| 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 | static const struct file_operations anon_inode_fops; |
| 28 | |
| 29 | /* |
| 30 | * anon_inodefs_dname() is called from d_path(). |
| 31 | */ |
| 32 | static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen) |
| 33 | { |
| 34 | return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s", |
| 35 | dentry->d_name.name); |
| 36 | } |
| 37 | |
| 38 | static const struct dentry_operations anon_inodefs_dentry_operations = { |
| 39 | .d_dname = anon_inodefs_dname, |
| 40 | }; |
| 41 | |
| 42 | /* |
| 43 | * nop .set_page_dirty method so that people can use .page_mkwrite on |
| 44 | * anon inodes. |
| 45 | */ |
| 46 | static int anon_set_page_dirty(struct page *page) |
| 47 | { |
| 48 | return 0; |
| 49 | }; |
| 50 | |
| 51 | static const struct address_space_operations anon_aops = { |
| 52 | .set_page_dirty = anon_set_page_dirty, |
| 53 | }; |
| 54 | |
| 55 | /* |
| 56 | * A single inode exists for all anon_inode files. Contrary to pipes, |
| 57 | * anon_inode inodes have no associated per-instance data, so we need |
| 58 | * only allocate one of them. |
| 59 | */ |
| 60 | static struct inode *anon_inode_mkinode(struct super_block *s) |
| 61 | { |
| 62 | struct inode *inode = new_inode_pseudo(s); |
| 63 | |
| 64 | if (!inode) |
| 65 | return ERR_PTR(-ENOMEM); |
| 66 | |
| 67 | inode->i_ino = get_next_ino(); |
| 68 | inode->i_fop = &anon_inode_fops; |
| 69 | |
| 70 | inode->i_mapping->a_ops = &anon_aops; |
| 71 | |
| 72 | /* |
| 73 | * Mark the inode dirty from the very beginning, |
| 74 | * that way it will never be moved to the dirty |
| 75 | * list because mark_inode_dirty() will think |
| 76 | * that it already _is_ on the dirty list. |
| 77 | */ |
| 78 | inode->i_state = I_DIRTY; |
| 79 | inode->i_mode = S_IRUSR | S_IWUSR; |
| 80 | inode->i_uid = current_fsuid(); |
| 81 | inode->i_gid = current_fsgid(); |
| 82 | inode->i_flags |= S_PRIVATE; |
| 83 | inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; |
| 84 | return inode; |
| 85 | } |
| 86 | |
| 87 | static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type, |
| 88 | int flags, const char *dev_name, void *data) |
| 89 | { |
| 90 | struct dentry *root; |
| 91 | root = mount_pseudo(fs_type, "anon_inode:", NULL, |
| 92 | &anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC); |
| 93 | if (!IS_ERR(root)) { |
| 94 | struct super_block *s = root->d_sb; |
| 95 | anon_inode_inode = anon_inode_mkinode(s); |
| 96 | if (IS_ERR(anon_inode_inode)) { |
| 97 | dput(root); |
| 98 | deactivate_locked_super(s); |
| 99 | root = ERR_CAST(anon_inode_inode); |
| 100 | } |
| 101 | } |
| 102 | return root; |
| 103 | } |
| 104 | |
| 105 | static struct file_system_type anon_inode_fs_type = { |
| 106 | .name = "anon_inodefs", |
| 107 | .mount = anon_inodefs_mount, |
| 108 | .kill_sb = kill_anon_super, |
| 109 | }; |
| 110 | |
| 111 | /** |
| 112 | * anon_inode_getfile - creates a new file instance by hooking it up to an |
| 113 | * anonymous inode, and a dentry that describe the "class" |
| 114 | * of the file |
| 115 | * |
| 116 | * @name: [in] name of the "class" of the new file |
| 117 | * @fops: [in] file operations for the new file |
| 118 | * @priv: [in] private data for the new file (will be file's private_data) |
| 119 | * @flags: [in] flags |
| 120 | * |
| 121 | * Creates a new file by hooking it on a single inode. This is useful for files |
| 122 | * that do not need to have a full-fledged inode in order to operate correctly. |
| 123 | * All the files created with anon_inode_getfile() will share a single inode, |
| 124 | * hence saving memory and avoiding code duplication for the file/inode/dentry |
| 125 | * setup. Returns the newly created file* or an error pointer. |
| 126 | */ |
| 127 | struct file *anon_inode_getfile(const char *name, |
| 128 | const struct file_operations *fops, |
| 129 | void *priv, int flags) |
| 130 | { |
| 131 | struct qstr this; |
| 132 | struct path path; |
| 133 | struct file *file; |
| 134 | |
| 135 | if (IS_ERR(anon_inode_inode)) |
| 136 | return ERR_PTR(-ENODEV); |
| 137 | |
| 138 | if (fops->owner && !try_module_get(fops->owner)) |
| 139 | return ERR_PTR(-ENOENT); |
| 140 | |
| 141 | /* |
| 142 | * Link the inode to a directory entry by creating a unique name |
| 143 | * using the inode sequence number. |
| 144 | */ |
| 145 | file = ERR_PTR(-ENOMEM); |
| 146 | this.name = name; |
| 147 | this.len = strlen(name); |
| 148 | this.hash = 0; |
| 149 | path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this); |
| 150 | if (!path.dentry) |
| 151 | goto err_module; |
| 152 | |
| 153 | path.mnt = mntget(anon_inode_mnt); |
| 154 | /* |
| 155 | * We know the anon_inode inode count is always greater than zero, |
| 156 | * so ihold() is safe. |
| 157 | */ |
| 158 | ihold(anon_inode_inode); |
| 159 | |
| 160 | d_instantiate(path.dentry, anon_inode_inode); |
| 161 | |
| 162 | file = alloc_file(&path, OPEN_FMODE(flags), fops); |
| 163 | if (IS_ERR(file)) |
| 164 | goto err_dput; |
| 165 | file->f_mapping = anon_inode_inode->i_mapping; |
| 166 | |
| 167 | file->f_flags = flags & (O_ACCMODE | O_NONBLOCK); |
| 168 | file->private_data = priv; |
| 169 | |
| 170 | return file; |
| 171 | |
| 172 | err_dput: |
| 173 | path_put(&path); |
| 174 | err_module: |
| 175 | module_put(fops->owner); |
| 176 | return file; |
| 177 | } |
| 178 | EXPORT_SYMBOL_GPL(anon_inode_getfile); |
| 179 | |
| 180 | /** |
| 181 | * anon_inode_getfd - creates a new file instance by hooking it up to an |
| 182 | * anonymous inode, and a dentry that describe the "class" |
| 183 | * of the file |
| 184 | * |
| 185 | * @name: [in] name of the "class" of the new file |
| 186 | * @fops: [in] file operations for the new file |
| 187 | * @priv: [in] private data for the new file (will be file's private_data) |
| 188 | * @flags: [in] flags |
| 189 | * |
| 190 | * Creates a new file by hooking it on a single inode. This is useful for files |
| 191 | * that do not need to have a full-fledged inode in order to operate correctly. |
| 192 | * All the files created with anon_inode_getfd() will share a single inode, |
| 193 | * hence saving memory and avoiding code duplication for the file/inode/dentry |
| 194 | * setup. Returns new descriptor or an error code. |
| 195 | */ |
| 196 | int anon_inode_getfd(const char *name, const struct file_operations *fops, |
| 197 | void *priv, int flags) |
| 198 | { |
| 199 | int error, fd; |
| 200 | struct file *file; |
| 201 | |
| 202 | error = get_unused_fd_flags(flags); |
| 203 | if (error < 0) |
| 204 | return error; |
| 205 | fd = error; |
| 206 | |
| 207 | file = anon_inode_getfile(name, fops, priv, flags); |
| 208 | if (IS_ERR(file)) { |
| 209 | error = PTR_ERR(file); |
| 210 | goto err_put_unused_fd; |
| 211 | } |
| 212 | fd_install(fd, file); |
| 213 | |
| 214 | return fd; |
| 215 | |
| 216 | err_put_unused_fd: |
| 217 | put_unused_fd(fd); |
| 218 | return error; |
| 219 | } |
| 220 | EXPORT_SYMBOL_GPL(anon_inode_getfd); |
| 221 | |
| 222 | static int __init anon_inode_init(void) |
| 223 | { |
| 224 | int error; |
| 225 | |
| 226 | error = register_filesystem(&anon_inode_fs_type); |
| 227 | if (error) |
| 228 | goto err_exit; |
| 229 | anon_inode_mnt = kern_mount(&anon_inode_fs_type); |
| 230 | if (IS_ERR(anon_inode_mnt)) { |
| 231 | error = PTR_ERR(anon_inode_mnt); |
| 232 | goto err_unregister_filesystem; |
| 233 | } |
| 234 | return 0; |
| 235 | |
| 236 | err_unregister_filesystem: |
| 237 | unregister_filesystem(&anon_inode_fs_type); |
| 238 | err_exit: |
| 239 | panic(KERN_ERR "anon_inode_init() failed (%d)\n", error); |
| 240 | } |
| 241 | |
| 242 | fs_initcall(anon_inode_init); |
| 243 | |