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1 | /* |
2 | * fs/anon_inodes.c |
3 | * |
4 | * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org> |
5 | * |
6 | * Thanks to Arnd Bergmann for code review and suggestions. |
7 | * More changes for Thomas Gleixner suggestions. |
8 | * |
9 | */ |
10 | |
11 | #include <linux/cred.h> |
12 | #include <linux/file.h> |
13 | #include <linux/poll.h> |
14 | #include <linux/sched.h> |
15 | #include <linux/init.h> |
16 | #include <linux/fs.h> |
17 | #include <linux/mount.h> |
18 | #include <linux/module.h> |
19 | #include <linux/kernel.h> |
20 | #include <linux/magic.h> |
21 | #include <linux/anon_inodes.h> |
22 | |
23 | #include <asm/uaccess.h> |
24 | |
25 | static struct vfsmount *anon_inode_mnt __read_mostly; |
26 | static struct inode *anon_inode_inode; |
27 | |
28 | /* |
29 | * anon_inodefs_dname() is called from d_path(). |
30 | */ |
31 | static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen) |
32 | { |
33 | return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s", |
34 | dentry->d_name.name); |
35 | } |
36 | |
37 | static const struct dentry_operations anon_inodefs_dentry_operations = { |
38 | .d_dname = anon_inodefs_dname, |
39 | }; |
40 | |
41 | static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type, |
42 | int flags, const char *dev_name, void *data) |
43 | { |
44 | return mount_pseudo(fs_type, "anon_inode:", NULL, |
45 | &anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC); |
46 | } |
47 | |
48 | static struct file_system_type anon_inode_fs_type = { |
49 | .name = "anon_inodefs", |
50 | .mount = anon_inodefs_mount, |
51 | .kill_sb = kill_anon_super, |
52 | }; |
53 | |
54 | /** |
55 | * anon_inode_getfile - creates a new file instance by hooking it up to an |
56 | * anonymous inode, and a dentry that describe the "class" |
57 | * of the file |
58 | * |
59 | * @name: [in] name of the "class" of the new file |
60 | * @fops: [in] file operations for the new file |
61 | * @priv: [in] private data for the new file (will be file's private_data) |
62 | * @flags: [in] flags |
63 | * |
64 | * Creates a new file by hooking it on a single inode. This is useful for files |
65 | * that do not need to have a full-fledged inode in order to operate correctly. |
66 | * All the files created with anon_inode_getfile() will share a single inode, |
67 | * hence saving memory and avoiding code duplication for the file/inode/dentry |
68 | * setup. Returns the newly created file* or an error pointer. |
69 | */ |
70 | struct file *anon_inode_getfile(const char *name, |
71 | const struct file_operations *fops, |
72 | void *priv, int flags) |
73 | { |
74 | struct qstr this; |
75 | struct path path; |
76 | struct file *file; |
77 | |
78 | if (IS_ERR(anon_inode_inode)) |
79 | return ERR_PTR(-ENODEV); |
80 | |
81 | if (fops->owner && !try_module_get(fops->owner)) |
82 | return ERR_PTR(-ENOENT); |
83 | |
84 | /* |
85 | * Link the inode to a directory entry by creating a unique name |
86 | * using the inode sequence number. |
87 | */ |
88 | file = ERR_PTR(-ENOMEM); |
89 | this.name = name; |
90 | this.len = strlen(name); |
91 | this.hash = 0; |
92 | path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this); |
93 | if (!path.dentry) |
94 | goto err_module; |
95 | |
96 | path.mnt = mntget(anon_inode_mnt); |
97 | /* |
98 | * We know the anon_inode inode count is always greater than zero, |
99 | * so ihold() is safe. |
100 | */ |
101 | ihold(anon_inode_inode); |
102 | |
103 | d_instantiate(path.dentry, anon_inode_inode); |
104 | |
105 | file = alloc_file(&path, OPEN_FMODE(flags), fops); |
106 | if (IS_ERR(file)) |
107 | goto err_dput; |
108 | file->f_mapping = anon_inode_inode->i_mapping; |
109 | |
110 | file->f_flags = flags & (O_ACCMODE | O_NONBLOCK); |
111 | file->private_data = priv; |
112 | |
113 | return file; |
114 | |
115 | err_dput: |
116 | path_put(&path); |
117 | err_module: |
118 | module_put(fops->owner); |
119 | return file; |
120 | } |
121 | EXPORT_SYMBOL_GPL(anon_inode_getfile); |
122 | |
123 | /** |
124 | * anon_inode_getfd - creates a new file instance by hooking it up to an |
125 | * anonymous inode, and a dentry that describe the "class" |
126 | * of the file |
127 | * |
128 | * @name: [in] name of the "class" of the new file |
129 | * @fops: [in] file operations for the new file |
130 | * @priv: [in] private data for the new file (will be file's private_data) |
131 | * @flags: [in] flags |
132 | * |
133 | * Creates a new file by hooking it on a single inode. This is useful for files |
134 | * that do not need to have a full-fledged inode in order to operate correctly. |
135 | * All the files created with anon_inode_getfd() will share a single inode, |
136 | * hence saving memory and avoiding code duplication for the file/inode/dentry |
137 | * setup. Returns new descriptor or an error code. |
138 | */ |
139 | int anon_inode_getfd(const char *name, const struct file_operations *fops, |
140 | void *priv, int flags) |
141 | { |
142 | int error, fd; |
143 | struct file *file; |
144 | |
145 | error = get_unused_fd_flags(flags); |
146 | if (error < 0) |
147 | return error; |
148 | fd = error; |
149 | |
150 | file = anon_inode_getfile(name, fops, priv, flags); |
151 | if (IS_ERR(file)) { |
152 | error = PTR_ERR(file); |
153 | goto err_put_unused_fd; |
154 | } |
155 | fd_install(fd, file); |
156 | |
157 | return fd; |
158 | |
159 | err_put_unused_fd: |
160 | put_unused_fd(fd); |
161 | return error; |
162 | } |
163 | EXPORT_SYMBOL_GPL(anon_inode_getfd); |
164 | |
165 | static int __init anon_inode_init(void) |
166 | { |
167 | anon_inode_mnt = kern_mount(&anon_inode_fs_type); |
168 | if (IS_ERR(anon_inode_mnt)) |
169 | panic("anon_inode_init() kernel mount failed (%ld)\n", PTR_ERR(anon_inode_mnt)); |
170 | |
171 | anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb); |
172 | if (IS_ERR(anon_inode_inode)) |
173 | panic("anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(anon_inode_inode)); |
174 | |
175 | return 0; |
176 | } |
177 | |
178 | fs_initcall(anon_inode_init); |
179 | |
180 |
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