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 /**
  12  * struct export_operations - for nfsd to communicate with file systems
  13  * @decode_fh:      decode a file handle fragment and return a &struct dentry
  14  * @encode_fh:      encode a file handle fragment from a dentry
  15  * @get_name:       find the name for a given inode in a given directory
  16  * @get_parent:     find the parent of a given directory
  17  * @get_dentry:     find a dentry for the inode given a file handle sub-fragment
  18  * @find_exported_dentry:
  19  *      set by the exporting module to a standard helper function.
  20  *
  21  * Description:
  22  *    The export_operations structure provides a means for nfsd to communicate
  23  *    with a particular exported file system  - particularly enabling nfsd and
  24  *    the filesystem to co-operate when dealing with file handles.
  25  *
  26  *    export_operations contains two basic operation for dealing with file
  27  *    handles, decode_fh() and encode_fh(), and allows for some other
  28  *    operations to be defined which standard helper routines use to get
  29  *    specific information from the filesystem.
  30  *
  31  *    nfsd encodes information use to determine which filesystem a filehandle
  32  *    applies to in the initial part of the file handle.  The remainder, termed
  33  *    a file handle fragment, is controlled completely by the filesystem.  The
  34  *    standard helper routines assume that this fragment will contain one or
  35  *    two sub-fragments, one which identifies the file, and one which may be
  36  *    used to identify the (a) directory containing the file.
  37  *
  38  *    In some situations, nfsd needs to get a dentry which is connected into a
  39  *    specific part of the file tree.  To allow for this, it passes the
  40  *    function acceptable() together with a @context which can be used to see
  41  *    if the dentry is acceptable.  As there can be multiple dentrys for a
  42  *    given file, the filesystem should check each one for acceptability before
  43  *    looking for the next.  As soon as an acceptable one is found, it should
  44  *    be returned.
  45  *
  46  * decode_fh:
  47  *    @decode_fh is given a &struct super_block (@sb), a file handle fragment
  48  *    (@fh, @fh_len) and an acceptability testing function (@acceptable,
  49  *    @context).  It should return a &struct dentry which refers to the same
  50  *    file that the file handle fragment refers to,  and which passes the
  51  *    acceptability test.  If it cannot, it should return a %NULL pointer if
  52  *    the file was found but no acceptable &dentries were available, or a
  53  *    %ERR_PTR error code indicating why it couldn't be found (e.g. %ENOENT or
  54  *    %ENOMEM).
  55  *
  56  * encode_fh:
  57  *    @encode_fh should store in the file handle fragment @fh (using at most
  58  *    @max_len bytes) information that can be used by @decode_fh to recover the
  59  *    file refered to by the &struct dentry @de.  If the @connectable flag is
  60  *    set, the encode_fh() should store sufficient information so that a good
  61  *    attempt can be made to find not only the file but also it's place in the
  62  *    filesystem.   This typically means storing a reference to de->d_parent in
  63  *    the filehandle fragment.  encode_fh() should return the number of bytes
  64  *    stored or a negative error code such as %-ENOSPC
  65  *
  66  * get_name:
  67  *    @get_name should find a name for the given @child in the given @parent
  68  *    directory.  The name should be stored in the @name (with the
  69  *    understanding that it is already pointing to a a %NAME_MAX+1 sized
  70  *    buffer.   get_name() should return %0 on success, a negative error code
  71  *    or error.  @get_name will be called without @parent->i_mutex held.
  72  *
  73  * get_parent:
  74  *    @get_parent should find the parent directory for the given @child which
  75  *    is also a directory.  In the event that it cannot be found, or storage
  76  *    space cannot be allocated, a %ERR_PTR should be returned.
  77  *
  78  * get_dentry:
  79  *    Given a &super_block (@sb) and a pointer to a file-system specific inode
  80  *    identifier, possibly an inode number, (@inump) get_dentry() should find
  81  *    the identified inode and return a dentry for that inode.  Any suitable
  82  *    dentry can be returned including, if necessary, a new dentry created with
  83  *    d_alloc_root.  The caller can then find any other extant dentrys by
  84  *    following the d_alias links.  If a new dentry was created using
  85  *    d_alloc_root, DCACHE_NFSD_DISCONNECTED should be set, and the dentry
  86  *    should be d_rehash()ed.
  87  *
  88  *    If the inode cannot be found, either a %NULL pointer or an %ERR_PTR code
  89  *    can be returned.  The @inump will be whatever was passed to
  90  *    nfsd_find_fh_dentry() in either the @obj or @parent parameters.
  91  *
  92  * Locking rules:
  93  *    get_parent is called with child->d_inode->i_mutex down
  94  *    get_name is not (which is possibly inconsistent)
  95  */
  96
  97 struct export_operations {
  98         struct dentry *(*decode_fh)(struct super_block *sb, __u32 *fh,
  99                         int fh_len, int fh_type,
 100                         int (*acceptable)(void *context, struct dentry *de),
 101                         void *context);
 102         int (*encode_fh)(struct dentry *de, __u32 *fh, int *max_len,
 103                         int connectable);
 104         int (*get_name)(struct dentry *parent, char *name,
 105                         struct dentry *child);
 106         struct dentry * (*get_parent)(struct dentry *child);
 107         struct dentry * (*get_dentry)(struct super_block *sb, void *inump);
 108
 109         /* This is set by the exporting module to a standard helper */
 110         struct dentry * (*find_exported_dentry)(
 111                         struct super_block *sb, void *obj, void *parent,
 112                         int (*acceptable)(void *context, struct dentry *de),
 113                         void *context);
 114 };
 115
 116 extern struct dentry *find_exported_dentry(struct super_block *sb, void *obj,
 117         void *parent, int (*acceptable)(void *context, struct dentry *de),
 118         void *context);
 119
 120 extern int exportfs_encode_fh(struct dentry *dentry, __u32 *fh, int *max_len,
 121         int connectable);
 122 extern struct dentry *exportfs_decode_fh(struct vfsmount *mnt, __u32 *fh,
 123         int fh_len, int fileid_type, int (*acceptable)(void *, struct dentry *),
 124         void *context);
 125
 126 #endif /* LINUX_EXPORTFS_H */