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 * nop .set_page_dirty method so that people can use .page_mkwrite on 57 * anon inodes. 58 */ 59 static int anon_set_page_dirty(struct page *page) 60 { 61 return 0; 62 }; 63 64 static const struct address_space_operations anon_aops = { 65 .set_page_dirty = anon_set_page_dirty, 66 }; 67 68 /** 69 * anon_inode_getfd - creates a new file instance by hooking it up to an 70 * anonymous inode, and a dentry that describe the "class" 71 * of the file 72 * 73 * @name: [in] name of the "class" of the new file 74 * @fops: [in] file operations for the new file 75 * @priv: [in] private data for the new file (will be file's private_data) 76 * @flags: [in] flags 77 * 78 * Creates a new file by hooking it on a single inode. This is useful for files 79 * that do not need to have a full-fledged inode in order to operate correctly. 80 * All the files created with anon_inode_getfd() will share a single inode, 81 * hence saving memory and avoiding code duplication for the file/inode/dentry 82 * setup. Returns new descriptor or -error. 83 */ 84 int anon_inode_getfd(const char *name, const struct file_operations *fops, 85 void *priv, int flags) 86 { 87 struct qstr this; 88 struct dentry *dentry; 89 struct file *file; 90 int error, fd; 91 92 if (IS_ERR(anon_inode_inode)) 93 return -ENODEV; 94 95 if (fops->owner && !try_module_get(fops->owner)) 96 return -ENOENT; 97 98 error = get_unused_fd_flags(flags); 99 if (error < 0) 100 goto err_module; 101 fd = error; 102 103 /* 104 * Link the inode to a directory entry by creating a unique name 105 * using the inode sequence number. 106 */ 107 error = -ENOMEM; 108 this.name = name; 109 this.len = strlen(name); 110 this.hash = 0; 111 dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this); 112 if (!dentry) 113 goto err_put_unused_fd; 114 115 /* 116 * We know the anon_inode inode count is always greater than zero, 117 * so we can avoid doing an igrab() and we can use an open-coded 118 * atomic_inc(). 119 */ 120 atomic_inc(&anon_inode_inode->i_count); 121 122 dentry->d_op = &anon_inodefs_dentry_operations; 123 /* Do not publish this dentry inside the global dentry hash table */ 124 dentry->d_flags &= ~DCACHE_UNHASHED; 125 d_instantiate(dentry, anon_inode_inode); 126 127 error = -ENFILE; 128 file = alloc_file(anon_inode_mnt, dentry, 129 FMODE_READ | FMODE_WRITE, fops); 130 if (!file) 131 goto err_dput; 132 file->f_mapping = anon_inode_inode->i_mapping; 133 134 file->f_pos = 0; 135 file->f_flags = O_RDWR | (flags & O_NONBLOCK); 136 file->f_version = 0; 137 file->private_data = priv; 138 139 fd_install(fd, file); 140 141 return fd; 142 143 err_dput: 144 dput(dentry); 145 err_put_unused_fd: 146 put_unused_fd(fd); 147 err_module: 148 module_put(fops->owner); 149 return error; 150 } 151 EXPORT_SYMBOL_GPL(anon_inode_getfd); 152 153 /* 154 * A single inode exists for all anon_inode files. Contrary to pipes, 155 * anon_inode inodes have no associated per-instance data, so we need 156 * only allocate one of them. 157 */ 158 static struct inode *anon_inode_mkinode(void) 159 { 160 struct inode *inode = new_inode(anon_inode_mnt->mnt_sb); 161 162 if (!inode) 163 return ERR_PTR(-ENOMEM); 164 165 inode->i_fop = &anon_inode_fops; 166 167 inode->i_mapping->a_ops = &anon_aops; 168 169 /* 170 * Mark the inode dirty from the very beginning, 171 * that way it will never be moved to the dirty 172 * list because mark_inode_dirty() will think 173 * that it already _is_ on the dirty list. 174 */ 175 inode->i_state = I_DIRTY; 176 inode->i_mode = S_IRUSR | S_IWUSR; 177 inode->i_uid = current_fsuid(); 178 inode->i_gid = current_fsgid(); 179 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; 180 return inode; 181 } 182 183 static int __init anon_inode_init(void) 184 { 185 int error; 186 187 error = register_filesystem(&anon_inode_fs_type); 188 if (error) 189 goto err_exit; 190 anon_inode_mnt = kern_mount(&anon_inode_fs_type); 191 if (IS_ERR(anon_inode_mnt)) { 192 error = PTR_ERR(anon_inode_mnt); 193 goto err_unregister_filesystem; 194 } 195 anon_inode_inode = anon_inode_mkinode(); 196 if (IS_ERR(anon_inode_inode)) { 197 error = PTR_ERR(anon_inode_inode); 198 goto err_mntput; 199 } 200 201 return 0; 202 203 err_mntput: 204 mntput(anon_inode_mnt); 205 err_unregister_filesystem: 206 unregister_filesystem(&anon_inode_fs_type); 207 err_exit: 208 panic(KERN_ERR "anon_inode_init() failed (%d)\n", error); 209 } 210 211 fs_initcall(anon_inode_init); 212 213