include/linux/exportfs.h

   1 #ifndef LINUX_EXPORTFS_H
   2 #define LINUX_EXPORTFS_H 1
   3
   4 #include <linux/types.h>
   5
   6 struct dentry;
   7 struct super_block;
   8 struct vfsmount;
   9
  10 /*
  11  * The fileid_type identifies how the file within the filesystem is encoded.
  12  * In theory this is freely set and parsed by the filesystem, but we try to
  13  * stick to conventions so we can share some generic code and don't confuse
  14  * sniffers like ethereal/wireshark.
  15  *
  16  * The filesystem must not use the value '0' or '0xff'.
  17  */
  18 enum fid_type {
  19         /*
  20          * The root, or export point, of the filesystem.
  21          * (Never actually passed down to the filesystem.
  22          */
  23         FILEID_ROOT = 0,
  24
  25         /*
  26          * 32bit inode number, 32 bit generation number.
  27          */
  28         FILEID_INO32_GEN = 1,
  29
  30         /*
  31          * 32bit inode number, 32 bit generation number,
  32          * 32 bit parent directory inode number.
  33          */
  34         FILEID_INO32_GEN_PARENT = 2,
  35 };
  36
  37 struct fid {
  38         union {
  39                 struct {
  40                         u32 ino;
  41                         u32 gen;
  42                         u32 parent_ino;
  43                         u32 parent_gen;
  44                 } i32;
  45                 __u32 raw[6];
  46         };
  47 };
  48
  49 /**
  50  * struct export_operations - for nfsd to communicate with file systems
  51  * @decode_fh:      decode a file handle fragment and return a &struct dentry
  52  * @encode_fh:      encode a file handle fragment from a dentry
  53  * @get_name:       find the name for a given inode in a given directory
  54  * @get_parent:     find the parent of a given directory
  55  * @get_dentry:     find a dentry for the inode given a file handle sub-fragment
  56  * @find_exported_dentry:
  57  *      set by the exporting module to a standard helper function.
  58  *
  59  * Description:
  60  *    The export_operations structure provides a means for nfsd to communicate
  61  *    with a particular exported file system  - particularly enabling nfsd and
  62  *    the filesystem to co-operate when dealing with file handles.
  63  *
  64  *    export_operations contains two basic operation for dealing with file
  65  *    handles, decode_fh() and encode_fh(), and allows for some other
  66  *    operations to be defined which standard helper routines use to get
  67  *    specific information from the filesystem.
  68  *
  69  *    nfsd encodes information use to determine which filesystem a filehandle
  70  *    applies to in the initial part of the file handle.  The remainder, termed
  71  *    a file handle fragment, is controlled completely by the filesystem.  The
  72  *    standard helper routines assume that this fragment will contain one or
  73  *    two sub-fragments, one which identifies the file, and one which may be
  74  *    used to identify the (a) directory containing the file.
  75  *
  76  *    In some situations, nfsd needs to get a dentry which is connected into a
  77  *    specific part of the file tree.  To allow for this, it passes the
  78  *    function acceptable() together with a @context which can be used to see
  79  *    if the dentry is acceptable.  As there can be multiple dentrys for a
  80  *    given file, the filesystem should check each one for acceptability before
  81  *    looking for the next.  As soon as an acceptable one is found, it should
  82  *    be returned.
  83  *
  84  * decode_fh:
  85  *    @decode_fh is given a &struct super_block (@sb), a file handle fragment
  86  *    (@fh, @fh_len) and an acceptability testing function (@acceptable,
  87  *    @context).  It should return a &struct dentry which refers to the same
  88  *    file that the file handle fragment refers to,  and which passes the
  89  *    acceptability test.  If it cannot, it should return a %NULL pointer if
  90  *    the file was found but no acceptable &dentries were available, or a
  91  *    %ERR_PTR error code indicating why it couldn't be found (e.g. %ENOENT or
  92  *    %ENOMEM).
  93  *
  94  * encode_fh:
  95  *    @encode_fh should store in the file handle fragment @fh (using at most
  96  *    @max_len bytes) information that can be used by @decode_fh to recover the
  97  *    file refered to by the &struct dentry @de.  If the @connectable flag is
  98  *    set, the encode_fh() should store sufficient information so that a good
  99  *    attempt can be made to find not only the file but also it's place in the
 100  *    filesystem.   This typically means storing a reference to de->d_parent in
 101  *    the filehandle fragment.  encode_fh() should return the number of bytes
 102  *    stored or a negative error code such as %-ENOSPC
 103  *
 104  * get_name:
 105  *    @get_name should find a name for the given @child in the given @parent
 106  *    directory.  The name should be stored in the @name (with the
 107  *    understanding that it is already pointing to a a %NAME_MAX+1 sized
 108  *    buffer.   get_name() should return %0 on success, a negative error code
 109  *    or error.  @get_name will be called without @parent->i_mutex held.
 110  *
 111  * get_parent:
 112  *    @get_parent should find the parent directory for the given @child which
 113  *    is also a directory.  In the event that it cannot be found, or storage
 114  *    space cannot be allocated, a %ERR_PTR should be returned.
 115  *
 116  * get_dentry:
 117  *    Given a &super_block (@sb) and a pointer to a file-system specific inode
 118  *    identifier, possibly an inode number, (@inump) get_dentry() should find
 119  *    the identified inode and return a dentry for that inode.  Any suitable
 120  *    dentry can be returned including, if necessary, a new dentry created with
 121  *    d_alloc_root.  The caller can then find any other extant dentrys by
 122  *    following the d_alias links.  If a new dentry was created using
 123  *    d_alloc_root, DCACHE_NFSD_DISCONNECTED should be set, and the dentry
 124  *    should be d_rehash()ed.
 125  *
 126  *    If the inode cannot be found, either a %NULL pointer or an %ERR_PTR code
 127  *    can be returned.  The @inump will be whatever was passed to
 128  *    nfsd_find_fh_dentry() in either the @obj or @parent parameters.
 129  *
 130  * Locking rules:
 131  *    get_parent is called with child->d_inode->i_mutex down
 132  *    get_name is not (which is possibly inconsistent)
 133  */
 134
 135 struct export_operations {
 136         struct dentry *(*decode_fh)(struct super_block *sb, __u32 *fh,
 137                         int fh_len, int fh_type,
 138                         int (*acceptable)(void *context, struct dentry *de),
 139                         void *context);
 140         int (*encode_fh)(struct dentry *de, __u32 *fh, int *max_len,
 141                         int connectable);
 142         int (*get_name)(struct dentry *parent, char *name,
 143                         struct dentry *child);
 144         struct dentry * (*get_parent)(struct dentry *child);
 145         struct dentry * (*get_dentry)(struct super_block *sb, void *inump);
 146
 147         /* This is set by the exporting module to a standard helper */
 148         struct dentry * (*find_exported_dentry)(
 149                         struct super_block *sb, void *obj, void *parent,
 150                         int (*acceptable)(void *context, struct dentry *de),
 151                         void *context);
 152 };
 153
 154 extern struct dentry *find_exported_dentry(struct super_block *sb, void *obj,
 155         void *parent, int (*acceptable)(void *context, struct dentry *de),
 156         void *context);
 157
 158 extern int exportfs_encode_fh(struct dentry *dentry, struct fid *fid,
 159         int *max_len, int connectable);
 160 extern struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
 161         int fh_len, int fileid_type, int (*acceptable)(void *, struct dentry *),
 162         void *context);
 163
 164 #endif /* LINUX_EXPORTFS_H */