diff options
Diffstat (limited to 'sys/kern/tty_outq.c')
| -rw-r--r-- | sys/kern/tty_outq.c | 365 |
1 files changed, 365 insertions, 0 deletions
diff --git a/sys/kern/tty_outq.c b/sys/kern/tty_outq.c new file mode 100644 index 000000000000..e945ccab0b48 --- /dev/null +++ b/sys/kern/tty_outq.c @@ -0,0 +1,365 @@ +/*- + * 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("$FreeBSD$"); + +#include <sys/param.h> +#include <sys/kernel.h> +#include <sys/lock.h> +#include <sys/queue.h> +#include <sys/sysctl.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. + */ + +/* Statistics. */ +static long ttyoutq_nfast = 0; +SYSCTL_LONG(_kern, OID_AUTO, tty_outq_nfast, CTLFLAG_RD, + &ttyoutq_nfast, 0, "Unbuffered reads to userspace on output"); +static long ttyoutq_nslow = 0; +SYSCTL_LONG(_kern, OID_AUTO, tty_outq_nslow, CTLFLAG_RD, + &ttyoutq_nslow, 0, "Buffered reads to userspace on output"); + +struct ttyoutq_block { + STAILQ_ENTRY(ttyoutq_block) tob_list; + char tob_data[TTYOUTQ_DATASIZE]; +}; + +static uma_zone_t ttyoutq_zone; + +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) +{ + unsigned int nblocks; + struct ttyoutq_block *tob; + + nblocks = howmany(size, TTYOUTQ_DATASIZE); + + while (nblocks > 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)) + return; + + STAILQ_INSERT_TAIL(&to->to_list, tob, tob_list); + to->to_nblocks++; + } + + while (nblocks < to->to_nblocks) { + /* + * List is getting smaller. Remove unused blocks at the + * end. This means we cannot guarantee this routine + * shrinks buffers properly, when we need to reclaim + * more space than there is available. + * + * XXX TODO: Two solutions here: + * - Throw data away + * - Temporarily hit the watermark until enough data has + * been flushed, so we can remove the blocks. + */ + + if (to->to_end == 0) { + tob = STAILQ_FIRST(&to->to_list); + if (tob == NULL) + break; + STAILQ_REMOVE_HEAD(&to->to_list, tob_list); + } else { + tob = STAILQ_NEXT(to->to_lastblock, tob_list); + if (tob == NULL) + break; + STAILQ_REMOVE_NEXT(&to->to_list, to->to_lastblock, tob_list); + } + uma_zfree(ttyoutq_zone, tob); + to->to_nblocks--; + } +} + +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 = STAILQ_FIRST(&to->to_list); + 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; + + if (cend == TTYOUTQ_DATASIZE || cend == to->to_end) { + /* Read the block until the end. */ + STAILQ_REMOVE_HEAD(&to->to_list, tob_list); + STAILQ_INSERT_TAIL(&to->to_list, tob, tob_list); + to->to_begin = 0; + if (to->to_end <= TTYOUTQ_DATASIZE) { + to->to_end = 0; + } else { + to->to_end -= TTYOUTQ_DATASIZE; + } + } else { + /* Read the block partially. */ + to->to_begin += clen; + } + + /* Copy the data out of the buffers. */ + memcpy(cbuf, tob->tob_data + cbegin, clen); + cbuf += clen; + len -= 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 = STAILQ_FIRST(&to->to_list); + 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) { + atomic_add_long(&ttyoutq_nfast, 1); + + /* + * Fast path: zero copy. Remove the first block, + * so we can unlock the TTY temporarily. + */ + STAILQ_REMOVE_HEAD(&to->to_list, tob_list); + to->to_nblocks--; + 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); + + if (tty_gone(tp)) { + /* We lost the discipline. */ + uma_zfree(ttyoutq_zone, tob); + return (ENXIO); + } + + /* Block can now be readded to the list. */ + /* + * XXX: we could remove the blocks here when the + * queue was shrunk, but still in use. See + * ttyoutq_setsize(). + */ + STAILQ_INSERT_TAIL(&to->to_list, tob, tob_list); + to->to_nblocks++; + if (error != 0) + return (error); + } else { + char ob[TTYOUTQ_DATASIZE - 1]; + atomic_add_long(&ttyoutq_nslow, 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 (tty_gone(tp)) { + /* We lost the discipline. */ + return (ENXIO); + } + + 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) { + /* Offset in current block. */ + tob = to->to_lastblock; + 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_lastblock = STAILQ_FIRST(&to->to_list); + if (tob == NULL) { + /* Queue has no blocks. */ + break; + } + } else if (boff == 0) { + /* We reached the end of this block on last write. */ + tob = STAILQ_NEXT(tob, tob_list); + if (tob == NULL) { + /* We've reached the watermark. */ + break; + } + to->to_lastblock = tob; + } + + /* 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); |