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
  28 /*
  29  * anon_inodefs_dname() is called from d_path().
  30  */
  31 static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
  32 {
  33         return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
  34                                 dentry->d_name.name);
  35 }
  36
  37 static const struct dentry_operations anon_inodefs_dentry_operations = {
  38         .d_dname        = anon_inodefs_dname,
  39 };
  40
  41 static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type,
  42                                 int flags, const char *dev_name, void *data)
  43 {
  44         struct dentry *root;
  45         root = mount_pseudo(fs_type, "anon_inode:", NULL,
  46                         &anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC);
  47         if (!IS_ERR(root)) {
  48                 struct super_block *s = root->d_sb;
  49                 anon_inode_inode = alloc_anon_inode(s);
  50                 if (IS_ERR(anon_inode_inode)) {
  51                         dput(root);
  52                         deactivate_locked_super(s);
  53                         root = ERR_CAST(anon_inode_inode);
  54                 }
  55         }
  56         return root;
  57 }
  58
  59 static struct file_system_type anon_inode_fs_type = {
  60         .name           = "anon_inodefs",
  61         .mount          = anon_inodefs_mount,
  62         .kill_sb        = kill_anon_super,
  63 };
  64
  65 /**
  66  * anon_inode_getfile - creates a new file instance by hooking it up to an
  67  *                      anonymous inode, and a dentry that describe the "class"
  68  *                      of the file
  69  *
  70  * @name:    [in]    name of the "class" of the new file
  71  * @fops:    [in]    file operations for the new file
  72  * @priv:    [in]    private data for the new file (will be file's private_data)
  73  * @flags:   [in]    flags
  74  *
  75  * Creates a new file by hooking it on a single inode. This is useful for files
  76  * that do not need to have a full-fledged inode in order to operate correctly.
  77  * All the files created with anon_inode_getfile() will share a single inode,
  78  * hence saving memory and avoiding code duplication for the file/inode/dentry
  79  * setup.  Returns the newly created file* or an error pointer.
  80  */
  81 struct file *anon_inode_getfile(const char *name,
  82                                 const struct file_operations *fops,
  83                                 void *priv, int flags)
  84 {
  85         struct qstr this;
  86         struct path path;
  87         struct file *file;
  88
  89         if (IS_ERR(anon_inode_inode))
  90                 return ERR_PTR(-ENODEV);
  91
  92         if (fops->owner && !try_module_get(fops->owner))
  93                 return ERR_PTR(-ENOENT);
  94
  95         /*
  96          * Link the inode to a directory entry by creating a unique name
  97          * using the inode sequence number.
  98          */
  99         file = ERR_PTR(-ENOMEM);
 100         this.name = name;
 101         this.len = strlen(name);
 102         this.hash = 0;
 103         path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this);
 104         if (!path.dentry)
 105                 goto err_module;
 106
 107         path.mnt = mntget(anon_inode_mnt);
 108         /*
 109          * We know the anon_inode inode count is always greater than zero,
 110          * so ihold() is safe.
 111          */
 112         ihold(anon_inode_inode);
 113
 114         d_instantiate(path.dentry, anon_inode_inode);
 115
 116         file = alloc_file(&path, OPEN_FMODE(flags), fops);
 117         if (IS_ERR(file))
 118                 goto err_dput;
 119         file->f_mapping = anon_inode_inode->i_mapping;
 120
 121         file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
 122         file->private_data = priv;
 123
 124         return file;
 125
 126 err_dput:
 127         path_put(&path);
 128 err_module:
 129         module_put(fops->owner);
 130         return file;
 131 }
 132 EXPORT_SYMBOL_GPL(anon_inode_getfile);
 133
 134 /**
 135  * anon_inode_getfd - creates a new file instance by hooking it up to an
 136  *                    anonymous inode, and a dentry that describe the "class"
 137  *                    of the file
 138  *
 139  * @name:    [in]    name of the "class" of the new file
 140  * @fops:    [in]    file operations for the new file
 141  * @priv:    [in]    private data for the new file (will be file's private_data)
 142  * @flags:   [in]    flags
 143  *
 144  * Creates a new file by hooking it on a single inode. This is useful for files
 145  * that do not need to have a full-fledged inode in order to operate correctly.
 146  * All the files created with anon_inode_getfd() will share a single inode,
 147  * hence saving memory and avoiding code duplication for the file/inode/dentry
 148  * setup.  Returns new descriptor or an error code.
 149  */
 150 int anon_inode_getfd(const char *name, const struct file_operations *fops,
 151                      void *priv, int flags)
 152 {
 153         int error, fd;
 154         struct file *file;
 155
 156         error = get_unused_fd_flags(flags);
 157         if (error < 0)
 158                 return error;
 159         fd = error;
 160
 161         file = anon_inode_getfile(name, fops, priv, flags);
 162         if (IS_ERR(file)) {
 163                 error = PTR_ERR(file);
 164                 goto err_put_unused_fd;
 165         }
 166         fd_install(fd, file);
 167
 168         return fd;
 169
 170 err_put_unused_fd:
 171         put_unused_fd(fd);
 172         return error;
 173 }
 174 EXPORT_SYMBOL_GPL(anon_inode_getfd);
 175
 176 static int __init anon_inode_init(void)
 177 {
 178         int error;
 179
 180         error = register_filesystem(&anon_inode_fs_type);
 181         if (error)
 182                 goto err_exit;
 183         anon_inode_mnt = kern_mount(&anon_inode_fs_type);
 184         if (IS_ERR(anon_inode_mnt)) {
 185                 error = PTR_ERR(anon_inode_mnt);
 186                 goto err_unregister_filesystem;
 187         }
 188         return 0;
 189
 190 err_unregister_filesystem:
 191         unregister_filesystem(&anon_inode_fs_type);
 192 err_exit:
 193         panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
 194 }
 195
 196 fs_initcall(anon_inode_init);
 197