itree_common.c

Go to the documentation of this file.

/* Generic part */

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

static DEFINE_RWLOCK(pointers_lock);

static inline void add_chain(Indirect *p, struct buffer_head *bh, block_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 block_t *block_end(struct buffer_head *bh)
{
    return (block_t *)((char*)bh->b_data + bh->b_size);
}

static inline Indirect *get_branch(struct inode *inode,
                    int depth,
                    int *offsets,
                    Indirect chain[DEPTH],
                    int *err)
{
    struct super_block *sb = inode->i_sb;
    Indirect *p = chain;
    struct buffer_head *bh;

    *err = 0;
    /* i_data is not going away, no lock needed */
    add_chain (chain, NULL, i_data(inode) + *offsets);
    if (!p->key)
        goto no_block;
    while (--depth) {
        bh = sb_bread(sb, block_to_cpu(p->key));
        if (!bh)
            goto failure;
        read_lock(&pointers_lock);
        if (!verify_chain(chain, p))
            goto changed;
        add_chain(++p, bh, (block_t *)bh->b_data + *++offsets);
        read_unlock(&pointers_lock);
        if (!p->key)
            goto no_block;
    }
    return NULL;

changed:
    read_unlock(&pointers_lock);
    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 n = 0;
    int i;
    int parent = minix_new_block(inode);

    branch[0].key = cpu_to_block(parent);
    if (parent) for (n = 1; n < num; n++) {
        struct buffer_head *bh;
        /* Allocate the next block */
        int nr = minix_new_block(inode);
        if (!nr)
            break;
        branch[n].key = cpu_to_block(nr);
        bh = sb_getblk(inode->i_sb, parent);
        lock_buffer(bh);
        memset(bh->b_data, 0, bh->b_size);
        branch[n].bh = bh;
        branch[n].p = (block_t*) bh->b_data + offsets[n];
        *branch[n].p = branch[n].key;
        set_buffer_uptodate(bh);
        unlock_buffer(bh);
        mark_buffer_dirty_inode(bh, inode);
        parent = nr;
    }
    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++)
        minix_free_block(inode, block_to_cpu(branch[i].key));
    return -ENOSPC;
}

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

    write_lock(&pointers_lock);

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

    *where->p = where->key;

    write_unlock(&pointers_lock);

    /* We are done with atomic stuff, now do the rest of housekeeping */

    inode->i_ctime = CURRENT_TIME_SEC;

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

    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++)
        minix_free_block(inode, block_to_cpu(where[i].key));
    return -EAGAIN;
}

static inline int get_block(struct inode * inode, sector_t block,
            struct buffer_head *bh, int create)
{
    int err = -EIO;
    int offsets[DEPTH];
    Indirect chain[DEPTH];
    Indirect *partial;
    int left;
    int depth = block_to_path(inode, block, offsets);

    if (depth == 0)
        goto out;

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

    /* Simplest case - block found, no allocation needed */
    if (!partial) {
got_it:
        map_bh(bh, inode->i_sb, block_to_cpu(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);
    goto got_it;

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

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

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

    *top = 0;
    for (k = depth; k > 1 && !offsets[k-1]; k--)
        ;
    partial = get_branch(inode, k, offsets, chain, &err);

    write_lock(&pointers_lock);
    if (!partial)
        partial = chain + k-1;
    if (!partial->key && *partial->p) {
        write_unlock(&pointers_lock);
        goto no_top;
    }
    for (p=partial;p>chain && all_zeroes((block_t*)p->bh->b_data,p->p);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, block_t *p, block_t *q)
{
    unsigned long nr;

    for ( ; p < q ; p++) {
        nr = block_to_cpu(*p);
        if (nr) {
            *p = 0;
            minix_free_block(inode, nr);
        }
    }
}

static void free_branches(struct inode *inode, block_t *p, block_t *q, int depth)
{
    struct buffer_head * bh;
    unsigned long nr;

    if (depth--) {
        for ( ; p < q ; p++) {
            nr = block_to_cpu(*p);
            if (!nr)
                continue;
            *p = 0;
            bh = sb_bread(inode->i_sb, nr);
            if (!bh)
                continue;
            free_branches(inode, (block_t*)bh->b_data,
                      block_end(bh), depth);
            bforget(bh);
            minix_free_block(inode, nr);
            mark_inode_dirty(inode);
        }
    } else
        free_data(inode, p, q);
}

static inline void truncate (struct inode * inode)
{
    struct super_block *sb = inode->i_sb;
    block_t *idata = i_data(inode);
    int offsets[DEPTH];
    Indirect chain[DEPTH];
    Indirect *partial;
    block_t nr = 0;
    int n;
    int first_whole;
    long iblock;

    iblock = (inode->i_size + sb->s_blocksize -1) >> sb->s_blocksize_bits;
    block_truncate_page(inode->i_mapping, inode->i_size, get_block);

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

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

    first_whole = offsets[0] + 1 - DIRECT;
    partial = find_shared(inode, n, offsets, chain, &nr);
    if (nr) {
        if (partial == chain)
            mark_inode_dirty(inode);
        else
            mark_buffer_dirty_inode(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);
        mark_buffer_dirty_inode(partial->bh, inode);
        brelse (partial->bh);
        partial--;
    }
do_indirects:
    /* Kill the remaining (whole) subtrees */
    while (first_whole < DEPTH-1) {
        nr = idata[DIRECT+first_whole];
        if (nr) {
            idata[DIRECT+first_whole] = 0;
            mark_inode_dirty(inode);
            free_branches(inode, &nr, &nr+1, first_whole+1);
        }
        first_whole++;
    }
    inode->i_mtime = inode->i_ctime = CURRENT_TIME_SEC;
    mark_inode_dirty(inode);
}

static inline unsigned nblocks(loff_t size, struct super_block *sb)
{
    int k = sb->s_blocksize_bits - 10;
    unsigned blocks, res, direct = DIRECT, i = DEPTH;
    blocks = (size + sb->s_blocksize - 1) >> (BLOCK_SIZE_BITS + k);
    res = blocks;
    while (--i && blocks > direct) {
        blocks -= direct;
        blocks += sb->s_blocksize/sizeof(block_t) - 1;
        blocks /= sb->s_blocksize/sizeof(block_t);
        res += blocks;
        direct = 1;
    }
    return res;
}