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 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 * 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_getfd() will share a single inode, 67 * hence saving memory and avoiding code duplication for the file/inode/dentry 68 * setup. Returns new descriptor or -error. 69 */ 70 int anon_inode_getfd(const char *name, const struct file_operations *fops, 71 void *priv) 72 { 73 struct qstr this; 74 struct dentry *dentry; 75 struct file *file; 76 int error, fd; 77 78 if (IS_ERR(anon_inode_inode)) 79 return -ENODEV; 80 81 error = get_unused_fd(); 82 if (error < 0) 83 return error; 84 fd = error; 85 86 /* 87 * Link the inode to a directory entry by creating a unique name 88 * using the inode sequence number. 89 */ 90 error = -ENOMEM; 91 this.name = name; 92 this.len = strlen(name); 93 this.hash = 0; 94 dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this); 95 if (!dentry) 96 goto err_put_unused_fd; 97 98 /* 99 * We know the anon_inode inode count is always greater than zero, 100 * so we can avoid doing an igrab() and we can use an open-coded 101 * atomic_inc(). 102 */ 103 atomic_inc(&anon_inode_inode->i_count); 104 105 dentry->d_op = &anon_inodefs_dentry_operations; 106 /* Do not publish this dentry inside the global dentry hash table */ 107 dentry->d_flags &= ~DCACHE_UNHASHED; 108 d_instantiate(dentry, anon_inode_inode); 109 110 error = -ENFILE; 111 file = alloc_file(anon_inode_mnt, dentry, 112 FMODE_READ | FMODE_WRITE, fops); 113 if (!file) 114 goto err_dput; 115 file->f_mapping = anon_inode_inode->i_mapping; 116 117 file->f_pos = 0; 118 file->f_flags = O_RDWR; 119 file->f_version = 0; 120 file->private_data = priv; 121 122 fd_install(fd, file); 123 124 return fd; 125 126 err_dput: 127 dput(dentry); 128 err_put_unused_fd: 129 put_unused_fd(fd); 130 return error; 131 } 132 EXPORT_SYMBOL_GPL(anon_inode_getfd); 133 134 /* 135 * A single inode exists for all anon_inode files. Contrary to pipes, 136 * anon_inode inodes have no associated per-instance data, so we need 137 * only allocate one of them. 138 */ 139 static struct inode *anon_inode_mkinode(void) 140 { 141 struct inode *inode = new_inode(anon_inode_mnt->mnt_sb); 142 143 if (!inode) 144 return ERR_PTR(-ENOMEM); 145 146 inode->i_fop = &anon_inode_fops; 147 148 /* 149 * Mark the inode dirty from the very beginning, 150 * that way it will never be moved to the dirty 151 * list because mark_inode_dirty() will think 152 * that it already _is_ on the dirty list. 153 */ 154 inode->i_state = I_DIRTY; 155 inode->i_mode = S_IRUSR | S_IWUSR; 156 inode->i_uid = current->fsuid; 157 inode->i_gid = current->fsgid; 158 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; 159 return inode; 160 } 161 162 static int __init anon_inode_init(void) 163 { 164 int error; 165 166 error = register_filesystem(&anon_inode_fs_type); 167 if (error) 168 goto err_exit; 169 anon_inode_mnt = kern_mount(&anon_inode_fs_type); 170 if (IS_ERR(anon_inode_mnt)) { 171 error = PTR_ERR(anon_inode_mnt); 172 goto err_unregister_filesystem; 173 } 174 anon_inode_inode = anon_inode_mkinode(); 175 if (IS_ERR(anon_inode_inode)) { 176 error = PTR_ERR(anon_inode_inode); 177 goto err_mntput; 178 } 179 180 return 0; 181 182 err_mntput: 183 mntput(anon_inode_mnt); 184 err_unregister_filesystem: 185 unregister_filesystem(&anon_inode_fs_type); 186 err_exit: 187 panic(KERN_ERR "anon_inode_init() failed (%d)\n", error); 188 } 189 190 fs_initcall(anon_inode_init); 191 192