/*
   istream-mmap.c : Input stream handling for mmap()ed files

    Copyright (c) 2002 Timo Sirainen

    Permission is hereby granted, free of charge, to any person obtaining
    a copy of this software and associated documentation files (the
    "Software"), to deal in the Software without restriction, including
    without limitation the rights to use, copy, modify, merge, publish,
    distribute, sublicense, and/or sell copies of the Software, and to
    permit persons to whom the Software is furnished to do so, subject to
    the following conditions:

    The above copyright notice and this permission notice shall be
    included in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
    OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
    IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
    CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
    TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
    SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

#include "lib.h"
#include "mmap-util.h"
#include "istream-internal.h"

#include <unistd.h>
#include <sys/stat.h>

struct mmap_istream {
	struct _istream istream;

	int fd;
	void *mmap_base;
	off_t mmap_offset;
	size_t mmap_block_size;

	unsigned int autoclose_fd:1;
};

static size_t mmap_pagesize = 0;
static size_t mmap_pagemask = 0;

static void _close(struct _iostream *stream)
{
	struct mmap_istream *mstream = (struct mmap_istream *) stream;

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

static void i_stream_munmap(struct mmap_istream *mstream)
{
	struct _istream *_stream = &mstream->istream;

	if (_stream->buffer != NULL) {
		if (munmap(mstream->mmap_base, _stream->buffer_size) < 0)
			i_error("mmap_istream.munmap() failed: %m");
		mstream->mmap_base = NULL;
		_stream->buffer = NULL;
		_stream->buffer_size = 0;
		mstream->mmap_offset = 0;
	}
}

static void _destroy(struct _iostream *stream)
{
	struct mmap_istream *mstream = (struct mmap_istream *) stream;

	i_stream_munmap(mstream);
}

static void _set_max_buffer_size(struct _iostream *stream, size_t max_size)
{
	struct mmap_istream *mstream = (struct mmap_istream *) stream;

	/* allow only full page sizes */
	if (max_size < mmap_pagesize)
		mstream->mmap_block_size = mmap_pagesize;
	else {
		if (max_size % mmap_pagesize != 0)
			max_size += mmap_pagesize - (max_size % mmap_pagesize);
		mstream->mmap_block_size = max_size;
	}
}

static void _set_blocking(struct _iostream *stream __attr_unused__,
			  int timeout_msecs __attr_unused__,
			  void (*timeout_cb)(void *) __attr_unused__,
			  void *context __attr_unused__)
{
	/* we never block */
}

static ssize_t io_stream_set_mmaped_pos(struct _istream *stream)
{
	struct mmap_istream *mstream = (struct mmap_istream *) stream;
	uoff_t top;

	i_assert((uoff_t)mstream->mmap_offset <=
		 stream->istream.start_offset + stream->istream.v_limit);

	top = stream->istream.start_offset + stream->istream.v_limit -
		mstream->mmap_offset;
	stream->pos = I_MIN(top, stream->buffer_size);

	return stream->pos - stream->skip;
}

static ssize_t _read(struct _istream *stream)
{
	struct mmap_istream *mstream = (struct mmap_istream *) stream;
	size_t aligned_skip, limit_size;
	uoff_t top;

	if (stream->istream.start_offset + stream->istream.v_limit <=
	    (uoff_t)mstream->mmap_offset + stream->pos) {
		/* end of file */
		stream->istream.stream_errno = 0;
		return -1;
	}

	if (stream->pos < stream->buffer_size) {
		/* more bytes available without needing to mmap() */
		return io_stream_set_mmaped_pos(stream);
	}

	aligned_skip = stream->skip & ~mmap_pagemask;
	if (aligned_skip == 0 && mstream->mmap_base != NULL) {
		/* didn't skip enough bytes */
		return -2;
	}

	stream->skip -= aligned_skip;
	mstream->mmap_offset += aligned_skip;

	if (mstream->mmap_base != NULL) {
		if (munmap(mstream->mmap_base, stream->buffer_size) < 0)
			i_error("io_stream_read_mmaped(): munmap() failed: %m");
	}

	top = stream->istream.start_offset + stream->istream.v_size -
		mstream->mmap_offset;
	stream->buffer_size = I_MIN(top, mstream->mmap_block_size);

	i_assert((uoff_t)mstream->mmap_offset + stream->buffer_size <=
		 stream->istream.start_offset + stream->istream.v_size);

	mstream->mmap_base = mmap(NULL, stream->buffer_size,
				  PROT_READ, MAP_PRIVATE,
				  mstream->fd, mstream->mmap_offset);
	if (mstream->mmap_base == MAP_FAILED) {
		stream->istream.stream_errno = errno;
		mstream->mmap_base = NULL;
		stream->buffer = NULL;
		stream->buffer_size = 0;
		stream->skip = stream->pos = 0;
		i_error("mmap_istream.mmap() failed: %m");
		return -1;
	}
	stream->buffer = mstream->mmap_base;

	/* madvise() only if non-limited mmap()ed buffer area larger than
	   page size */
	limit_size = stream->istream.start_offset + stream->istream.v_limit -
		mstream->mmap_offset;
	if (limit_size > mmap_pagesize) {
		if (limit_size > stream->buffer_size)
			limit_size = stream->buffer_size;

		if (madvise(mstream->mmap_base, limit_size,
			    MADV_SEQUENTIAL) < 0)
			i_error("mmap_istream.madvise(): %m");
	}

	return io_stream_set_mmaped_pos(stream);
}

static void _seek(struct _istream *stream, uoff_t v_offset)
{
	struct mmap_istream *mstream = (struct mmap_istream *) stream;
	uoff_t abs_offset;

	abs_offset = stream->istream.start_offset + v_offset;
	if (stream->buffer_size != 0 &&
	    (uoff_t)mstream->mmap_offset <= abs_offset &&
	    (uoff_t)mstream->mmap_offset + stream->buffer_size > abs_offset) {
		/* already mmaped */
		stream->skip = stream->pos = abs_offset - mstream->mmap_offset;
	} else {
		/* force reading next time */
		i_stream_munmap(mstream);
		stream->skip = stream->pos = abs_offset;
	}

	stream->istream.v_offset = v_offset;
}

static void _skip(struct _istream *stream, uoff_t count)
{
	_seek(stream, stream->istream.v_offset + count);
}

struct istream *i_stream_create_mmap(int fd, pool_t pool, size_t block_size,
				     uoff_t start_offset, uoff_t v_size,
				     int autoclose_fd)
{
	struct mmap_istream *mstream;
        struct istream *istream;
	struct stat st;

	if (mmap_pagesize == 0) {
		mmap_pagesize = getpagesize();
		mmap_pagemask = mmap_pagesize-1;
	}

	if (v_size == 0) {
		if (fstat(fd, &st) < 0) {
			i_error("i_stream_create_mmap(): fstat() failed: %m");
			v_size = 0;
		} else {
			v_size = st.st_size;
			if (start_offset > v_size)
				start_offset = v_size;
			v_size -= start_offset;
		}
	}

	mstream = p_new(pool, struct mmap_istream, 1);
	mstream->fd = fd;
        _set_max_buffer_size(&mstream->istream.iostream, block_size);
	mstream->autoclose_fd = autoclose_fd;

	mstream->istream.iostream.close = _close;
	mstream->istream.iostream.destroy = _destroy;
	mstream->istream.iostream.set_max_buffer_size = _set_max_buffer_size;
	mstream->istream.iostream.set_blocking = _set_blocking;

	mstream->istream.read = _read;
	mstream->istream.skip_count = _skip;
	mstream->istream.seek = _seek;

	istream = _i_stream_create(&mstream->istream, pool, fd,
				   start_offset, v_size);
	istream->mmaped = TRUE;
	return istream;
}