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 int anon_inodefs_get_sb(struct file_system_type *fs_type, int flags,
  30                                const char *dev_name, void *data,
  31                                struct vfsmount *mnt)
  32 {
  33         return get_sb_pseudo(fs_type, "anon_inode:", NULL, ANON_INODE_FS_MAGIC,
  34                              mnt);
  35 }
  36
  37 /*
  38  * anon_inodefs_dname() is called from d_path().
  39  */
  40 static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
  41 {
  42         return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
  43                                 dentry->d_name.name);
  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_dname        = anon_inodefs_dname,
  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_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(anon_inode_mnt->mnt_sb->s_root, &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 we can avoid doing an igrab() and we can use an open-coded
 115          * atomic_inc().
 116          */
 117         atomic_inc(&anon_inode_inode->i_count);
 118
 119         path.dentry->d_op = &anon_inodefs_dentry_operations;
 120         d_instantiate(path.dentry, anon_inode_inode);
 121
 122         error = -ENFILE;
 123         file = alloc_file(&path, OPEN_FMODE(flags), fops);
 124         if (!file)
 125                 goto err_dput;
 126         file->f_mapping = anon_inode_inode->i_mapping;
 127
 128         file->f_pos = 0;
 129         file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
 130         file->f_version = 0;
 131         file->private_data = priv;
 132
 133         return file;
 134
 135 err_dput:
 136         path_put(&path);
 137 err_module:
 138         module_put(fops->owner);
 139         return ERR_PTR(error);
 140 }
 141 EXPORT_SYMBOL_GPL(anon_inode_getfile);
 142
 143 /**
 144  * anon_inode_getfd - creates a new file instance by hooking it up to an
 145  *                    anonymous inode, and a dentry that describe the "class"
 146  *                    of the file
 147  *
 148  * @name:    [in]    name of the "class" of the new file
 149  * @fops:    [in]    file operations for the new file
 150  * @priv:    [in]    private data for the new file (will be file's private_data)
 151  * @flags:   [in]    flags
 152  *
 153  * Creates a new file by hooking it on a single inode. This is useful for files
 154  * that do not need to have a full-fledged inode in order to operate correctly.
 155  * All the files created with anon_inode_getfd() will share a single inode,
 156  * hence saving memory and avoiding code duplication for the file/inode/dentry
 157  * setup.  Returns new descriptor or an error code.
 158  */
 159 int anon_inode_getfd(const char *name, const struct file_operations *fops,
 160                      void *priv, int flags)
 161 {
 162         int error, fd;
 163         struct file *file;
 164
 165         error = get_unused_fd_flags(flags);
 166         if (error < 0)
 167                 return error;
 168         fd = error;
 169
 170         file = anon_inode_getfile(name, fops, priv, flags);
 171         if (IS_ERR(file)) {
 172                 error = PTR_ERR(file);
 173                 goto err_put_unused_fd;
 174         }
 175         fd_install(fd, file);
 176
 177         return fd;
 178
 179 err_put_unused_fd:
 180         put_unused_fd(fd);
 181         return error;
 182 }
 183 EXPORT_SYMBOL_GPL(anon_inode_getfd);
 184
 185 /*
 186  * A single inode exists for all anon_inode files. Contrary to pipes,
 187  * anon_inode inodes have no associated per-instance data, so we need
 188  * only allocate one of them.
 189  */
 190 static struct inode *anon_inode_mkinode(void)
 191 {
 192         struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
 193
 194         if (!inode)
 195                 return ERR_PTR(-ENOMEM);
 196
 197         inode->i_fop = &anon_inode_fops;
 198
 199         inode->i_mapping->a_ops = &anon_aops;
 200
 201         /*
 202          * Mark the inode dirty from the very beginning,
 203          * that way it will never be moved to the dirty
 204          * list because mark_inode_dirty() will think
 205          * that it already _is_ on the dirty list.
 206          */
 207         inode->i_state = I_DIRTY;
 208         inode->i_mode = S_IRUSR | S_IWUSR;
 209         inode->i_uid = current_fsuid();
 210         inode->i_gid = current_fsgid();
 211         inode->i_flags |= S_PRIVATE;
 212         inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 213         return inode;
 214 }
 215
 216 static int __init anon_inode_init(void)
 217 {
 218         int error;
 219
 220         error = register_filesystem(&anon_inode_fs_type);
 221         if (error)
 222                 goto err_exit;
 223         anon_inode_mnt = kern_mount(&anon_inode_fs_type);
 224         if (IS_ERR(anon_inode_mnt)) {
 225                 error = PTR_ERR(anon_inode_mnt);
 226                 goto err_unregister_filesystem;
 227         }
 228         anon_inode_inode = anon_inode_mkinode();
 229         if (IS_ERR(anon_inode_inode)) {
 230                 error = PTR_ERR(anon_inode_inode);
 231                 goto err_mntput;
 232         }
 233
 234         return 0;
 235
 236 err_mntput:
 237         mntput(anon_inode_mnt);
 238 err_unregister_filesystem:
 239         unregister_filesystem(&anon_inode_fs_type);
 240 err_exit:
 241         panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
 242 }
 243
 244 fs_initcall(anon_inode_init);
 245