src/lib/file-cache.c

	file-cache.c revision 77717f1e9e8442fd2cdbca87cbc45c03d0b5fcae
/* Copyright (c) 2004 Timo Sirainen */

#include "lib.h"
#include "buffer.h"
#include "mmap-util.h"
#include "file-cache.h"

#include <sys/stat.h>

struct file_cache {
    int fd;
    buffer_t *page_bitmask;

    void *mmap_base;
    size_t mmap_length;
    size_t read_highwater;
};

struct file_cache *file_cache_new(int fd)
{
    struct file_cache *cache;

    cache = i_new(struct file_cache, 1);
    cache->fd = fd;
    cache->page_bitmask = buffer_create_dynamic(default_pool, 128);
    return cache;
}

void file_cache_free(struct file_cache *cache)
{
    if (cache->mmap_base != NULL) {
        if (munmap_anon(cache->mmap_base, cache->mmap_length) < 0)
            i_error("munmap_anon() failed: %m");
    }
    buffer_free(cache->page_bitmask);
    i_free(cache);
}

void file_cache_set_fd(struct file_cache *cache, int fd)
{
    cache->fd = fd;
    file_cache_invalidate(cache, 0, cache->mmap_length);
}

ssize_t file_cache_read(struct file_cache *cache, uoff_t offset, size_t size)
{
    size_t page_size = mmap_get_page_size();
    size_t poffset, psize, mmap_needed, dest_offset, dest_size;
    unsigned char *bits, *dest;
    ssize_t ret;

    if (size > SSIZE_T_MAX) {
        /* make sure our calculations won't overflow. most likely
           we'll be reading less data, but allow it anyway so caller
           doesn't have to deal with any extra checks. */
        size = SSIZE_T_MAX;
    }

    if (offset + size > cache->mmap_length &&
        offset + size - cache->mmap_length > 1024*1024) {
        /* growing more than a megabyte, make sure that the
           file is large enough so we don't allocate memory
           more than needed */
        struct stat st;

        if (fstat(cache->fd, &st) < 0) {
            i_error("fstat(file_cache) failed: %m");
            return -1;
        }

        if (offset + size > (uoff_t)st.st_size) {
            if (offset >= (uoff_t)st.st_size)
                return 0;
            size = (uoff_t)st.st_size - offset;
        }
    }

    poffset = offset / page_size;
    psize = (offset + size + page_size-1) / page_size - poffset;
    i_assert(psize > 0);

    mmap_needed = (poffset + psize) * page_size;
    if (mmap_needed > cache->mmap_length) {
        /* grow mmaping */
        if (cache->mmap_base == NULL) {
            cache->mmap_base = mmap_anon(mmap_needed);
            if (cache->mmap_base == MAP_FAILED) {
                i_error("mmap_anon(%"PRIuSIZE_T") failed: %m",
                    mmap_needed);
                return -1;
            }
        } else {
            cache->mmap_base = mremap_anon(cache->mmap_base,
                               cache->mmap_length,
                               mmap_needed,
                               MREMAP_MAYMOVE);
            if (cache->mmap_base == MAP_FAILED) {
                i_error("mremap_anon(%"PRIuSIZE_T") failed: %m",
                    mmap_needed);
                return -1;
            }
        }
        cache->mmap_length = mmap_needed;
    }

    bits = buffer_get_space_unsafe(cache->page_bitmask, 0,
                       poffset / CHAR_BIT +
                       (psize + CHAR_BIT - 1) / CHAR_BIT);

    dest_offset = poffset * page_size;
    dest = PTR_OFFSET(cache->mmap_base, dest_offset);
    dest_size = page_size;

    while (psize > 0) {
        if (bits[poffset / CHAR_BIT] & (1 << (poffset % CHAR_BIT))) {
            /* page is already in cache */
            psize--; poffset++;
            dest += page_size;
            dest_offset += page_size;
            continue;
        }

        ret = pread(cache->fd, dest, dest_size, dest_offset);
        if (ret <= 0) {
            if (ret < 0)
                return -1;

            /* EOF */
            /* FIXME: we should mark the last block cached and
               invalidate it only when trying to read past the
               file */
            return dest_offset <= offset ? 0 :
                dest_offset - offset < size ?
                dest_offset - offset : size;
        }

        dest += ret;
        dest_offset += ret;

        if (cache->read_highwater < dest_offset)
            cache->read_highwater = dest_offset;

        if ((size_t)ret != dest_size) {
            /* partial read - probably EOF but make sure. */
            dest_size -= ret;
            continue;
        }

        bits[poffset / CHAR_BIT] |= 1 << (poffset % CHAR_BIT);
        dest_size = page_size;
        psize--; poffset++;
    }

    return size;
}

const void *file_cache_get_map(struct file_cache *cache, size_t *size_r)
{
    *size_r = cache->read_highwater;
    return cache->mmap_base;
}

void file_cache_invalidate(struct file_cache *cache, uoff_t offset, uoff_t size)
{
    size_t page_size = mmap_get_page_size();
    unsigned char *bits, mask;
    unsigned int i;

    if (offset >= cache->read_highwater)
        return;

    if (size > cache->read_highwater - offset)
        size = cache->read_highwater - offset;

    size = (offset + size + page_size-1) / page_size;
    offset /= page_size;
    size -= offset;

    if (size != 1) {
        /* tell operating system that we don't need the memory anymore
           and it may free it. don't bother to do it for single pages,
           there's a good chance that they get re-read back
           immediately. */
        (void)madvise(PTR_OFFSET(cache->mmap_base, offset * page_size),
                  size * page_size, MADV_DONTNEED);
    }

    bits = buffer_get_space_unsafe(cache->page_bitmask, offset / CHAR_BIT,
                       (size + CHAR_BIT - 1) / CHAR_BIT);

    /* set the first byte */
    for (i = offset % CHAR_BIT, mask = 0; i < CHAR_BIT && size > 0; i++) {
        mask |= 1 << i;
        size--;
    }
    *bits++ &= ~mask;

    /* set the middle bytes */
    memset(bits, 0, size / CHAR_BIT);
    bits += size / CHAR_BIT;
    size %= CHAR_BIT;

    /* set the last byte */
    if (size > 0) {
        mask = 0;
        for (i = 0, mask = 0; i < size; i++)
            mask |= 1 << i;
        *bits &= ~mask;
    }
}