istream-mmap.c revision 8cb72c59d5ea4e9e5f638d7ec840bb853f5a188e
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen/* Copyright (c) 2002-2010 Dovecot authors, see the included COPYING file */
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen#include "lib.h"
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen#include "ioloop.h"
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen#include "mmap-util.h"
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen#include "istream-internal.h"
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen#include <unistd.h>
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen#include <sys/stat.h>
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainenstruct mmap_istream {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen struct istream_private istream;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen struct timeval fstat_cache_stamp;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen void *mmap_base;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen off_t mmap_offset;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen uoff_t v_size;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen unsigned int autoclose_fd:1;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen};
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainenstatic size_t mmap_pagemask = 0;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainenstatic void i_stream_mmap_close(struct iostream_private *stream)
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen{
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen struct mmap_istream *mstream = (struct mmap_istream *) stream;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (mstream->autoclose_fd && mstream->istream.fd != -1) {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (close(mstream->istream.fd) < 0) {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_error("mmap_istream.close(%s) failed: %m",
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_stream_get_name(&mstream->istream.istream));
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen }
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen }
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen mstream->istream.fd = -1;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen}
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainenstatic void i_stream_munmap(struct mmap_istream *mstream)
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen{
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen struct istream_private *_stream = &mstream->istream;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (_stream->buffer != NULL) {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (munmap(mstream->mmap_base, _stream->buffer_size) < 0) {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_error("mmap_istream.munmap(%s) failed: %m",
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_stream_get_name(&_stream->istream));
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen }
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen mstream->mmap_base = NULL;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen _stream->buffer = NULL;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen _stream->buffer_size = 0;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen mstream->mmap_offset = 0;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen }
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen}
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainenstatic void i_stream_mmap_destroy(struct iostream_private *stream)
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen{
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen struct mmap_istream *mstream = (struct mmap_istream *) stream;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_stream_munmap(mstream);
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen}
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainenstatic size_t mstream_get_mmap_block_size(struct istream_private *stream)
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen{
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen return (stream->max_buffer_size + mmap_get_page_size() - 1) & ~
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen (mmap_get_page_size() - 1);
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen}
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainenstatic ssize_t i_stream_mmap_read(struct istream_private *stream)
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen{
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen struct mmap_istream *mstream = (struct mmap_istream *) stream;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen size_t aligned_skip;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen uoff_t top;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (stream->pos < stream->buffer_size) {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen /* more bytes available without needing to mmap() */
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen stream->pos = stream->buffer_size;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen return stream->pos - stream->skip;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen }
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (stream->istream.v_offset >= mstream->v_size) {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen stream->istream.eof = TRUE;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen return -1;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen }
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen aligned_skip = stream->skip & ~mmap_pagemask;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (aligned_skip == 0 && mstream->mmap_base != NULL) {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen /* didn't skip enough bytes */
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen return -2;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen }
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen stream->skip -= aligned_skip;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen mstream->mmap_offset += aligned_skip;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (mstream->mmap_base != NULL) {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (munmap(mstream->mmap_base, stream->buffer_size) < 0) {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_error("mmap_istream.munmap(%s) failed: %m",
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_stream_get_name(&stream->istream));
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen }
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen }
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen top = mstream->v_size - mstream->mmap_offset;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen stream->buffer_size = I_MIN(top, mstream_get_mmap_block_size(stream));
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_assert((uoff_t)mstream->mmap_offset + stream->buffer_size <=
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen mstream->v_size);
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (stream->buffer_size == 0) {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen /* don't bother even trying mmap */
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen mstream->mmap_base = NULL;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen stream->buffer = NULL;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen } else {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen mstream->mmap_base =
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen mmap(NULL, stream->buffer_size, PROT_READ, MAP_PRIVATE,
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen stream->fd, mstream->mmap_offset);
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (mstream->mmap_base == MAP_FAILED) {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_assert(errno != 0);
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen stream->istream.stream_errno = errno;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen mstream->mmap_base = NULL;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen stream->buffer = NULL;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen stream->buffer_size = 0;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen stream->skip = stream->pos = 0;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_error("mmap_istream.mmap(%s) failed: %m",
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_stream_get_name(&stream->istream));
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen return -1;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen }
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen stream->buffer = mstream->mmap_base;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen }
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (stream->buffer_size > mmap_get_page_size()) {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (madvise(mstream->mmap_base, stream->buffer_size,
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen MADV_SEQUENTIAL) < 0) {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_error("mmap_istream.madvise(%s): %m",
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_stream_get_name(&stream->istream));
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen }
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen }
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen stream->pos = stream->buffer_size;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_assert(stream->pos - stream->skip > 0);
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen return stream->pos - stream->skip;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen}
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainenstatic void i_stream_mmap_seek(struct istream_private *stream, uoff_t v_offset,
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen bool mark ATTR_UNUSED)
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen{
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen struct mmap_istream *mstream = (struct mmap_istream *) stream;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (stream->buffer_size != 0 &&
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen (uoff_t)mstream->mmap_offset <= v_offset &&
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen (uoff_t)mstream->mmap_offset + stream->buffer_size > v_offset) {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen /* already mmaped */
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen stream->skip = stream->pos = v_offset - mstream->mmap_offset;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen } else {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen /* force reading next time */
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_stream_munmap(mstream);
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen stream->skip = stream->pos = v_offset;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen }
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen stream->istream.v_offset = v_offset;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen}
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainenstatic void i_stream_mmap_sync(struct istream_private *stream)
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen{
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen struct mmap_istream *mstream = (struct mmap_istream *) stream;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_stream_munmap(mstream);
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen stream->skip = stream->pos = stream->istream.v_offset;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen mstream->fstat_cache_stamp.tv_sec = 0;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen}
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainenstatic int fstat_cached(struct mmap_istream *mstream)
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen{
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (mstream->fstat_cache_stamp.tv_sec == ioloop_timeval.tv_sec &&
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen mstream->fstat_cache_stamp.tv_usec == ioloop_timeval.tv_usec)
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen return 0;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (fstat(mstream->istream.fd, &mstream->istream.statbuf) < 0) {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_error("mmap_istream.fstat(%s) failed: %m",
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_stream_get_name(&mstream->istream.istream));
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen return -1;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen }
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen mstream->fstat_cache_stamp = ioloop_timeval;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen return 0;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen}
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainenstatic const struct stat *
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Siraineni_stream_mmap_stat(struct istream_private *stream, bool exact ATTR_UNUSED)
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen{
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen struct mmap_istream *mstream = (struct mmap_istream *) stream;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (fstat_cached(mstream) < 0)
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen return NULL;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen return &stream->statbuf;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen}
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainenstruct istream *i_stream_create_mmap(int fd, size_t block_size,
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen uoff_t start_offset, uoff_t v_size,
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen bool autoclose_fd)
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen{
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen struct mmap_istream *mstream;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen struct istream *istream;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen struct stat st;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (mmap_pagemask == 0)
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen mmap_pagemask = mmap_get_page_size()-1;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (v_size == 0) {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (fstat(fd, &st) < 0)
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen i_error("i_stream_create_mmap(): fstat() failed: %m");
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen else {
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen v_size = st.st_size;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen if (start_offset > v_size)
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen start_offset = v_size;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen v_size -= start_offset;
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen }
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen }
1537d20b852cbbf0d6971790b84e0cce5ca61307Timo Sirainen
mstream = i_new(struct mmap_istream, 1);
mstream->autoclose_fd = autoclose_fd;
mstream->v_size = v_size;
mstream->istream.iostream.close = i_stream_mmap_close;
mstream->istream.iostream.destroy = i_stream_mmap_destroy;
mstream->istream.max_buffer_size = block_size;
mstream->istream.read = i_stream_mmap_read;
mstream->istream.seek = i_stream_mmap_seek;
mstream->istream.sync = i_stream_mmap_sync;
mstream->istream.stat = i_stream_mmap_stat;
mstream->istream.istream.readable_fd = TRUE;
mstream->istream.abs_start_offset = start_offset;
istream = i_stream_create(&mstream->istream, NULL, fd);
istream->mmaped = TRUE;
istream->blocking = TRUE;
istream->seekable = TRUE;
return istream;
}