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/file.h> 12 #include <linux/poll.h> 13 #include <linux/slab.h> 14 #include <linux/init.h> 15 #include <linux/fs.h> 16 #include <linux/mount.h> 17 #include <linux/module.h> 18 #include <linux/kernel.h> 19 #include <linux/magic.h> 20 #include <linux/anon_inodes.h> 21 22 #include <asm/uaccess.h> 23 24 static struct vfsmount *anon_inode_mnt __read_mostly; 25 static struct inode *anon_inode_inode; 26 static const struct file_operations anon_inode_fops; 27 28 static int anon_inodefs_get_sb(struct file_system_type *fs_type, int flags, 29 const char *dev_name, void *data, 30 struct vfsmount *mnt) 31 { 32 return get_sb_pseudo(fs_type, "anon_inode:", NULL, ANON_INODE_FS_MAGIC, 33 mnt); 34 } 35 36 static int anon_inodefs_delete_dentry(struct dentry *dentry) 37 { 38 /* 39 * We faked vfs to believe the dentry was hashed when we created it. 40 * Now we restore the flag so that dput() will work correctly. 41 */ 42 dentry->d_flags |= DCACHE_UNHASHED; 43 return 1; 44 } 45 46 static struct file_system_type anon_inode_fs_type = { 47 .name = "anon_inodefs", 48 .get_sb = anon_inodefs_get_sb, 49 .kill_sb = kill_anon_super, 50 }; 51 static const struct dentry_operations anon_inodefs_dentry_operations = { 52 .d_delete = anon_inodefs_delete_dentry, 53 }; 54 55 /** 56 * anon_inode_getfd - creates a new file instance by hooking it up to an 57 * anonymous inode, and a dentry that describe the "class" 58 * of the file 59 * 60 * @name: [in] name of the "class" of the new file 61 * @fops: [in] file operations for the new file 62 * @priv: [in] private data for the new file (will be file's private_data) 63 * @flags: [in] flags 64 * 65 * Creates a new file by hooking it on a single inode. This is useful for files 66 * that do not need to have a full-fledged inode in order to operate correctly. 67 * All the files created with anon_inode_getfd() will share a single inode, 68 * hence saving memory and avoiding code duplication for the file/inode/dentry 69 * setup. Returns new descriptor or -error. 70 */ 71 int anon_inode_getfd(const char *name, const struct file_operations *fops, 72 void *priv, int flags) 73 { 74 struct qstr this; 75 struct dentry *dentry; 76 struct file *file; 77 int error, fd; 78 79 if (IS_ERR(anon_inode_inode)) 80 return -ENODEV; 81 82 if (fops->owner && !try_module_get(fops->owner)) 83 return -ENOENT; 84 85 error = get_unused_fd_flags(flags); 86 if (error < 0) 87 goto err_module; 88 fd = error; 89 90 /* 91 * Link the inode to a directory entry by creating a unique name 92 * using the inode sequence number. 93 */ 94 error = -ENOMEM; 95 this.name = name; 96 this.len = strlen(name); 97 this.hash = 0; 98 dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this); 99 if (!dentry) 100 goto err_put_unused_fd; 101 102 /* 103 * We know the anon_inode inode count is always greater than zero, 104 * so we can avoid doing an igrab() and we can use an open-coded 105 * atomic_inc(). 106 */ 107 atomic_inc(&anon_inode_inode->i_count); 108 109 dentry->d_op = &anon_inodefs_dentry_operations; 110 /* Do not publish this dentry inside the global dentry hash table */ 111 dentry->d_flags &= ~DCACHE_UNHASHED; 112 d_instantiate(dentry, anon_inode_inode); 113 114 error = -ENFILE; 115 file = alloc_file(anon_inode_mnt, dentry, 116 FMODE_READ | FMODE_WRITE, fops); 117 if (!file) 118 goto err_dput; 119 file->f_mapping = anon_inode_inode->i_mapping; 120 121 file->f_pos = 0; 122 file->f_flags = O_RDWR | (flags & O_NONBLOCK); 123 file->f_version = 0; 124 file->private_data = priv; 125 126 fd_install(fd, file); 127 128 return fd; 129 130 err_dput: 131 dput(dentry); 132 err_put_unused_fd: 133 put_unused_fd(fd); 134 err_module: 135 module_put(fops->owner); 136 return error; 137 } 138 EXPORT_SYMBOL_GPL(anon_inode_getfd); 139 140 /* 141 * A single inode exists for all anon_inode files. Contrary to pipes, 142 * anon_inode inodes have no associated per-instance data, so we need 143 * only allocate one of them. 144 */ 145 static struct inode *anon_inode_mkinode(void) 146 { 147 struct inode *inode = new_inode(anon_inode_mnt->mnt_sb); 148 149 if (!inode) 150 return ERR_PTR(-ENOMEM); 151 152 inode->i_fop = &anon_inode_fops; 153 154 /* 155 * Mark the inode dirty from the very beginning, 156 * that way it will never be moved to the dirty 157 * list because mark_inode_dirty() will think 158 * that it already _is_ on the dirty list. 159 */ 160 inode->i_state = I_DIRTY; 161 inode->i_mode = S_IRUSR | S_IWUSR; 162 inode->i_uid = current_fsuid(); 163 inode->i_gid = current_fsgid(); 164 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; 165 return inode; 166 } 167 168 static int __init anon_inode_init(void) 169 { 170 int error; 171 172 error = register_filesystem(&anon_inode_fs_type); 173 if (error) 174 goto err_exit; 175 anon_inode_mnt = kern_mount(&anon_inode_fs_type); 176 if (IS_ERR(anon_inode_mnt)) { 177 error = PTR_ERR(anon_inode_mnt); 178 goto err_unregister_filesystem; 179 } 180 anon_inode_inode = anon_inode_mkinode(); 181 if (IS_ERR(anon_inode_inode)) { 182 error = PTR_ERR(anon_inode_inode); 183 goto err_mntput; 184 } 185 186 return 0; 187 188 err_mntput: 189 mntput(anon_inode_mnt); 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