src/lib/ostream-file.c

	ostream-file.c revision bad44d7239e5d1163aadff48ea8ca96d01ed1561
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz/* Copyright (c) 2002-2007 Dovecot authors, see the included COPYING file */
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz/* @UNSAFE: whole file */
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz#include "lib.h"
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz#include "ioloop.h"
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz#include "write-full.h"
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz#include "network.h"
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz#include "sendfile-util.h"
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz#include "istream.h"
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz#include "istream-internal.h"
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz#include "ostream-internal.h"
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz#include <unistd.h>
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz#include <sys/stat.h>
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz#ifdef HAVE_SYS_UIO_H
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz#  include <sys/uio.h>
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz#endif
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz/* try to keep the buffer size within 4k..128k. ReiserFS may actually return
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz   128k as optimal size. */
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz#define DEFAULT_OPTIMAL_BLOCK_SIZE 4096
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz#define MAX_OPTIMAL_BLOCK_SIZE (128*1024)
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz#define IS_STREAM_EMPTY(fstream) \
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz    ((fstream)->head == (fstream)->tail && !(fstream)->full)
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz#define MAX_SSIZE_T(size) \
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz    ((size) < SSIZE_T_MAX ? (size_t)(size) : SSIZE_T_MAX)
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarzstruct file_ostream {
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz    struct ostream_private ostream;
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz
51ed197520dd9ea534fbc3bc1790ebe3cb5421e2Michael M Slusarz    int fd;
    struct io *io;
    uoff_t buffer_offset;
    uoff_t real_offset;

    unsigned char *buffer; /* ring-buffer */
    size_t buffer_size, max_buffer_size, optimal_block_size;
    size_t head, tail; /* first unsent/unused byte */

    unsigned int full:1; /* if head == tail, is buffer empty or full? */
    unsigned int file:1;
    unsigned int corked:1;
    unsigned int flush_pending:1;
    unsigned int socket_cork_set:1;
    unsigned int no_socket_cork:1;
    unsigned int no_sendfile:1;
    unsigned int autoclose_fd:1;
};

static void stream_send_io(struct file_ostream *fstream);

static void stream_closed(struct file_ostream *fstream)
{
    if (fstream->io != NULL)
        io_remove(&fstream->io);

    if (fstream->autoclose_fd && fstream->fd != -1) {
        if (close(fstream->fd) < 0)
            i_error("file_ostream.close() failed: %m");
    }
    fstream->fd = -1;

    fstream->ostream.ostream.closed = TRUE;
}

static void o_stream_file_close(struct iostream_private *stream)
{
    struct file_ostream *fstream = (struct file_ostream *)stream;

    /* flush output before really closing it */
    o_stream_flush(&fstream->ostream.ostream);

    stream_closed(fstream);
}

static void o_stream_file_destroy(struct iostream_private *stream)
{
    struct file_ostream *fstream = (struct file_ostream *)stream;

    i_free(fstream->buffer);
}

static void
o_stream_file_set_max_buffer_size(struct iostream_private *stream,
                  size_t max_size)
{
    struct file_ostream *fstream = (struct file_ostream *)stream;

    fstream->max_buffer_size = max_size;
}

static void update_buffer(struct file_ostream *fstream, size_t size)
{
    size_t used;

    if (IS_STREAM_EMPTY(fstream) || size == 0)
        return;

    if (fstream->head < fstream->tail) {
        /* ...HXXXT... */
        used = fstream->tail - fstream->head;
        i_assert(size <= used);
        fstream->head += size;
    } else {
        /* XXXT...HXXX */
        used = fstream->buffer_size - fstream->head;
        if (size > used) {
            size -= used;
            i_assert(size <= fstream->tail);
            fstream->head = size;
        } else {
            fstream->head += size;
        }

        fstream->full = FALSE;
    }

    if (fstream->head == fstream->tail)
        fstream->head = fstream->tail = 0;

    if (fstream->head == fstream->buffer_size)
        fstream->head = 0;
}

static void o_stream_socket_cork(struct file_ostream *fstream)
{
    if (fstream->corked && !fstream->socket_cork_set) {
        if (!fstream->no_socket_cork) {
            if (net_set_cork(fstream->fd, TRUE) < 0)
                fstream->no_socket_cork = TRUE;
            else
                fstream->socket_cork_set = TRUE;
        }
    }
}

static int o_stream_lseek(struct file_ostream *fstream)
{
    off_t ret;

    if (fstream->real_offset == fstream->buffer_offset)
        return 0;

    ret = lseek(fstream->fd, (off_t)fstream->buffer_offset, SEEK_SET);
    if (ret < 0) {
        fstream->ostream.ostream.stream_errno = errno;
        return -1;
    }

    if (ret != (off_t)fstream->buffer_offset) {
        fstream->ostream.ostream.stream_errno = EINVAL;
        return -1;
    }
    fstream->real_offset = fstream->buffer_offset;
    return 0;
}

static ssize_t o_stream_writev(struct file_ostream *fstream,
                   const struct const_iovec *iov, int iov_size)
{
    ssize_t ret;
    size_t size, sent;
    int i;

    o_stream_socket_cork(fstream);
    if (iov_size == 1) {
        if (!fstream->file ||
            fstream->real_offset == fstream->buffer_offset) {
            ret = write(fstream->fd, iov->iov_base, iov->iov_len);
            if (ret > 0)
                fstream->real_offset += ret;
        } else {
            ret = pwrite(fstream->fd, iov->iov_base, iov->iov_len,
                     fstream->buffer_offset);
        }
    } else {
        if (o_stream_lseek(fstream) < 0)
            return -1;

        sent = 0;
        while (iov_size > IOV_MAX) {
            size = 0;
            for (i = 0; i < IOV_MAX; i++)
                size += iov[i].iov_len;

            ret = writev(fstream->fd, (const struct iovec *)iov,
                     IOV_MAX);
            if (ret != (ssize_t)size)
                break;

            fstream->real_offset += ret;
            fstream->buffer_offset += ret;
            sent += ret;
            iov += IOV_MAX;
            iov_size -= IOV_MAX;
        }

        if (iov_size <= IOV_MAX) {
            ret = writev(fstream->fd, (const struct iovec *)iov,
                     iov_size);
        }
        if (ret > 0) {
            fstream->real_offset += ret;
            ret += sent;
        } else if (!fstream->file && sent > 0) {
            /* return what we managed to get sent */
            ret = sent;
        }
    }

    if (ret < 0) {
        if (errno == EAGAIN || errno == EINTR)
            return 0;
        fstream->ostream.ostream.stream_errno = errno;
        stream_closed(fstream);
        return -1;
    }
    if (unlikely(ret == 0 && fstream->file)) {
        /* assume out of disk space */
        fstream->ostream.ostream.stream_errno = ENOSPC;
        stream_closed(fstream);
        return -1;
    }

    fstream->buffer_offset += ret;
    return ret;
}

/* returns how much of vector was used */
static int o_stream_fill_iovec(struct file_ostream *fstream,
                   struct const_iovec iov[2])
{
    if (IS_STREAM_EMPTY(fstream))
        return 0;

    if (fstream->head < fstream->tail) {
        iov[0].iov_base = fstream->buffer + fstream->head;
        iov[0].iov_len = fstream->tail - fstream->head;
        return 1;
    } else {
        iov[0].iov_base = fstream->buffer + fstream->head;
        iov[0].iov_len = fstream->buffer_size - fstream->head;
        if (fstream->tail == 0)
            return 1;
        else {
            iov[1].iov_base = fstream->buffer;
            iov[1].iov_len = fstream->tail;
            return 2;
        }
    }
}

static int buffer_flush(struct file_ostream *fstream)
{
    struct const_iovec iov[2];
    int iov_len;
    ssize_t ret;

    iov_len = o_stream_fill_iovec(fstream, iov);
    if (iov_len > 0) {
        ret = o_stream_writev(fstream, iov, iov_len);
        if (ret < 0)
            return -1;

        update_buffer(fstream, ret);
    }

    return IS_STREAM_EMPTY(fstream) ? 1 : 0;
}

static void o_stream_file_cork(struct ostream_private *stream, bool set)
{
    struct file_ostream *fstream = (struct file_ostream *)stream;
    int ret;

    if (fstream->corked != set && !stream->ostream.closed) {
        if (set && fstream->io != NULL)
            io_remove(&fstream->io);
        else if (!set) {
            /* buffer flushing might close the stream */
            ret = buffer_flush(fstream);
            if (fstream->io == NULL &&
                (ret == 0 || fstream->flush_pending) &&
                !stream->ostream.closed) {
                fstream->io = io_add(fstream->fd, IO_WRITE,
                             stream_send_io, fstream);
            }
        }

        if (fstream->socket_cork_set) {
            i_assert(!set);
            if (net_set_cork(fstream->fd, FALSE) < 0)
                fstream->no_socket_cork = TRUE;
            fstream->socket_cork_set = FALSE;
        }
        fstream->corked = set;
    }
}

static int o_stream_file_flush(struct ostream_private *stream)
{
    struct file_ostream *fstream = (struct file_ostream *) stream;

    return buffer_flush(fstream);
}

static void
o_stream_file_flush_pending(struct ostream_private *stream, bool set)
{
    struct file_ostream *fstream = (struct file_ostream *) stream;

    fstream->flush_pending = set;
    if (set && !fstream->corked && fstream->io == NULL) {
        fstream->io = io_add(fstream->fd, IO_WRITE,
                     stream_send_io, fstream);
    }
}

static size_t get_unused_space(struct file_ostream *fstream)
{
    if (fstream->head > fstream->tail) {
        /* XXXT...HXXX */
        return fstream->head - fstream->tail;
    } else if (fstream->head < fstream->tail) {
        /* ...HXXXT... */
        return (fstream->buffer_size - fstream->tail) + fstream->head;
    } else {
        /* either fully unused or fully used */
        return fstream->full ? 0 : fstream->buffer_size;
    }
}

static size_t o_stream_file_get_used_size(struct ostream_private *stream)
{
    struct file_ostream *fstream = (struct file_ostream *)stream;

    return fstream->buffer_size - get_unused_space(fstream);
}

static int o_stream_file_seek(struct ostream_private *stream, uoff_t offset)
{
    struct file_ostream *fstream = (struct file_ostream *)stream;

    if (offset > OFF_T_MAX || !fstream->file) {
        stream->ostream.stream_errno = EINVAL;
        return -1;
    }

    if (buffer_flush(fstream) < 0)
        return -1;

    stream->ostream.offset = offset;
    fstream->buffer_offset = offset;
    return 1;
}

static void o_stream_grow_buffer(struct file_ostream *fstream, size_t bytes)
{
    size_t size, new_size, end_size;

    size = nearest_power(fstream->buffer_size + bytes);
    if (size > fstream->max_buffer_size) {
        /* limit the size */
        size = fstream->max_buffer_size;
    } else if (fstream->corked) {
        /* try to use optimal buffer size with corking */
        new_size = I_MIN(fstream->optimal_block_size,
                 fstream->max_buffer_size);
        if (new_size > size)
            size = new_size;
    }

    if (size <= fstream->buffer_size)
        return;

    fstream->buffer = i_realloc(fstream->buffer,
                    fstream->buffer_size, size);

    if (fstream->tail <= fstream->head && !IS_STREAM_EMPTY(fstream)) {
        /* move head forward to end of buffer */
        end_size = fstream->buffer_size - fstream->head;
        memmove(fstream->buffer + size - end_size,
            fstream->buffer + fstream->head, end_size);
        fstream->head = size - end_size;
    }

    fstream->full = FALSE;
    fstream->buffer_size = size;
}

static void stream_send_io(struct file_ostream *fstream)
{
    struct ostream *ostream = &fstream->ostream.ostream;
    int ret;

    /* Set flush_pending = FALSE first before calling the flush callback,
       and change it to TRUE only if callback returns 0. That way the
       callback can call o_stream_set_flush_pending() again and we don't
       forget it even if flush callback returns 1. */
    fstream->flush_pending = FALSE;

    o_stream_ref(ostream);
    if (fstream->ostream.callback != NULL)
        ret = fstream->ostream.callback(fstream->ostream.context);
    else
        ret = o_stream_file_flush(&fstream->ostream);

    if (ret == 0)
        fstream->flush_pending = TRUE;

    if (!fstream->flush_pending && IS_STREAM_EMPTY(fstream)) {
        if (fstream->io != NULL) {
            /* all sent */
            io_remove(&fstream->io);
        }
    } else if (!fstream->ostream.ostream.closed) {
        /* Add the IO handler if it's not there already. Callback
           might have just returned 0 without there being any data
           to be sent. */
        if (fstream->io == NULL) {
            fstream->io = io_add(fstream->fd, IO_WRITE,
                         stream_send_io, fstream);
        }
    }

    o_stream_unref(&ostream);
}

static size_t o_stream_add(struct file_ostream *fstream,
               const void *data, size_t size)
{
    size_t unused, sent;
    int i;

    unused = get_unused_space(fstream);
    if (unused < size)
        o_stream_grow_buffer(fstream, size-unused);

    sent = 0;
    for (i = 0; i < 2 && sent < size && !fstream->full; i++) {
        unused = fstream->tail >= fstream->head ?
            fstream->buffer_size - fstream->tail :
            fstream->head - fstream->tail;

        if (unused > size-sent)
            unused = size-sent;
        memcpy(fstream->buffer + fstream->tail,
               CONST_PTR_OFFSET(data, sent), unused);
        sent += unused;

        fstream->tail += unused;
        if (fstream->tail == fstream->buffer_size)
            fstream->tail = 0;

        if (fstream->head == fstream->tail)
            fstream->full = TRUE;
    }

    if (sent != 0 && fstream->io == NULL &&
        !fstream->corked && !fstream->file) {
        fstream->io = io_add(fstream->fd, IO_WRITE, stream_send_io,
                     fstream);
    }

    return sent;
}

static ssize_t o_stream_file_sendv(struct ostream_private *stream,
                   const struct const_iovec *iov,
                   unsigned int iov_count)
{
    struct file_ostream *fstream = (struct file_ostream *)stream;
    size_t size, total_size, added, optimal_size;
    unsigned int i;
    ssize_t ret = 0;

    for (i = 0, size = 0; i < iov_count; i++)
        size += iov[i].iov_len;
    total_size = size;

    if (size > get_unused_space(fstream) && !IS_STREAM_EMPTY(fstream)) {
        if (o_stream_file_flush(stream) < 0)
            return -1;
    }

    optimal_size = I_MIN(fstream->optimal_block_size,
                 fstream->max_buffer_size);
    if (IS_STREAM_EMPTY(fstream) &&
        (!fstream->corked || size >= optimal_size)) {
        /* send immediately */
        ret = o_stream_writev(fstream, iov, iov_count);
        if (ret < 0)
            return -1;

        size = ret;
        while (size > 0 && iov_count > 0 && size >= iov[0].iov_len) {
            size -= iov[0].iov_len;
            iov++;
            iov_count--;
        }

        if (iov_count == 0)
            i_assert(size == 0);
        else {
            added = o_stream_add(fstream,
                    CONST_PTR_OFFSET(iov[0].iov_base, size),
                    iov[0].iov_len - size);
            ret += added;

            if (added != iov[0].iov_len - size) {
                /* buffer full */
                stream->ostream.offset += ret;
                return ret;
            }

            iov++;
            iov_count--;
        }
    }

    /* buffer it, at least partly */
    for (i = 0; i < iov_count; i++) {
        added = o_stream_add(fstream, iov[i].iov_base, iov[i].iov_len);
        ret += added;
        if (added != iov[i].iov_len)
            break;
    }
    stream->ostream.offset += ret;
    i_assert((size_t)ret <= total_size);
    i_assert((size_t)ret == total_size || !fstream->file);
    return ret;
}

static off_t io_stream_sendfile(struct ostream_private *outstream,
                struct istream *instream, int in_fd)
{
    struct file_ostream *foutstream = (struct file_ostream *)outstream;
    const struct stat *st;
    uoff_t start_offset;
    uoff_t in_size, offset, send_size, v_offset;
    ssize_t ret;

    st = i_stream_stat(instream, TRUE);
    if (st == NULL) {
        outstream->ostream.stream_errno = instream->stream_errno;
        return -1;
    }
    in_size = st->st_size;

    o_stream_socket_cork(foutstream);

    /* flush out any data in buffer */
    if ((ret = buffer_flush(foutstream)) <= 0)
        return ret;

    if (o_stream_lseek(foutstream) < 0)
        return -1;

        start_offset = v_offset = instream->v_offset;
    do {
        offset = instream->real_stream->abs_start_offset + v_offset;
        send_size = in_size - v_offset;

        ret = safe_sendfile(foutstream->fd, in_fd, &offset,
                    MAX_SSIZE_T(send_size));
        if (ret <= 0) {
            if (ret == 0 || errno == EINTR || errno == EAGAIN) {
                ret = 0;
                break;
            }

            outstream->ostream.stream_errno = errno;
            if (errno != EINVAL) {
                /* close only if error wasn't because
                   sendfile() isn't supported */
                stream_closed(foutstream);
            }
            break;
        }

        v_offset += ret;
        foutstream->real_offset += ret;
        foutstream->buffer_offset += ret;
        outstream->ostream.offset += ret;
    } while ((uoff_t)ret != send_size);

    i_stream_seek(instream, v_offset);
    return ret < 0 ? -1 : (off_t)(instream->v_offset - start_offset);
}

static off_t io_stream_copy(struct ostream_private *outstream,
                struct istream *instream)
{
    struct file_ostream *foutstream = (struct file_ostream *)outstream;
    uoff_t start_offset;
    struct const_iovec iov[3];
    int iov_len;
    const unsigned char *data;
    size_t size, skip_size;
    ssize_t ret;
    int pos;

    iov_len = o_stream_fill_iovec(foutstream, iov);

        skip_size = 0;
    for (pos = 0; pos < iov_len; pos++)
        skip_size += iov[pos].iov_len;

    start_offset = instream->v_offset;
    for (;;) {
        (void)i_stream_read_data(instream, &data, &size,
                     foutstream->optimal_block_size-1);
        if (size == 0) {
            /* all sent */
            break;
        }

        pos = iov_len++;
        iov[pos].iov_base = (void *) data;
        iov[pos].iov_len = size;

        ret = o_stream_writev(foutstream, iov, iov_len);
        if (ret < 0)
            return -1;

        if (skip_size > 0) {
            if ((size_t)ret < skip_size) {
                update_buffer(foutstream, ret);
                skip_size -= ret;
                ret = 0;
            } else {
                update_buffer(foutstream, skip_size);
                ret -= skip_size;
                skip_size = 0;
            }
        }
        outstream->ostream.offset += ret;
        i_stream_skip(instream, ret);

        if ((size_t)ret != iov[pos].iov_len)
            break;

        i_assert(skip_size == 0);
        iov_len = 0;
    }

    return (off_t) (instream->v_offset - start_offset);
}

static off_t io_stream_copy_backwards(struct ostream_private *outstream,
                      struct istream *instream, uoff_t in_size)
{
    struct file_ostream *foutstream = (struct file_ostream *)outstream;
    uoff_t in_start_offset, in_offset, in_limit, out_offset;
    const unsigned char *data;
    size_t buffer_size, size, read_size;
    ssize_t ret;

    i_assert(IS_STREAM_EMPTY(foutstream));

    /* figure out optimal buffer size */
    buffer_size = instream->real_stream->buffer_size;
    if (buffer_size == 0 || buffer_size > foutstream->buffer_size) {
        if (foutstream->optimal_block_size > foutstream->buffer_size) {
            o_stream_grow_buffer(foutstream,
                         foutstream->optimal_block_size -
                         foutstream->buffer_size);
        }

        buffer_size = foutstream->buffer_size;
    }

    in_start_offset = instream->v_offset;
    in_offset = in_limit = in_size;
    out_offset = outstream->ostream.offset + (in_offset - in_start_offset);

    while (in_offset > in_start_offset) {
        if (in_offset - in_start_offset <= buffer_size)
            read_size = in_offset - in_start_offset;
        else
            read_size = buffer_size;
        in_offset -= read_size;
        out_offset -= read_size;

        for (;;) {
            i_assert(in_offset <= in_limit);

            i_stream_seek(instream, in_offset);
            read_size = in_limit - in_offset;

            (void)i_stream_read_data(instream, &data, &size,
                         read_size-1);
            if (size >= read_size) {
                size = read_size;
                if (instream->mmaped) {
                    /* we'll have to write it through
                       buffer or the file gets corrupted */
                    i_assert(size <=
                         foutstream->buffer_size);
                    memcpy(foutstream->buffer, data, size);
                    data = foutstream->buffer;
                }
                break;
            }

            /* buffer too large probably, try with smaller */
            read_size -= size;
            in_offset += read_size;
            out_offset += read_size;
            buffer_size -= read_size;
        }
        in_limit -= size;

        ret = pwrite_full(foutstream->fd, data, size, out_offset);
        if (ret < 0) {
            /* error */
            outstream->ostream.stream_errno = errno;
            return -1;
        }
    }

    return (off_t) (in_size - in_start_offset);
}

static off_t o_stream_file_send_istream(struct ostream_private *outstream,
                    struct istream *instream)
{
    struct file_ostream *foutstream = (struct file_ostream *)outstream;
    const struct stat *st;
    off_t ret;
    int in_fd;

    in_fd = i_stream_get_fd(instream);

    if (in_fd == foutstream->fd) {
        /* copying data within same fd. we'll have to be careful with
           seeks and overlapping writes. */
        st = i_stream_stat(instream, TRUE);
        if (st == NULL) {
            outstream->ostream.stream_errno = instream->stream_errno;
            return -1;
        }
        i_assert(instream->v_offset <= (uoff_t)st->st_size);

        ret = (off_t)outstream->ostream.offset -
            (off_t)(instream->real_stream->abs_start_offset +
                instream->v_offset);
        if (ret == 0) {
            /* copying data over itself. we don't really
               need to do that, just fake it. */
            return st->st_size - instream->v_offset;
        }
        if (ret > 0) {
            /* overlapping */
            return io_stream_copy_backwards(outstream, instream,
                            st->st_size);
        }
    }

    if (!foutstream->no_sendfile && in_fd != -1 && instream->seekable) {
        ret = io_stream_sendfile(outstream, instream, in_fd);
        if (ret >= 0 || outstream->ostream.stream_errno != EINVAL)
            return ret;

        /* sendfile() not supported (with this fd), fallback to
           regular sending. */
        outstream->ostream.stream_errno = 0;
        foutstream->no_sendfile = TRUE;
    }

    return io_stream_copy(outstream, instream);
}

static struct file_ostream *
o_stream_create_fd_common(int fd, bool autoclose_fd)
{
    struct file_ostream *fstream;

    fstream = i_new(struct file_ostream, 1);
    fstream->fd = fd;
    fstream->autoclose_fd = autoclose_fd;
    fstream->optimal_block_size = DEFAULT_OPTIMAL_BLOCK_SIZE;

    fstream->ostream.iostream.close = o_stream_file_close;
    fstream->ostream.iostream.destroy = o_stream_file_destroy;
    fstream->ostream.iostream.set_max_buffer_size =
        o_stream_file_set_max_buffer_size;

    fstream->ostream.cork = o_stream_file_cork;
    fstream->ostream.flush = o_stream_file_flush;
    fstream->ostream.flush_pending = o_stream_file_flush_pending;
    fstream->ostream.get_used_size = o_stream_file_get_used_size;
    fstream->ostream.seek = o_stream_file_seek;
    fstream->ostream.sendv = o_stream_file_sendv;
    fstream->ostream.send_istream = o_stream_file_send_istream;

    return fstream;
}

static void fstream_init_file(struct file_ostream *fstream)
{
    struct stat st;

    fstream->no_sendfile = TRUE;
    if (fstat(fstream->fd, &st) < 0)
        return;

    if ((uoff_t)st.st_blksize > fstream->optimal_block_size) {
        /* use the optimal block size, but with a reasonable limit */
        fstream->optimal_block_size =
            I_MIN(st.st_blksize, MAX_OPTIMAL_BLOCK_SIZE);
    }

    if (S_ISREG(st.st_mode)) {
        fstream->no_socket_cork = TRUE;
        fstream->file = TRUE;
    }
}

struct ostream *
o_stream_create_fd(int fd, size_t max_buffer_size, bool autoclose_fd)
{
    struct file_ostream *fstream;
    struct ostream *ostream;
    off_t offset;

    fstream = o_stream_create_fd_common(fd, autoclose_fd);
    fstream->max_buffer_size = max_buffer_size;
    ostream = o_stream_create(&fstream->ostream);

    offset = lseek(fd, 0, SEEK_CUR);
    if (offset >= 0) {
        ostream->offset = offset;
        fstream->real_offset = offset;
        fstream->buffer_offset = offset;
        fstream_init_file(fstream);
    } else {
        if (net_getsockname(fd, NULL, NULL) < 0) {
            fstream->no_sendfile = TRUE;
            fstream->no_socket_cork = TRUE;
        }
    }

    if (max_buffer_size == 0)
        fstream->max_buffer_size = fstream->optimal_block_size;

    return ostream;
}

struct ostream *
o_stream_create_fd_file(int fd, uoff_t offset, bool autoclose_fd)
{
    struct file_ostream *fstream;
    struct ostream *ostream;

    if (offset == (uoff_t)-1)
        offset = lseek(fd, 0, SEEK_CUR);

    fstream = o_stream_create_fd_common(fd, autoclose_fd);
    fstream_init_file(fstream);
    fstream->max_buffer_size = fstream->optimal_block_size;
    fstream->real_offset = offset;
    fstream->buffer_offset = offset;

    ostream = o_stream_create(&fstream->ostream);
    ostream->offset = offset;
    return ostream;
}