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1#ifndef LINUX_EXPORTFS_H
2#define LINUX_EXPORTFS_H 1
3
4#include <linux/types.h>
5
6struct dentry;
7struct super_block;
8struct 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
97struct 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
116extern 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
120extern int exportfs_encode_fh(struct dentry *dentry, __u32 *fh, int *max_len,
121 int connectable);
122extern 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 */