file.c

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/*
 * Squashfs - a compressed read only filesystem for Linux
 *
 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
 * Phillip Lougher <[email protected]>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2,
 * or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * file.c
 */

/*
 * This file contains code for handling regular files.  A regular file
 * consists of a sequence of contiguous compressed blocks, and/or a
 * compressed fragment block (tail-end packed block).   The compressed size
 * of each datablock is stored in a block list contained within the
 * file inode (itself stored in one or more compressed metadata blocks).
 *
 * To speed up access to datablocks when reading 'large' files (256 Mbytes or
 * larger), the code implements an index cache that caches the mapping from
 * block index to datablock location on disk.
 *
 * The index cache allows Squashfs to handle large files (up to 1.75 TiB) while
 * retaining a simple and space-efficient block list on disk.  The cache
 * is split into slots, caching up to eight 224 GiB files (128 KiB blocks).
 * Larger files use multiple slots, with 1.75 TiB files using all 8 slots.
 * The index cache is designed to be memory efficient, and by default uses
 * 16 KiB.
 */

#include <linux/fs.h>
#include <linux/vfs.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/pagemap.h>
#include <linux/mutex.h>

#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "squashfs_fs_i.h"
#include "squashfs.h"

/*
 * Locate cache slot in range [offset, index] for specified inode.  If
 * there's more than one return the slot closest to index.
 */
static struct meta_index *locate_meta_index(struct inode *inode, int offset,
                int index)
{
    struct meta_index *meta = NULL;
    struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
    int i;

    mutex_lock(&msblk->meta_index_mutex);

    TRACE("locate_meta_index: index %d, offset %d\n", index, offset);

    if (msblk->meta_index == NULL)
        goto not_allocated;

    for (i = 0; i < SQUASHFS_META_SLOTS; i++) {
        if (msblk->meta_index[i].inode_number == inode->i_ino &&
                msblk->meta_index[i].offset >= offset &&
                msblk->meta_index[i].offset <= index &&
                msblk->meta_index[i].locked == 0) {
            TRACE("locate_meta_index: entry %d, offset %d\n", i,
                    msblk->meta_index[i].offset);
            meta = &msblk->meta_index[i];
            offset = meta->offset;
        }
    }

    if (meta)
        meta->locked = 1;

not_allocated:
    mutex_unlock(&msblk->meta_index_mutex);

    return meta;
}


/*
 * Find and initialise an empty cache slot for index offset.
 */
static struct meta_index *empty_meta_index(struct inode *inode, int offset,
                int skip)
{
    struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
    struct meta_index *meta = NULL;
    int i;

    mutex_lock(&msblk->meta_index_mutex);

    TRACE("empty_meta_index: offset %d, skip %d\n", offset, skip);

    if (msblk->meta_index == NULL) {
        /*
         * First time cache index has been used, allocate and
         * initialise.  The cache index could be allocated at
         * mount time but doing it here means it is allocated only
         * if a 'large' file is read.
         */
        msblk->meta_index = kcalloc(SQUASHFS_META_SLOTS,
            sizeof(*(msblk->meta_index)), GFP_KERNEL);
        if (msblk->meta_index == NULL) {
            ERROR("Failed to allocate meta_index\n");
            goto failed;
        }
        for (i = 0; i < SQUASHFS_META_SLOTS; i++) {
            msblk->meta_index[i].inode_number = 0;
            msblk->meta_index[i].locked = 0;
        }
        msblk->next_meta_index = 0;
    }

    for (i = SQUASHFS_META_SLOTS; i &&
            msblk->meta_index[msblk->next_meta_index].locked; i--)
        msblk->next_meta_index = (msblk->next_meta_index + 1) %
            SQUASHFS_META_SLOTS;

    if (i == 0) {
        TRACE("empty_meta_index: failed!\n");
        goto failed;
    }

    TRACE("empty_meta_index: returned meta entry %d, %p\n",
            msblk->next_meta_index,
            &msblk->meta_index[msblk->next_meta_index]);

    meta = &msblk->meta_index[msblk->next_meta_index];
    msblk->next_meta_index = (msblk->next_meta_index + 1) %
            SQUASHFS_META_SLOTS;

    meta->inode_number = inode->i_ino;
    meta->offset = offset;
    meta->skip = skip;
    meta->entries = 0;
    meta->locked = 1;

failed:
    mutex_unlock(&msblk->meta_index_mutex);
    return meta;
}


static void release_meta_index(struct inode *inode, struct meta_index *meta)
{
    struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
    mutex_lock(&msblk->meta_index_mutex);
    meta->locked = 0;
    mutex_unlock(&msblk->meta_index_mutex);
}


/*
 * Read the next n blocks from the block list, starting from
 * metadata block <start_block, offset>.
 */
static long long read_indexes(struct super_block *sb, int n,
                u64 *start_block, int *offset)
{
    int err, i;
    long long block = 0;
    __le32 *blist = kmalloc(PAGE_CACHE_SIZE, GFP_KERNEL);

    if (blist == NULL) {
        ERROR("read_indexes: Failed to allocate block_list\n");
        return -ENOMEM;
    }

    while (n) {
        int blocks = min_t(int, n, PAGE_CACHE_SIZE >> 2);

        err = squashfs_read_metadata(sb, blist, start_block,
                offset, blocks << 2);
        if (err < 0) {
            ERROR("read_indexes: reading block [%llx:%x]\n",
                *start_block, *offset);
            goto failure;
        }

        for (i = 0; i < blocks; i++) {
            int size = le32_to_cpu(blist[i]);
            block += SQUASHFS_COMPRESSED_SIZE_BLOCK(size);
        }
        n -= blocks;
    }

    kfree(blist);
    return block;

failure:
    kfree(blist);
    return err;
}


/*
 * Each cache index slot has SQUASHFS_META_ENTRIES, each of which
 * can cache one index -> datablock/blocklist-block mapping.  We wish
 * to distribute these over the length of the file, entry[0] maps index x,
 * entry[1] maps index x + skip, entry[2] maps index x + 2 * skip, and so on.
 * The larger the file, the greater the skip factor.  The skip factor is
 * limited to the size of the metadata cache (SQUASHFS_CACHED_BLKS) to ensure
 * the number of metadata blocks that need to be read fits into the cache.
 * If the skip factor is limited in this way then the file will use multiple
 * slots.
 */
static inline int calculate_skip(int blocks)
{
    int skip = blocks / ((SQUASHFS_META_ENTRIES + 1)
         * SQUASHFS_META_INDEXES);
    return min(SQUASHFS_CACHED_BLKS - 1, skip + 1);
}


/*
 * Search and grow the index cache for the specified inode, returning the
 * on-disk locations of the datablock and block list metadata block
 * <index_block, index_offset> for index (scaled to nearest cache index).
 */
static int fill_meta_index(struct inode *inode, int index,
        u64 *index_block, int *index_offset, u64 *data_block)
{
    struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
    int skip = calculate_skip(i_size_read(inode) >> msblk->block_log);
    int offset = 0;
    struct meta_index *meta;
    struct meta_entry *meta_entry;
    u64 cur_index_block = squashfs_i(inode)->block_list_start;
    int cur_offset = squashfs_i(inode)->offset;
    u64 cur_data_block = squashfs_i(inode)->start;
    int err, i;

    /*
     * Scale index to cache index (cache slot entry)
     */
    index /= SQUASHFS_META_INDEXES * skip;

    while (offset < index) {
        meta = locate_meta_index(inode, offset + 1, index);

        if (meta == NULL) {
            meta = empty_meta_index(inode, offset + 1, skip);
            if (meta == NULL)
                goto all_done;
        } else {
            offset = index < meta->offset + meta->entries ? index :
                meta->offset + meta->entries - 1;
            meta_entry = &meta->meta_entry[offset - meta->offset];
            cur_index_block = meta_entry->index_block +
                msblk->inode_table;
            cur_offset = meta_entry->offset;
            cur_data_block = meta_entry->data_block;
            TRACE("get_meta_index: offset %d, meta->offset %d, "
                "meta->entries %d\n", offset, meta->offset,
                meta->entries);
            TRACE("get_meta_index: index_block 0x%llx, offset 0x%x"
                " data_block 0x%llx\n", cur_index_block,
                cur_offset, cur_data_block);
        }

        /*
         * If necessary grow cache slot by reading block list.  Cache
         * slot is extended up to index or to the end of the slot, in
         * which case further slots will be used.
         */
        for (i = meta->offset + meta->entries; i <= index &&
                i < meta->offset + SQUASHFS_META_ENTRIES; i++) {
            int blocks = skip * SQUASHFS_META_INDEXES;
            long long res = read_indexes(inode->i_sb, blocks,
                    &cur_index_block, &cur_offset);

            if (res < 0) {
                if (meta->entries == 0)
                    /*
                     * Don't leave an empty slot on read
                     * error allocated to this inode...
                     */
                    meta->inode_number = 0;
                err = res;
                goto failed;
            }

            cur_data_block += res;
            meta_entry = &meta->meta_entry[i - meta->offset];
            meta_entry->index_block = cur_index_block -
                msblk->inode_table;
            meta_entry->offset = cur_offset;
            meta_entry->data_block = cur_data_block;
            meta->entries++;
            offset++;
        }

        TRACE("get_meta_index: meta->offset %d, meta->entries %d\n",
                meta->offset, meta->entries);

        release_meta_index(inode, meta);
    }

all_done:
    *index_block = cur_index_block;
    *index_offset = cur_offset;
    *data_block = cur_data_block;

    /*
     * Scale cache index (cache slot entry) to index
     */
    return offset * SQUASHFS_META_INDEXES * skip;

failed:
    release_meta_index(inode, meta);
    return err;
}


/*
 * Get the on-disk location and compressed size of the datablock
 * specified by index.  Fill_meta_index() does most of the work.
 */
static int read_blocklist(struct inode *inode, int index, u64 *block)
{
    u64 start;
    long long blks;
    int offset;
    __le32 size;
    int res = fill_meta_index(inode, index, &start, &offset, block);

    TRACE("read_blocklist: res %d, index %d, start 0x%llx, offset"
               " 0x%x, block 0x%llx\n", res, index, start, offset,
            *block);

    if (res < 0)
        return res;

    /*
     * res contains the index of the mapping returned by fill_meta_index(),
     * this will likely be less than the desired index (because the
     * meta_index cache works at a higher granularity).  Read any
     * extra block indexes needed.
     */
    if (res < index) {
        blks = read_indexes(inode->i_sb, index - res, &start, &offset);
        if (blks < 0)
            return (int) blks;
        *block += blks;
    }

    /*
     * Read length of block specified by index.
     */
    res = squashfs_read_metadata(inode->i_sb, &size, &start, &offset,
            sizeof(size));
    if (res < 0)
        return res;
    return le32_to_cpu(size);
}


static int squashfs_readpage(struct file *file, struct page *page)
{
    struct inode *inode = page->mapping->host;
    struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
    int bytes, i, offset = 0, sparse = 0;
    struct squashfs_cache_entry *buffer = NULL;
    void *pageaddr;

    int mask = (1 << (msblk->block_log - PAGE_CACHE_SHIFT)) - 1;
    int index = page->index >> (msblk->block_log - PAGE_CACHE_SHIFT);
    int start_index = page->index & ~mask;
    int end_index = start_index | mask;
    int file_end = i_size_read(inode) >> msblk->block_log;

    TRACE("Entered squashfs_readpage, page index %lx, start block %llx\n",
                page->index, squashfs_i(inode)->start);

    if (page->index >= ((i_size_read(inode) + PAGE_CACHE_SIZE - 1) >>
                    PAGE_CACHE_SHIFT))
        goto out;

    if (index < file_end || squashfs_i(inode)->fragment_block ==
                    SQUASHFS_INVALID_BLK) {
        /*
         * Reading a datablock from disk.  Need to read block list
         * to get location and block size.
         */
        u64 block = 0;
        int bsize = read_blocklist(inode, index, &block);
        if (bsize < 0)
            goto error_out;

        if (bsize == 0) { /* hole */
            bytes = index == file_end ?
                (i_size_read(inode) & (msblk->block_size - 1)) :
                 msblk->block_size;
            sparse = 1;
        } else {
            /*
             * Read and decompress datablock.
             */
            buffer = squashfs_get_datablock(inode->i_sb,
                                block, bsize);
            if (buffer->error) {
                ERROR("Unable to read page, block %llx, size %x"
                    "\n", block, bsize);
                squashfs_cache_put(buffer);
                goto error_out;
            }
            bytes = buffer->length;
        }
    } else {
        /*
         * Datablock is stored inside a fragment (tail-end packed
         * block).
         */
        buffer = squashfs_get_fragment(inode->i_sb,
                squashfs_i(inode)->fragment_block,
                squashfs_i(inode)->fragment_size);

        if (buffer->error) {
            ERROR("Unable to read page, block %llx, size %x\n",
                squashfs_i(inode)->fragment_block,
                squashfs_i(inode)->fragment_size);
            squashfs_cache_put(buffer);
            goto error_out;
        }
        bytes = i_size_read(inode) & (msblk->block_size - 1);
        offset = squashfs_i(inode)->fragment_offset;
    }

    /*
     * Loop copying datablock into pages.  As the datablock likely covers
     * many PAGE_CACHE_SIZE pages (default block size is 128 KiB) explicitly
     * grab the pages from the page cache, except for the page that we've
     * been called to fill.
     */
    for (i = start_index; i <= end_index && bytes > 0; i++,
            bytes -= PAGE_CACHE_SIZE, offset += PAGE_CACHE_SIZE) {
        struct page *push_page;
        int avail = sparse ? 0 : min_t(int, bytes, PAGE_CACHE_SIZE);

        TRACE("bytes %d, i %d, available_bytes %d\n", bytes, i, avail);

        push_page = (i == page->index) ? page :
            grab_cache_page_nowait(page->mapping, i);

        if (!push_page)
            continue;

        if (PageUptodate(push_page))
            goto skip_page;

        pageaddr = kmap_atomic(push_page);
        squashfs_copy_data(pageaddr, buffer, offset, avail);
        memset(pageaddr + avail, 0, PAGE_CACHE_SIZE - avail);
        kunmap_atomic(pageaddr);
        flush_dcache_page(push_page);
        SetPageUptodate(push_page);
skip_page:
        unlock_page(push_page);
        if (i != page->index)
            page_cache_release(push_page);
    }

    if (!sparse)
        squashfs_cache_put(buffer);

    return 0;

error_out:
    SetPageError(page);
out:
    pageaddr = kmap_atomic(page);
    memset(pageaddr, 0, PAGE_CACHE_SIZE);
    kunmap_atomic(pageaddr);
    flush_dcache_page(page);
    if (!PageError(page))
        SetPageUptodate(page);
    unlock_page(page);

    return 0;
}


const struct address_space_operations squashfs_aops = {
    .readpage = squashfs_readpage
};