fs/anon_inodes.c

   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 static const struct file_operations anon_inode_fops;
  28
  29 static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type,
  30                                 int flags, const char *dev_name, void *data)
  31 {
  32         return mount_pseudo(fs_type, "anon_inode:", NULL, ANON_INODE_FS_MAGIC);
  33 }
  34
  35 /*
  36  * anon_inodefs_dname() is called from d_path().
  37  */
  38 static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
  39 {
  40         return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
  41                                 dentry->d_name.name);
  42 }
  43
  44 static struct file_system_type anon_inode_fs_type = {
  45         .name           = "anon_inodefs",
  46         .mount          = anon_inodefs_mount,
  47         .kill_sb        = kill_anon_super,
  48 };
  49 static const struct dentry_operations anon_inodefs_dentry_operations = {
  50         .d_dname        = anon_inodefs_dname,
  51 };
  52
  53 /*
  54  * nop .set_page_dirty method so that people can use .page_mkwrite on
  55  * anon inodes.
  56  */
  57 static int anon_set_page_dirty(struct page *page)
  58 {
  59         return 0;
  60 };
  61
  62 static const struct address_space_operations anon_aops = {
  63         .set_page_dirty = anon_set_page_dirty,
  64 };
  65
  66 /**
  67  * anon_inode_getfd - creates a new file instance by hooking it up to an
  68  *                    anonymous inode, and a dentry that describe the "class"
  69  *                    of the file
  70  *
  71  * @name:    [in]    name of the "class" of the new file
  72  * @fops:    [in]    file operations for the new file
  73  * @priv:    [in]    private data for the new file (will be file's private_data)
  74  * @flags:   [in]    flags
  75  *
  76  * Creates a new file by hooking it on a single inode. This is useful for files
  77  * that do not need to have a full-fledged inode in order to operate correctly.
  78  * All the files created with anon_inode_getfile() will share a single inode,
  79  * hence saving memory and avoiding code duplication for the file/inode/dentry
  80  * setup.  Returns the newly created file* or an error pointer.
  81  */
  82 struct file *anon_inode_getfile(const char *name,
  83                                 const struct file_operations *fops,
  84                                 void *priv, int flags)
  85 {
  86         struct qstr this;
  87         struct path path;
  88         struct file *file;
  89         int error;
  90
  91         if (IS_ERR(anon_inode_inode))
  92                 return ERR_PTR(-ENODEV);
  93
  94         if (fops->owner && !try_module_get(fops->owner))
  95                 return ERR_PTR(-ENOENT);
  96
  97         /*
  98          * Link the inode to a directory entry by creating a unique name
  99          * using the inode sequence number.
 100          */
 101         error = -ENOMEM;
 102         this.name = name;
 103         this.len = strlen(name);
 104         this.hash = 0;
 105         path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this);
 106         if (!path.dentry)
 107                 goto err_module;
 108
 109         path.mnt = mntget(anon_inode_mnt);
 110         /*
 111          * We know the anon_inode inode count is always greater than zero,
 112          * so ihold() is safe.
 113          */
 114         ihold(anon_inode_inode);
 115
 116         d_set_d_op(path.dentry, &anon_inodefs_dentry_operations);
 117         d_instantiate(path.dentry, anon_inode_inode);
 118
 119         error = -ENFILE;
 120         file = alloc_file(&path, OPEN_FMODE(flags), fops);
 121         if (!file)
 122                 goto err_dput;
 123         file->f_mapping = anon_inode_inode->i_mapping;
 124
 125         file->f_pos = 0;
 126         file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
 127         file->f_version = 0;
 128         file->private_data = priv;
 129
 130         return file;
 131
 132 err_dput:
 133         path_put(&path);
 134 err_module:
 135         module_put(fops->owner);
 136         return ERR_PTR(error);
 137 }
 138 EXPORT_SYMBOL_GPL(anon_inode_getfile);
 139
 140 /**
 141  * anon_inode_getfd - creates a new file instance by hooking it up to an
 142  *                    anonymous inode, and a dentry that describe the "class"
 143  *                    of the file
 144  *
 145  * @name:    [in]    name of the "class" of the new file
 146  * @fops:    [in]    file operations for the new file
 147  * @priv:    [in]    private data for the new file (will be file's private_data)
 148  * @flags:   [in]    flags
 149  *
 150  * Creates a new file by hooking it on a single inode. This is useful for files
 151  * that do not need to have a full-fledged inode in order to operate correctly.
 152  * All the files created with anon_inode_getfd() will share a single inode,
 153  * hence saving memory and avoiding code duplication for the file/inode/dentry
 154  * setup.  Returns new descriptor or an error code.
 155  */
 156 int anon_inode_getfd(const char *name, const struct file_operations *fops,
 157                      void *priv, int flags)
 158 {
 159         int error, fd;
 160         struct file *file;
 161
 162         error = get_unused_fd_flags(flags);
 163         if (error < 0)
 164                 return error;
 165         fd = error;
 166
 167         file = anon_inode_getfile(name, fops, priv, flags);
 168         if (IS_ERR(file)) {
 169                 error = PTR_ERR(file);
 170                 goto err_put_unused_fd;
 171         }
 172         fd_install(fd, file);
 173
 174         return fd;
 175
 176 err_put_unused_fd:
 177         put_unused_fd(fd);
 178         return error;
 179 }
 180 EXPORT_SYMBOL_GPL(anon_inode_getfd);
 181
 182 /*
 183  * A single inode exists for all anon_inode files. Contrary to pipes,
 184  * anon_inode inodes have no associated per-instance data, so we need
 185  * only allocate one of them.
 186  */
 187 static struct inode *anon_inode_mkinode(void)
 188 {
 189         struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
 190
 191         if (!inode)
 192                 return ERR_PTR(-ENOMEM);
 193
 194         inode->i_ino = get_next_ino();
 195         inode->i_fop = &anon_inode_fops;
 196
 197         inode->i_mapping->a_ops = &anon_aops;
 198
 199         /*
 200          * Mark the inode dirty from the very beginning,
 201          * that way it will never be moved to the dirty
 202          * list because mark_inode_dirty() will think
 203          * that it already _is_ on the dirty list.
 204          */
 205         inode->i_state = I_DIRTY;
 206         inode->i_mode = S_IRUSR | S_IWUSR;
 207         inode->i_uid = current_fsuid();
 208         inode->i_gid = current_fsgid();
 209         inode->i_flags |= S_PRIVATE;
 210         inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 211         return inode;
 212 }
 213
 214 static int __init anon_inode_init(void)
 215 {
 216         int error;
 217
 218         error = register_filesystem(&anon_inode_fs_type);
 219         if (error)
 220                 goto err_exit;
 221         anon_inode_mnt = kern_mount(&anon_inode_fs_type);
 222         if (IS_ERR(anon_inode_mnt)) {
 223                 error = PTR_ERR(anon_inode_mnt);
 224                 goto err_unregister_filesystem;
 225         }
 226         anon_inode_inode = anon_inode_mkinode();
 227         if (IS_ERR(anon_inode_inode)) {
 228                 error = PTR_ERR(anon_inode_inode);
 229                 goto err_mntput;
 230         }
 231
 232         return 0;
 233
 234 err_mntput:
 235         mntput(anon_inode_mnt);
 236 err_unregister_filesystem:
 237         unregister_filesystem(&anon_inode_fs_type);
 238 err_exit:
 239         panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
 240 }
 241
 242 fs_initcall(anon_inode_init);
 243