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 struct dentry *root; 45 root = mount_pseudo(fs_type, "anon_inode:", NULL, 46 &anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC); 47 if (!IS_ERR(root)) { 48 struct super_block *s = root->d_sb; 49 anon_inode_inode = alloc_anon_inode(s); 50 if (IS_ERR(anon_inode_inode)) { 51 dput(root); 52 deactivate_locked_super(s); 53 root = ERR_CAST(anon_inode_inode); 54 } 55 } 56 return root; 57 } 58 59 static struct file_system_type anon_inode_fs_type = { 60 .name = "anon_inodefs", 61 .mount = anon_inodefs_mount, 62 .kill_sb = kill_anon_super, 63 }; 64 65 /** 66 * anon_inode_getfile - creates a new file instance by hooking it up to an 67 * anonymous inode, and a dentry that describe the "class" 68 * of the file 69 * 70 * @name: [in] name of the "class" of the new file 71 * @fops: [in] file operations for the new file 72 * @priv: [in] private data for the new file (will be file's private_data) 73 * @flags: [in] flags 74 * 75 * Creates a new file by hooking it on a single inode. This is useful for files 76 * that do not need to have a full-fledged inode in order to operate correctly. 77 * All the files created with anon_inode_getfile() will share a single inode, 78 * hence saving memory and avoiding code duplication for the file/inode/dentry 79 * setup. Returns the newly created file* or an error pointer. 80 */ 81 struct file *anon_inode_getfile(const char *name, 82 const struct file_operations *fops, 83 void *priv, int flags) 84 { 85 struct qstr this; 86 struct path path; 87 struct file *file; 88 89 if (IS_ERR(anon_inode_inode)) 90 return ERR_PTR(-ENODEV); 91 92 if (fops->owner && !try_module_get(fops->owner)) 93 return ERR_PTR(-ENOENT); 94 95 /* 96 * Link the inode to a directory entry by creating a unique name 97 * using the inode sequence number. 98 */ 99 file = ERR_PTR(-ENOMEM); 100 this.name = name; 101 this.len = strlen(name); 102 this.hash = 0; 103 path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this); 104 if (!path.dentry) 105 goto err_module; 106 107 path.mnt = mntget(anon_inode_mnt); 108 /* 109 * We know the anon_inode inode count is always greater than zero, 110 * so ihold() is safe. 111 */ 112 ihold(anon_inode_inode); 113 114 d_instantiate(path.dentry, anon_inode_inode); 115 116 file = alloc_file(&path, OPEN_FMODE(flags), fops); 117 if (IS_ERR(file)) 118 goto err_dput; 119 file->f_mapping = anon_inode_inode->i_mapping; 120 121 file->f_flags = flags & (O_ACCMODE | O_NONBLOCK); 122 file->private_data = priv; 123 124 return file; 125 126 err_dput: 127 path_put(&path); 128 err_module: 129 module_put(fops->owner); 130 return file; 131 } 132 EXPORT_SYMBOL_GPL(anon_inode_getfile); 133 134 /** 135 * anon_inode_getfd - creates a new file instance by hooking it up to an 136 * anonymous inode, and a dentry that describe the "class" 137 * of the file 138 * 139 * @name: [in] name of the "class" of the new file 140 * @fops: [in] file operations for the new file 141 * @priv: [in] private data for the new file (will be file's private_data) 142 * @flags: [in] flags 143 * 144 * Creates a new file by hooking it on a single inode. This is useful for files 145 * that do not need to have a full-fledged inode in order to operate correctly. 146 * All the files created with anon_inode_getfd() will share a single inode, 147 * hence saving memory and avoiding code duplication for the file/inode/dentry 148 * setup. Returns new descriptor or an error code. 149 */ 150 int anon_inode_getfd(const char *name, const struct file_operations *fops, 151 void *priv, int flags) 152 { 153 int error, fd; 154 struct file *file; 155 156 error = get_unused_fd_flags(flags); 157 if (error < 0) 158 return error; 159 fd = error; 160 161 file = anon_inode_getfile(name, fops, priv, flags); 162 if (IS_ERR(file)) { 163 error = PTR_ERR(file); 164 goto err_put_unused_fd; 165 } 166 fd_install(fd, file); 167 168 return fd; 169 170 err_put_unused_fd: 171 put_unused_fd(fd); 172 return error; 173 } 174 EXPORT_SYMBOL_GPL(anon_inode_getfd); 175 176 static int __init anon_inode_init(void) 177 { 178 int error; 179 180 error = register_filesystem(&anon_inode_fs_type); 181 if (error) 182 goto err_exit; 183 anon_inode_mnt = kern_mount(&anon_inode_fs_type); 184 if (IS_ERR(anon_inode_mnt)) { 185 error = PTR_ERR(anon_inode_mnt); 186 goto err_unregister_filesystem; 187 } 188 return 0; 189 190 err_unregister_filesystem: 191 unregister_filesystem(&anon_inode_fs_type); 192 err_exit: 193 panic(KERN_ERR "anon_inode_init() failed (%d)\n", error); 194 } 195 196 fs_initcall(anon_inode_init); 197 198