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 * @pfd: [out] pointer to the file descriptor 61 * @dpinode: [out] pointer to the inode 62 * @pfile: [out] pointer to the file struct 63 * @name: [in] name of the "class" of the new file 64 * @fops [in] file operations for the new file 65 * @priv [in] private data for the new file (will be file's private_data) 66 * 67 * Creates a new file by hooking it on a single inode. This is useful for files 68 * that do not need to have a full-fledged inode in order to operate correctly. 69 * All the files created with anon_inode_getfd() will share a single inode, 70 * hence saving memory and avoiding code duplication for the file/inode/dentry 71 * setup. 72 */ 73 int anon_inode_getfd(int *pfd, struct inode **pinode, struct file **pfile, 74 const char *name, const struct file_operations *fops, 75 void *priv) 76 { 77 struct qstr this; 78 struct dentry *dentry; 79 struct file *file; 80 int error, fd; 81 82 if (IS_ERR(anon_inode_inode)) 83 return -ENODEV; 84 85 error = get_unused_fd(); 86 if (error < 0) 87 return error; 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; 123 file->f_version = 0; 124 file->private_data = priv; 125 126 fd_install(fd, file); 127 128 *pfd = fd; 129 *pinode = anon_inode_inode; 130 *pfile = file; 131 return 0; 132 133 err_dput: 134 dput(dentry); 135 err_put_unused_fd: 136 put_unused_fd(fd); 137 return error; 138 } 139 EXPORT_SYMBOL_GPL(anon_inode_getfd); 140 141 /* 142 * A single inode exists for all anon_inode files. Contrary to pipes, 143 * anon_inode inodes have no associated per-instance data, so we need 144 * only allocate one of them. 145 */ 146 static struct inode *anon_inode_mkinode(void) 147 { 148 struct inode *inode = new_inode(anon_inode_mnt->mnt_sb); 149 150 if (!inode) 151 return ERR_PTR(-ENOMEM); 152 153 inode->i_fop = &anon_inode_fops; 154 155 /* 156 * Mark the inode dirty from the very beginning, 157 * that way it will never be moved to the dirty 158 * list because mark_inode_dirty() will think 159 * that it already _is_ on the dirty list. 160 */ 161 inode->i_state = I_DIRTY; 162 inode->i_mode = S_IRUSR | S_IWUSR; 163 inode->i_uid = current->fsuid; 164 inode->i_gid = current->fsgid; 165 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; 166 return inode; 167 } 168 169 static int __init anon_inode_init(void) 170 { 171 int error; 172 173 error = register_filesystem(&anon_inode_fs_type); 174 if (error) 175 goto err_exit; 176 anon_inode_mnt = kern_mount(&anon_inode_fs_type); 177 if (IS_ERR(anon_inode_mnt)) { 178 error = PTR_ERR(anon_inode_mnt); 179 goto err_unregister_filesystem; 180 } 181 anon_inode_inode = anon_inode_mkinode(); 182 if (IS_ERR(anon_inode_inode)) { 183 error = PTR_ERR(anon_inode_inode); 184 goto err_mntput; 185 } 186 187 return 0; 188 189 err_mntput: 190 mntput(anon_inode_mnt); 191 err_unregister_filesystem: 192 unregister_filesystem(&anon_inode_fs_type); 193 err_exit: 194 panic(KERN_ERR "anon_inode_init() failed (%d)\n", error); 195 } 196 197 fs_initcall(anon_inode_init); 198 199