export.c

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/*
 * fs/isofs/export.c
 *
 *  (C) 2004  Paul Serice - The new inode scheme requires switching
 *                          from iget() to iget5_locked() which means
 *                          the NFS export operations have to be hand
 *                          coded because the default routines rely on
 *                          iget().
 *
 * The following files are helpful:
 *
 *     Documentation/filesystems/nfs/Exporting
 *     fs/exportfs/expfs.c.
 */

#include "isofs.h"

static struct dentry *
isofs_export_iget(struct super_block *sb,
          unsigned long block,
          unsigned long offset,
          __u32 generation)
{
    struct inode *inode;

    if (block == 0)
        return ERR_PTR(-ESTALE);
    inode = isofs_iget(sb, block, offset);
    if (IS_ERR(inode))
        return ERR_CAST(inode);
    if (generation && inode->i_generation != generation) {
        iput(inode);
        return ERR_PTR(-ESTALE);
    }
    return d_obtain_alias(inode);
}

/* This function is surprisingly simple.  The trick is understanding
 * that "child" is always a directory. So, to find its parent, you
 * simply need to find its ".." entry, normalize its block and offset,
 * and return the underlying inode.  See the comments for
 * isofs_normalize_block_and_offset(). */
static struct dentry *isofs_export_get_parent(struct dentry *child)
{
    unsigned long parent_block = 0;
    unsigned long parent_offset = 0;
    struct inode *child_inode = child->d_inode;
    struct iso_inode_info *e_child_inode = ISOFS_I(child_inode);
    struct iso_directory_record *de = NULL;
    struct buffer_head * bh = NULL;
    struct dentry *rv = NULL;

    /* "child" must always be a directory. */
    if (!S_ISDIR(child_inode->i_mode)) {
        printk(KERN_ERR "isofs: isofs_export_get_parent(): "
               "child is not a directory!\n");
        rv = ERR_PTR(-EACCES);
        goto out;
    }

    /* It is an invariant that the directory offset is zero.  If
     * it is not zero, it means the directory failed to be
     * normalized for some reason. */
    if (e_child_inode->i_iget5_offset != 0) {
        printk(KERN_ERR "isofs: isofs_export_get_parent(): "
               "child directory not normalized!\n");
        rv = ERR_PTR(-EACCES);
        goto out;
    }

    /* The child inode has been normalized such that its
     * i_iget5_block value points to the "." entry.  Fortunately,
     * the ".." entry is located in the same block. */
    parent_block = e_child_inode->i_iget5_block;

    /* Get the block in question. */
    bh = sb_bread(child_inode->i_sb, parent_block);
    if (bh == NULL) {
        rv = ERR_PTR(-EACCES);
        goto out;
    }

    /* This is the "." entry. */
    de = (struct iso_directory_record*)bh->b_data;

    /* The ".." entry is always the second entry. */
    parent_offset = (unsigned long)isonum_711(de->length);
    de = (struct iso_directory_record*)(bh->b_data + parent_offset);

    /* Verify it is in fact the ".." entry. */
    if ((isonum_711(de->name_len) != 1) || (de->name[0] != 1)) {
        printk(KERN_ERR "isofs: Unable to find the \"..\" "
               "directory for NFS.\n");
        rv = ERR_PTR(-EACCES);
        goto out;
    }

    /* Normalize */
    isofs_normalize_block_and_offset(de, &parent_block, &parent_offset);

    rv = d_obtain_alias(isofs_iget(child_inode->i_sb, parent_block,
                     parent_offset));
 out:
    if (bh)
        brelse(bh);
    return rv;
}

static int
isofs_export_encode_fh(struct inode *inode,
               __u32 *fh32,
               int *max_len,
               struct inode *parent)
{
    struct iso_inode_info * ei = ISOFS_I(inode);
    int len = *max_len;
    int type = 1;
    __u16 *fh16 = (__u16*)fh32;

    /*
     * WARNING: max_len is 5 for NFSv2.  Because of this
     * limitation, we use the lower 16 bits of fh32[1] to hold the
     * offset of the inode and the upper 16 bits of fh32[1] to
     * hold the offset of the parent.
     */
    if (parent && (len < 5)) {
        *max_len = 5;
        return 255;
    } else if (len < 3) {
        *max_len = 3;
        return 255;
    }

    len = 3;
    fh32[0] = ei->i_iget5_block;
    fh16[2] = (__u16)ei->i_iget5_offset;  /* fh16 [sic] */
    fh16[3] = 0;  /* avoid leaking uninitialized data */
    fh32[2] = inode->i_generation;
    if (parent) {
        struct iso_inode_info *eparent;
        eparent = ISOFS_I(parent);
        fh32[3] = eparent->i_iget5_block;
        fh16[3] = (__u16)eparent->i_iget5_offset;  /* fh16 [sic] */
        fh32[4] = parent->i_generation;
        len = 5;
        type = 2;
    }
    *max_len = len;
    return type;
}

struct isofs_fid {
    u32 block;
    u16 offset;
    u16 parent_offset;
    u32 generation;
    u32 parent_block;
    u32 parent_generation;
};

static struct dentry *isofs_fh_to_dentry(struct super_block *sb,
    struct fid *fid, int fh_len, int fh_type)
{
    struct isofs_fid *ifid = (struct isofs_fid *)fid;

    if (fh_len < 3 || fh_type > 2)
        return NULL;

    return isofs_export_iget(sb, ifid->block, ifid->offset,
            ifid->generation);
}

static struct dentry *isofs_fh_to_parent(struct super_block *sb,
        struct fid *fid, int fh_len, int fh_type)
{
    struct isofs_fid *ifid = (struct isofs_fid *)fid;

    if (fh_len < 2 || fh_type != 2)
        return NULL;

    return isofs_export_iget(sb,
            fh_len > 2 ? ifid->parent_block : 0,
            ifid->parent_offset,
            fh_len > 4 ? ifid->parent_generation : 0);
}

const struct export_operations isofs_export_ops = {
    .encode_fh  = isofs_export_encode_fh,
    .fh_to_dentry   = isofs_fh_to_dentry,
    .fh_to_parent   = isofs_fh_to_parent,
    .get_parent     = isofs_export_get_parent,
};