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/slab.h> 16 #include <linux/init.h> 17 #include <linux/fs.h> 18 #include <linux/mount.h> 19 #include <linux/module.h> 20 #include <linux/kernel.h> 21 #include <linux/magic.h> 22 #include <linux/anon_inodes.h> 23 24 #include <asm/uaccess.h> 25 26 static struct vfsmount *anon_inode_mnt __read_mostly; 27 static struct inode *anon_inode_inode; 28 static const struct file_operations anon_inode_fops; 29 30 static int anon_inodefs_get_sb(struct file_system_type *fs_type, int flags, 31 const char *dev_name, void *data, 32 struct vfsmount *mnt) 33 { 34 return get_sb_pseudo(fs_type, "anon_inode:", NULL, ANON_INODE_FS_MAGIC, 35 mnt); 36 } 37 38 static int anon_inodefs_delete_dentry(struct dentry *dentry) 39 { 40 /* 41 * We faked vfs to believe the dentry was hashed when we created it. 42 * Now we restore the flag so that dput() will work correctly. 43 */ 44 dentry->d_flags |= DCACHE_UNHASHED; 45 return 1; 46 } 47 48 static struct file_system_type anon_inode_fs_type = { 49 .name = "anon_inodefs", 50 .get_sb = anon_inodefs_get_sb, 51 .kill_sb = kill_anon_super, 52 }; 53 static const struct dentry_operations anon_inodefs_dentry_operations = { 54 .d_delete = anon_inodefs_delete_dentry, 55 }; 56 57 /* 58 * nop .set_page_dirty method so that people can use .page_mkwrite on 59 * anon inodes. 60 */ 61 static int anon_set_page_dirty(struct page *page) 62 { 63 return 0; 64 }; 65 66 static const struct address_space_operations anon_aops = { 67 .set_page_dirty = anon_set_page_dirty, 68 }; 69 70 /** 71 * anon_inode_getfd - creates a new file instance by hooking it up to an 72 * anonymous inode, and a dentry that describe the "class" 73 * of the file 74 * 75 * @name: [in] name of the "class" of the new file 76 * @fops: [in] file operations for the new file 77 * @priv: [in] private data for the new file (will be file's private_data) 78 * @flags: [in] flags 79 * 80 * Creates a new file by hooking it on a single inode. This is useful for files 81 * that do not need to have a full-fledged inode in order to operate correctly. 82 * All the files created with anon_inode_getfile() will share a single inode, 83 * hence saving memory and avoiding code duplication for the file/inode/dentry 84 * setup. Returns the newly created file* or an error pointer. 85 */ 86 struct file *anon_inode_getfile(const char *name, 87 const struct file_operations *fops, 88 void *priv, int flags) 89 { 90 struct qstr this; 91 struct dentry *dentry; 92 struct file *file; 93 int error; 94 95 if (IS_ERR(anon_inode_inode)) 96 return ERR_PTR(-ENODEV); 97 98 if (fops->owner && !try_module_get(fops->owner)) 99 return ERR_PTR(-ENOENT); 100 101 /* 102 * Link the inode to a directory entry by creating a unique name 103 * using the inode sequence number. 104 */ 105 error = -ENOMEM; 106 this.name = name; 107 this.len = strlen(name); 108 this.hash = 0; 109 dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this); 110 if (!dentry) 111 goto err_module; 112 113 /* 114 * We know the anon_inode inode count is always greater than zero, 115 * so we can avoid doing an igrab() and we can use an open-coded 116 * atomic_inc(). 117 */ 118 atomic_inc(&anon_inode_inode->i_count); 119 120 dentry->d_op = &anon_inodefs_dentry_operations; 121 /* Do not publish this dentry inside the global dentry hash table */ 122 dentry->d_flags &= ~DCACHE_UNHASHED; 123 d_instantiate(dentry, anon_inode_inode); 124 125 error = -ENFILE; 126 file = alloc_file(anon_inode_mnt, dentry, 127 FMODE_READ | FMODE_WRITE, fops); 128 if (!file) 129 goto err_dput; 130 file->f_mapping = anon_inode_inode->i_mapping; 131 132 file->f_pos = 0; 133 file->f_flags = O_RDWR | (flags & O_NONBLOCK); 134 file->f_version = 0; 135 file->private_data = priv; 136 137 return file; 138 139 err_dput: 140 dput(dentry); 141 err_module: 142 module_put(fops->owner); 143 return ERR_PTR(error); 144 } 145 EXPORT_SYMBOL_GPL(anon_inode_getfile); 146 147 /** 148 * anon_inode_getfd - creates a new file instance by hooking it up to an 149 * anonymous inode, and a dentry that describe the "class" 150 * of the file 151 * 152 * @name: [in] name of the "class" of the new file 153 * @fops: [in] file operations for the new file 154 * @priv: [in] private data for the new file (will be file's private_data) 155 * @flags: [in] flags 156 * 157 * Creates a new file by hooking it on a single inode. This is useful for files 158 * that do not need to have a full-fledged inode in order to operate correctly. 159 * All the files created with anon_inode_getfd() will share a single inode, 160 * hence saving memory and avoiding code duplication for the file/inode/dentry 161 * setup. Returns new descriptor or an error code. 162 */ 163 int anon_inode_getfd(const char *name, const struct file_operations *fops, 164 void *priv, int flags) 165 { 166 int error, fd; 167 struct file *file; 168 169 error = get_unused_fd_flags(flags); 170 if (error < 0) 171 return error; 172 fd = error; 173 174 file = anon_inode_getfile(name, fops, priv, flags); 175 if (IS_ERR(file)) { 176 error = PTR_ERR(file); 177 goto err_put_unused_fd; 178 } 179 fd_install(fd, file); 180 181 return fd; 182 183 err_put_unused_fd: 184 put_unused_fd(fd); 185 return error; 186 } 187 EXPORT_SYMBOL_GPL(anon_inode_getfd); 188 189 /* 190 * A single inode exists for all anon_inode files. Contrary to pipes, 191 * anon_inode inodes have no associated per-instance data, so we need 192 * only allocate one of them. 193 */ 194 static struct inode *anon_inode_mkinode(void) 195 { 196 struct inode *inode = new_inode(anon_inode_mnt->mnt_sb); 197 198 if (!inode) 199 return ERR_PTR(-ENOMEM); 200 201 inode->i_fop = &anon_inode_fops; 202 203 inode->i_mapping->a_ops = &anon_aops; 204 205 /* 206 * Mark the inode dirty from the very beginning, 207 * that way it will never be moved to the dirty 208 * list because mark_inode_dirty() will think 209 * that it already _is_ on the dirty list. 210 */ 211 inode->i_state = I_DIRTY; 212 inode->i_mode = S_IRUSR | S_IWUSR; 213 inode->i_uid = current_fsuid(); 214 inode->i_gid = current_fsgid(); 215 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; 216 return inode; 217 } 218 219 static int __init anon_inode_init(void) 220 { 221 int error; 222 223 error = register_filesystem(&anon_inode_fs_type); 224 if (error) 225 goto err_exit; 226 anon_inode_mnt = kern_mount(&anon_inode_fs_type); 227 if (IS_ERR(anon_inode_mnt)) { 228 error = PTR_ERR(anon_inode_mnt); 229 goto err_unregister_filesystem; 230 } 231 anon_inode_inode = anon_inode_mkinode(); 232 if (IS_ERR(anon_inode_inode)) { 233 error = PTR_ERR(anon_inode_inode); 234 goto err_mntput; 235 } 236 237 return 0; 238 239 err_mntput: 240 mntput(anon_inode_mnt); 241 err_unregister_filesystem: 242 unregister_filesystem(&anon_inode_fs_type); 243 err_exit: 244 panic(KERN_ERR "anon_inode_init() failed (%d)\n", error); 245 } 246 247 fs_initcall(anon_inode_init); 248 249