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 /*
  30  * anon_inodefs_dname() is called from d_path().
  31  */
  32 static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
  33 {
  34         return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
  35                                 dentry->d_name.name);
  36 }
  37
  38 static const struct dentry_operations anon_inodefs_dentry_operations = {
  39         .d_dname        = anon_inodefs_dname,
  40 };
  41
  42 static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type,
  43                                 int flags, const char *dev_name, void *data)
  44 {
  45         return mount_pseudo(fs_type, "anon_inode:", NULL,
  46                         &anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC);
  47 }
  48
  49 static struct file_system_type anon_inode_fs_type = {
  50         .name           = "anon_inodefs",
  51         .mount          = anon_inodefs_mount,
  52         .kill_sb        = kill_anon_super,
  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_getfile - 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_getfile() will share a single inode,
  81  * hence saving memory and avoiding code duplication for the file/inode/dentry
  82  * setup.  Returns the newly created file* or an error pointer.
  83  */
  84 struct file *anon_inode_getfile(const char *name,
  85                                 const struct file_operations *fops,
  86                                 void *priv, int flags)
  87 {
  88         struct qstr this;
  89         struct path path;
  90         struct file *file;
  91         int error;
  92
  93         if (IS_ERR(anon_inode_inode))
  94                 return ERR_PTR(-ENODEV);
  95
  96         if (fops->owner && !try_module_get(fops->owner))
  97                 return ERR_PTR(-ENOENT);
  98
  99         /*
 100          * Link the inode to a directory entry by creating a unique name
 101          * using the inode sequence number.
 102          */
 103         error = -ENOMEM;
 104         this.name = name;
 105         this.len = strlen(name);
 106         this.hash = 0;
 107         path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this);
 108         if (!path.dentry)
 109                 goto err_module;
 110
 111         path.mnt = mntget(anon_inode_mnt);
 112         /*
 113          * We know the anon_inode inode count is always greater than zero,
 114          * so ihold() is safe.
 115          */
 116         ihold(anon_inode_inode);
 117
 118         d_instantiate(path.dentry, anon_inode_inode);
 119
 120         error = -ENFILE;
 121         file = alloc_file(&path, OPEN_FMODE(flags), fops);
 122         if (!file)
 123                 goto err_dput;
 124         file->f_mapping = anon_inode_inode->i_mapping;
 125
 126         file->f_pos = 0;
 127         file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
 128         file->f_version = 0;
 129         file->private_data = priv;
 130
 131         return file;
 132
 133 err_dput:
 134         path_put(&path);
 135 err_module:
 136         module_put(fops->owner);
 137         return ERR_PTR(error);
 138 }
 139 EXPORT_SYMBOL_GPL(anon_inode_getfile);
 140
 141 /**
 142  * anon_inode_getfd - creates a new file instance by hooking it up to an
 143  *                    anonymous inode, and a dentry that describe the "class"
 144  *                    of the file
 145  *
 146  * @name:    [in]    name of the "class" of the new file
 147  * @fops:    [in]    file operations for the new file
 148  * @priv:    [in]    private data for the new file (will be file's private_data)
 149  * @flags:   [in]    flags
 150  *
 151  * Creates a new file by hooking it on a single inode. This is useful for files
 152  * that do not need to have a full-fledged inode in order to operate correctly.
 153  * All the files created with anon_inode_getfd() will share a single inode,
 154  * hence saving memory and avoiding code duplication for the file/inode/dentry
 155  * setup.  Returns new descriptor or an error code.
 156  */
 157 int anon_inode_getfd(const char *name, const struct file_operations *fops,
 158                      void *priv, int flags)
 159 {
 160         int error, fd;
 161         struct file *file;
 162
 163         error = get_unused_fd_flags(flags);
 164         if (error < 0)
 165                 return error;
 166         fd = error;
 167
 168         file = anon_inode_getfile(name, fops, priv, flags);
 169         if (IS_ERR(file)) {
 170                 error = PTR_ERR(file);
 171                 goto err_put_unused_fd;
 172         }
 173         fd_install(fd, file);
 174
 175         return fd;
 176
 177 err_put_unused_fd:
 178         put_unused_fd(fd);
 179         return error;
 180 }
 181 EXPORT_SYMBOL_GPL(anon_inode_getfd);
 182
 183 /*
 184  * A single inode exists for all anon_inode files. Contrary to pipes,
 185  * anon_inode inodes have no associated per-instance data, so we need
 186  * only allocate one of them.
 187  */
 188 static struct inode *anon_inode_mkinode(void)
 189 {
 190         struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
 191
 192         if (!inode)
 193                 return ERR_PTR(-ENOMEM);
 194
 195         inode->i_ino = get_next_ino();
 196         inode->i_fop = &anon_inode_fops;
 197
 198         inode->i_mapping->a_ops = &anon_aops;
 199
 200         /*
 201          * Mark the inode dirty from the very beginning,
 202          * that way it will never be moved to the dirty
 203          * list because mark_inode_dirty() will think
 204          * that it already _is_ on the dirty list.
 205          */
 206         inode->i_state = I_DIRTY;
 207         inode->i_mode = S_IRUSR | S_IWUSR;
 208         inode->i_uid = current_fsuid();
 209         inode->i_gid = current_fsgid();
 210         inode->i_flags |= S_PRIVATE;
 211         inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 212         return inode;
 213 }
 214
 215 static int __init anon_inode_init(void)
 216 {
 217         int error;
 218
 219         error = register_filesystem(&anon_inode_fs_type);
 220         if (error)
 221                 goto err_exit;
 222         anon_inode_mnt = kern_mount(&anon_inode_fs_type);
 223         if (IS_ERR(anon_inode_mnt)) {
 224                 error = PTR_ERR(anon_inode_mnt);
 225                 goto err_unregister_filesystem;
 226         }
 227         anon_inode_inode = anon_inode_mkinode();
 228         if (IS_ERR(anon_inode_inode)) {
 229                 error = PTR_ERR(anon_inode_inode);
 230                 goto err_mntput;
 231         }
 232
 233         return 0;
 234
 235 err_mntput:
 236         mntput_long(anon_inode_mnt);
 237 err_unregister_filesystem:
 238         unregister_filesystem(&anon_inode_fs_type);
 239 err_exit:
 240         panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
 241 }
 242
 243 fs_initcall(anon_inode_init);
 244