linux/fs/isofs/export.c
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   1/*
   2 * fs/isofs/export.c
   3 *
   4 *  (C) 2004  Paul Serice - The new inode scheme requires switching
   5 *                          from iget() to iget5_locked() which means
   6 *                          the NFS export operations have to be hand
   7 *                          coded because the default routines rely on
   8 *                          iget().
   9 *
  10 * The following files are helpful:
  11 *
  12 *     Documentation/filesystems/nfs/Exporting
  13 *     fs/exportfs/expfs.c.
  14 */
  15
  16#include "isofs.h"
  17
  18static struct dentry *
  19isofs_export_iget(struct super_block *sb,
  20                  unsigned long block,
  21                  unsigned long offset,
  22                  __u32 generation)
  23{
  24        struct inode *inode;
  25
  26        if (block == 0)
  27                return ERR_PTR(-ESTALE);
  28        inode = isofs_iget(sb, block, offset);
  29        if (IS_ERR(inode))
  30                return ERR_CAST(inode);
  31        if (generation && inode->i_generation != generation) {
  32                iput(inode);
  33                return ERR_PTR(-ESTALE);
  34        }
  35        return d_obtain_alias(inode);
  36}
  37
  38/* This function is surprisingly simple.  The trick is understanding
  39 * that "child" is always a directory. So, to find its parent, you
  40 * simply need to find its ".." entry, normalize its block and offset,
  41 * and return the underlying inode.  See the comments for
  42 * isofs_normalize_block_and_offset(). */
  43static struct dentry *isofs_export_get_parent(struct dentry *child)
  44{
  45        unsigned long parent_block = 0;
  46        unsigned long parent_offset = 0;
  47        struct inode *child_inode = child->d_inode;
  48        struct iso_inode_info *e_child_inode = ISOFS_I(child_inode);
  49        struct iso_directory_record *de = NULL;
  50        struct buffer_head * bh = NULL;
  51        struct dentry *rv = NULL;
  52
  53        /* "child" must always be a directory. */
  54        if (!S_ISDIR(child_inode->i_mode)) {
  55                printk(KERN_ERR "isofs: isofs_export_get_parent(): "
  56                       "child is not a directory!\n");
  57                rv = ERR_PTR(-EACCES);
  58                goto out;
  59        }
  60
  61        /* It is an invariant that the directory offset is zero.  If
  62         * it is not zero, it means the directory failed to be
  63         * normalized for some reason. */
  64        if (e_child_inode->i_iget5_offset != 0) {
  65                printk(KERN_ERR "isofs: isofs_export_get_parent(): "
  66                       "child directory not normalized!\n");
  67                rv = ERR_PTR(-EACCES);
  68                goto out;
  69        }
  70
  71        /* The child inode has been normalized such that its
  72         * i_iget5_block value points to the "." entry.  Fortunately,
  73         * the ".." entry is located in the same block. */
  74        parent_block = e_child_inode->i_iget5_block;
  75
  76        /* Get the block in question. */
  77        bh = sb_bread(child_inode->i_sb, parent_block);
  78        if (bh == NULL) {
  79                rv = ERR_PTR(-EACCES);
  80                goto out;
  81        }
  82
  83        /* This is the "." entry. */
  84        de = (struct iso_directory_record*)bh->b_data;
  85
  86        /* The ".." entry is always the second entry. */
  87        parent_offset = (unsigned long)isonum_711(de->length);
  88        de = (struct iso_directory_record*)(bh->b_data + parent_offset);
  89
  90        /* Verify it is in fact the ".." entry. */
  91        if ((isonum_711(de->name_len) != 1) || (de->name[0] != 1)) {
  92                printk(KERN_ERR "isofs: Unable to find the \"..\" "
  93                       "directory for NFS.\n");
  94                rv = ERR_PTR(-EACCES);
  95                goto out;
  96        }
  97
  98        /* Normalize */
  99        isofs_normalize_block_and_offset(de, &parent_block, &parent_offset);
 100
 101        rv = d_obtain_alias(isofs_iget(child_inode->i_sb, parent_block,
 102                                     parent_offset));
 103 out:
 104        if (bh)
 105                brelse(bh);
 106        return rv;
 107}
 108
 109static int
 110isofs_export_encode_fh(struct inode *inode,
 111                       __u32 *fh32,
 112                       int *max_len,
 113                       struct inode *parent)
 114{
 115        struct iso_inode_info * ei = ISOFS_I(inode);
 116        int len = *max_len;
 117        int type = 1;
 118        __u16 *fh16 = (__u16*)fh32;
 119
 120        /*
 121         * WARNING: max_len is 5 for NFSv2.  Because of this
 122         * limitation, we use the lower 16 bits of fh32[1] to hold the
 123         * offset of the inode and the upper 16 bits of fh32[1] to
 124         * hold the offset of the parent.
 125         */
 126        if (parent && (len < 5)) {
 127                *max_len = 5;
 128                return 255;
 129        } else if (len < 3) {
 130                *max_len = 3;
 131                return 255;
 132        }
 133
 134        len = 3;
 135        fh32[0] = ei->i_iget5_block;
 136        fh16[2] = (__u16)ei->i_iget5_offset;  /* fh16 [sic] */
 137        fh16[3] = 0;  /* avoid leaking uninitialized data */
 138        fh32[2] = inode->i_generation;
 139        if (parent) {
 140                struct iso_inode_info *eparent;
 141                eparent = ISOFS_I(parent);
 142                fh32[3] = eparent->i_iget5_block;
 143                fh16[3] = (__u16)eparent->i_iget5_offset;  /* fh16 [sic] */
 144                fh32[4] = parent->i_generation;
 145                len = 5;
 146                type = 2;
 147        }
 148        *max_len = len;
 149        return type;
 150}
 151
 152struct isofs_fid {
 153        u32 block;
 154        u16 offset;
 155        u16 parent_offset;
 156        u32 generation;
 157        u32 parent_block;
 158        u32 parent_generation;
 159};
 160
 161static struct dentry *isofs_fh_to_dentry(struct super_block *sb,
 162        struct fid *fid, int fh_len, int fh_type)
 163{
 164        struct isofs_fid *ifid = (struct isofs_fid *)fid;
 165
 166        if (fh_len < 3 || fh_type > 2)
 167                return NULL;
 168
 169        return isofs_export_iget(sb, ifid->block, ifid->offset,
 170                        ifid->generation);
 171}
 172
 173static struct dentry *isofs_fh_to_parent(struct super_block *sb,
 174                struct fid *fid, int fh_len, int fh_type)
 175{
 176        struct isofs_fid *ifid = (struct isofs_fid *)fid;
 177
 178        if (fh_len < 2 || fh_type != 2)
 179                return NULL;
 180
 181        return isofs_export_iget(sb,
 182                        fh_len > 2 ? ifid->parent_block : 0,
 183                        ifid->parent_offset,
 184                        fh_len > 4 ? ifid->parent_generation : 0);
 185}
 186
 187const struct export_operations isofs_export_ops = {
 188        .encode_fh      = isofs_export_encode_fh,
 189        .fh_to_dentry   = isofs_fh_to_dentry,
 190        .fh_to_parent   = isofs_fh_to_parent,
 191        .get_parent     = isofs_export_get_parent,
 192};
 193
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