itree.c

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/*
 *  linux/fs/sysv/itree.c
 *
 *  Handling of indirect blocks' trees.
 *  AV, Sep--Dec 2000
 */

#include <linux/buffer_head.h>
#include <linux/mount.h>
#include <linux/string.h>
#include "sysv.h"

enum {DIRECT = 10, DEPTH = 4};  /* Have triple indirect */

static inline void dirty_indirect(struct buffer_head *bh, struct inode *inode)
{
    mark_buffer_dirty_inode(bh, inode);
    if (IS_SYNC(inode))
        sync_dirty_buffer(bh);
}

static int block_to_path(struct inode *inode, long block, int offsets[DEPTH])
{
    struct super_block *sb = inode->i_sb;
    struct sysv_sb_info *sbi = SYSV_SB(sb);
    int ptrs_bits = sbi->s_ind_per_block_bits;
    unsigned long   indirect_blocks = sbi->s_ind_per_block,
            double_blocks = sbi->s_ind_per_block_2;
    int n = 0;

    if (block < 0) {
        printk("sysv_block_map: block < 0\n");
    } else if (block < DIRECT) {
        offsets[n++] = block;
    } else if ( (block -= DIRECT) < indirect_blocks) {
        offsets[n++] = DIRECT;
        offsets[n++] = block;
    } else if ((block -= indirect_blocks) < double_blocks) {
        offsets[n++] = DIRECT+1;
        offsets[n++] = block >> ptrs_bits;
        offsets[n++] = block & (indirect_blocks - 1);
    } else if (((block -= double_blocks) >> (ptrs_bits * 2)) < indirect_blocks) {
        offsets[n++] = DIRECT+2;
        offsets[n++] = block >> (ptrs_bits * 2);
        offsets[n++] = (block >> ptrs_bits) & (indirect_blocks - 1);
        offsets[n++] = block & (indirect_blocks - 1);
    } else {
        /* nothing */;
    }
    return n;
}

static inline int block_to_cpu(struct sysv_sb_info *sbi, sysv_zone_t nr)
{
    return sbi->s_block_base + fs32_to_cpu(sbi, nr);
}

typedef struct {
    sysv_zone_t     *p;
    sysv_zone_t     key;
    struct buffer_head *bh;
} Indirect;

static DEFINE_RWLOCK(pointers_lock);

static inline void add_chain(Indirect *p, struct buffer_head *bh, sysv_zone_t *v)
{
    p->key = *(p->p = v);
    p->bh = bh;
}

static inline int verify_chain(Indirect *from, Indirect *to)
{
    while (from <= to && from->key == *from->p)
        from++;
    return (from > to);
}

static inline sysv_zone_t *block_end(struct buffer_head *bh)
{
    return (sysv_zone_t*)((char*)bh->b_data + bh->b_size);
}

/*
 * Requires read_lock(&pointers_lock) or write_lock(&pointers_lock)
 */
static Indirect *get_branch(struct inode *inode,
                int depth,
                int offsets[],
                Indirect chain[],
                int *err)
{
    struct super_block *sb = inode->i_sb;
    Indirect *p = chain;
    struct buffer_head *bh;

    *err = 0;
    add_chain(chain, NULL, SYSV_I(inode)->i_data + *offsets);
    if (!p->key)
        goto no_block;
    while (--depth) {
        int block = block_to_cpu(SYSV_SB(sb), p->key);
        bh = sb_bread(sb, block);
        if (!bh)
            goto failure;
        if (!verify_chain(chain, p))
            goto changed;
        add_chain(++p, bh, (sysv_zone_t*)bh->b_data + *++offsets);
        if (!p->key)
            goto no_block;
    }
    return NULL;

changed:
    brelse(bh);
    *err = -EAGAIN;
    goto no_block;
failure:
    *err = -EIO;
no_block:
    return p;
}

static int alloc_branch(struct inode *inode,
            int num,
            int *offsets,
            Indirect *branch)
{
    int blocksize = inode->i_sb->s_blocksize;
    int n = 0;
    int i;

    branch[0].key = sysv_new_block(inode->i_sb);
    if (branch[0].key) for (n = 1; n < num; n++) {
        struct buffer_head *bh;
        int parent;
        /* Allocate the next block */
        branch[n].key = sysv_new_block(inode->i_sb);
        if (!branch[n].key)
            break;
        /*
         * Get buffer_head for parent block, zero it out and set 
         * the pointer to new one, then send parent to disk.
         */
        parent = block_to_cpu(SYSV_SB(inode->i_sb), branch[n-1].key);
        bh = sb_getblk(inode->i_sb, parent);
        lock_buffer(bh);
        memset(bh->b_data, 0, blocksize);
        branch[n].bh = bh;
        branch[n].p = (sysv_zone_t*) bh->b_data + offsets[n];
        *branch[n].p = branch[n].key;
        set_buffer_uptodate(bh);
        unlock_buffer(bh);
        dirty_indirect(bh, inode);
    }
    if (n == num)
        return 0;

    /* Allocation failed, free what we already allocated */
    for (i = 1; i < n; i++)
        bforget(branch[i].bh);
    for (i = 0; i < n; i++)
        sysv_free_block(inode->i_sb, branch[i].key);
    return -ENOSPC;
}

static inline int splice_branch(struct inode *inode,
                Indirect chain[],
                Indirect *where,
                int num)
{
    int i;

    /* Verify that place we are splicing to is still there and vacant */
    write_lock(&pointers_lock);
    if (!verify_chain(chain, where-1) || *where->p)
        goto changed;
    *where->p = where->key;
    write_unlock(&pointers_lock);

    inode->i_ctime = CURRENT_TIME_SEC;

    /* had we spliced it onto indirect block? */
    if (where->bh)
        dirty_indirect(where->bh, inode);

    if (IS_SYNC(inode))
        sysv_sync_inode(inode);
    else
        mark_inode_dirty(inode);
    return 0;

changed:
    write_unlock(&pointers_lock);
    for (i = 1; i < num; i++)
        bforget(where[i].bh);
    for (i = 0; i < num; i++)
        sysv_free_block(inode->i_sb, where[i].key);
    return -EAGAIN;
}

static int get_block(struct inode *inode, sector_t iblock, struct buffer_head *bh_result, int create)
{
    int err = -EIO;
    int offsets[DEPTH];
    Indirect chain[DEPTH];
    struct super_block *sb = inode->i_sb;
    Indirect *partial;
    int left;
    int depth = block_to_path(inode, iblock, offsets);

    if (depth == 0)
        goto out;

reread:
    read_lock(&pointers_lock);
    partial = get_branch(inode, depth, offsets, chain, &err);
    read_unlock(&pointers_lock);

    /* Simplest case - block found, no allocation needed */
    if (!partial) {
got_it:
        map_bh(bh_result, sb, block_to_cpu(SYSV_SB(sb),
                    chain[depth-1].key));
        /* Clean up and exit */
        partial = chain+depth-1; /* the whole chain */
        goto cleanup;
    }

    /* Next simple case - plain lookup or failed read of indirect block */
    if (!create || err == -EIO) {
cleanup:
        while (partial > chain) {
            brelse(partial->bh);
            partial--;
        }
out:
        return err;
    }

    /*
     * Indirect block might be removed by truncate while we were
     * reading it. Handling of that case (forget what we've got and
     * reread) is taken out of the main path.
     */
    if (err == -EAGAIN)
        goto changed;

    left = (chain + depth) - partial;
    err = alloc_branch(inode, left, offsets+(partial-chain), partial);
    if (err)
        goto cleanup;

    if (splice_branch(inode, chain, partial, left) < 0)
        goto changed;

    set_buffer_new(bh_result);
    goto got_it;

changed:
    while (partial > chain) {
        brelse(partial->bh);
        partial--;
    }
    goto reread;
}

static inline int all_zeroes(sysv_zone_t *p, sysv_zone_t *q)
{
    while (p < q)
        if (*p++)
            return 0;
    return 1;
}

static Indirect *find_shared(struct inode *inode,
                int depth,
                int offsets[],
                Indirect chain[],
                sysv_zone_t *top)
{
    Indirect *partial, *p;
    int k, err;

    *top = 0;
    for (k = depth; k > 1 && !offsets[k-1]; k--)
        ;

    write_lock(&pointers_lock);
    partial = get_branch(inode, k, offsets, chain, &err);
    if (!partial)
        partial = chain + k-1;
    /*
     * If the branch acquired continuation since we've looked at it -
     * fine, it should all survive and (new) top doesn't belong to us.
     */
    if (!partial->key && *partial->p) {
        write_unlock(&pointers_lock);
        goto no_top;
    }
    for (p=partial; p>chain && all_zeroes((sysv_zone_t*)p->bh->b_data,p->p); p--)
        ;
    /*
     * OK, we've found the last block that must survive. The rest of our
     * branch should be detached before unlocking. However, if that rest
     * of branch is all ours and does not grow immediately from the inode
     * it's easier to cheat and just decrement partial->p.
     */
    if (p == chain + k - 1 && p > chain) {
        p->p--;
    } else {
        *top = *p->p;
        *p->p = 0;
    }
    write_unlock(&pointers_lock);

    while (partial > p) {
        brelse(partial->bh);
        partial--;
    }
no_top:
    return partial;
}

static inline void free_data(struct inode *inode, sysv_zone_t *p, sysv_zone_t *q)
{
    for ( ; p < q ; p++) {
        sysv_zone_t nr = *p;
        if (nr) {
            *p = 0;
            sysv_free_block(inode->i_sb, nr);
            mark_inode_dirty(inode);
        }
    }
}

static void free_branches(struct inode *inode, sysv_zone_t *p, sysv_zone_t *q, int depth)
{
    struct buffer_head * bh;
    struct super_block *sb = inode->i_sb;

    if (depth--) {
        for ( ; p < q ; p++) {
            int block;
            sysv_zone_t nr = *p;
            if (!nr)
                continue;
            *p = 0;
            block = block_to_cpu(SYSV_SB(sb), nr);
            bh = sb_bread(sb, block);
            if (!bh)
                continue;
            free_branches(inode, (sysv_zone_t*)bh->b_data,
                    block_end(bh), depth);
            bforget(bh);
            sysv_free_block(sb, nr);
            mark_inode_dirty(inode);
        }
    } else
        free_data(inode, p, q);
}

void sysv_truncate (struct inode * inode)
{
    sysv_zone_t *i_data = SYSV_I(inode)->i_data;
    int offsets[DEPTH];
    Indirect chain[DEPTH];
    Indirect *partial;
    sysv_zone_t nr = 0;
    int n;
    long iblock;
    unsigned blocksize;

    if (!(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
        S_ISLNK(inode->i_mode)))
        return;

    blocksize = inode->i_sb->s_blocksize;
    iblock = (inode->i_size + blocksize-1)
                    >> inode->i_sb->s_blocksize_bits;

    block_truncate_page(inode->i_mapping, inode->i_size, get_block);

    n = block_to_path(inode, iblock, offsets);
    if (n == 0)
        return;

    if (n == 1) {
        free_data(inode, i_data+offsets[0], i_data + DIRECT);
        goto do_indirects;
    }

    partial = find_shared(inode, n, offsets, chain, &nr);
    /* Kill the top of shared branch (already detached) */
    if (nr) {
        if (partial == chain)
            mark_inode_dirty(inode);
        else
            dirty_indirect(partial->bh, inode);
        free_branches(inode, &nr, &nr+1, (chain+n-1) - partial);
    }
    /* Clear the ends of indirect blocks on the shared branch */
    while (partial > chain) {
        free_branches(inode, partial->p + 1, block_end(partial->bh),
                (chain+n-1) - partial);
        dirty_indirect(partial->bh, inode);
        brelse (partial->bh);
        partial--;
    }
do_indirects:
    /* Kill the remaining (whole) subtrees (== subtrees deeper than...) */
    while (n < DEPTH) {
        nr = i_data[DIRECT + n - 1];
        if (nr) {
            i_data[DIRECT + n - 1] = 0;
            mark_inode_dirty(inode);
            free_branches(inode, &nr, &nr+1, n);
        }
        n++;
    }
    inode->i_mtime = inode->i_ctime = CURRENT_TIME_SEC;
    if (IS_SYNC(inode))
        sysv_sync_inode (inode);
    else
        mark_inode_dirty(inode);
}

static unsigned sysv_nblocks(struct super_block *s, loff_t size)
{
    struct sysv_sb_info *sbi = SYSV_SB(s);
    int ptrs_bits = sbi->s_ind_per_block_bits;
    unsigned blocks, res, direct = DIRECT, i = DEPTH;
    blocks = (size + s->s_blocksize - 1) >> s->s_blocksize_bits;
    res = blocks;
    while (--i && blocks > direct) {
        blocks = ((blocks - direct - 1) >> ptrs_bits) + 1;
        res += blocks;
        direct = 1;
    }
    return blocks;
}

int sysv_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
{
    struct super_block *s = dentry->d_sb;
    generic_fillattr(dentry->d_inode, stat);
    stat->blocks = (s->s_blocksize / 512) * sysv_nblocks(s, stat->size);
    stat->blksize = s->s_blocksize;
    return 0;
}

static int sysv_writepage(struct page *page, struct writeback_control *wbc)
{
    return block_write_full_page(page,get_block,wbc);
}

static int sysv_readpage(struct file *file, struct page *page)
{
    return block_read_full_page(page,get_block);
}

int sysv_prepare_chunk(struct page *page, loff_t pos, unsigned len)
{
    return __block_write_begin(page, pos, len, get_block);
}

static int sysv_write_begin(struct file *file, struct address_space *mapping,
            loff_t pos, unsigned len, unsigned flags,
            struct page **pagep, void **fsdata)
{
    int ret;

    ret = block_write_begin(mapping, pos, len, flags, pagep, get_block);
    if (unlikely(ret)) {
        loff_t isize = mapping->host->i_size;
        if (pos + len > isize)
            vmtruncate(mapping->host, isize);
    }

    return ret;
}

static sector_t sysv_bmap(struct address_space *mapping, sector_t block)
{
    return generic_block_bmap(mapping,block,get_block);
}

const struct address_space_operations sysv_aops = {
    .readpage = sysv_readpage,
    .writepage = sysv_writepage,
    .write_begin = sysv_write_begin,
    .write_end = generic_write_end,
    .bmap = sysv_bmap
};