct ttyoutq *to, struct lwp_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);

        if (tty_gone(tp))
        {
            uma_zfree(ttyoutq_zone, tob);
            return -ENXIO;
        }

        TTYOUTQ_INSERT_TAIL(to, tob);
    }
    return 0;
}

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 lwp_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 __unused;

    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 int ttyoutq_startup(void)
{
    ttyoutq_zone = uma_zcreate("ttyoutq", sizeof(struct ttyoutq_block), NULL,
                               NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
    return 0;
}
INIT_PREV_EXPORT(ttyoutq_startup);

#if 0
SYSINIT(ttyoutq, SI_SUB_DRIVERS, SI_ORDER_FIRST, ttyoutq_startup, NULL);
#endif