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_private - 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  *
  76  * Similar to anon_inode_getfile, but each file holds a single inode.
  77  *
  78  */
  79 struct file *anon_inode_getfile_private(const char *name,
  80                                         const struct file_operations *fops,
  81                                         void *priv, int flags)
  82 {
  83         struct qstr this;
  84         struct path path;
  85         struct file *file;
  86         struct inode *inode;
  87
  88         if (fops->owner && !try_module_get(fops->owner))
  89                 return ERR_PTR(-ENOENT);
  90
  91         inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
  92         if (IS_ERR(inode)) {
  93                 file = ERR_PTR(-ENOMEM);
  94                 goto err_module;
  95         }
  96
  97         /*
  98          * Link the inode to a directory entry by creating a unique name
  99          * using the inode sequence number.
 100          */
 101         file = ERR_PTR(-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         d_instantiate(path.dentry, inode);
 112
 113         file = alloc_file(&path, OPEN_FMODE(flags), fops);
 114         if (IS_ERR(file))
 115                 goto err_dput;
 116
 117         file->f_mapping = inode->i_mapping;
 118         file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
 119         file->private_data = priv;
 120
 121         return file;
 122
 123 err_dput:
 124         path_put(&path);
 125 err_module:
 126         module_put(fops->owner);
 127         return file;
 128 }
 129 EXPORT_SYMBOL_GPL(anon_inode_getfile_private);
 130
 131 /**
 132  * anon_inode_getfile - creates a new file instance by hooking it up to an
 133  *                      anonymous inode, and a dentry that describe the "class"
 134  *                      of the file
 135  *
 136  * @name:    [in]    name of the "class" of the new file
 137  * @fops:    [in]    file operations for the new file
 138  * @priv:    [in]    private data for the new file (will be file's private_data)
 139  * @flags:   [in]    flags
 140  *
 141  * Creates a new file by hooking it on a single inode. This is useful for files
 142  * that do not need to have a full-fledged inode in order to operate correctly.
 143  * All the files created with anon_inode_getfile() will share a single inode,
 144  * hence saving memory and avoiding code duplication for the file/inode/dentry
 145  * setup.  Returns the newly created file* or an error pointer.
 146  */
 147 struct file *anon_inode_getfile(const char *name,
 148                                 const struct file_operations *fops,
 149                                 void *priv, int flags)
 150 {
 151         struct qstr this;
 152         struct path path;
 153         struct file *file;
 154
 155         if (IS_ERR(anon_inode_inode))
 156                 return ERR_PTR(-ENODEV);
 157
 158         if (fops->owner && !try_module_get(fops->owner))
 159                 return ERR_PTR(-ENOENT);
 160
 161         /*
 162          * Link the inode to a directory entry by creating a unique name
 163          * using the inode sequence number.
 164          */
 165         file = ERR_PTR(-ENOMEM);
 166         this.name = name;
 167         this.len = strlen(name);
 168         this.hash = 0;
 169         path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this);
 170         if (!path.dentry)
 171                 goto err_module;
 172
 173         path.mnt = mntget(anon_inode_mnt);
 174         /*
 175          * We know the anon_inode inode count is always greater than zero,
 176          * so ihold() is safe.
 177          */
 178         ihold(anon_inode_inode);
 179
 180         d_instantiate(path.dentry, anon_inode_inode);
 181
 182         file = alloc_file(&path, OPEN_FMODE(flags), fops);
 183         if (IS_ERR(file))
 184                 goto err_dput;
 185         file->f_mapping = anon_inode_inode->i_mapping;
 186
 187         file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
 188         file->private_data = priv;
 189
 190         return file;
 191
 192 err_dput:
 193         path_put(&path);
 194 err_module:
 195         module_put(fops->owner);
 196         return file;
 197 }
 198 EXPORT_SYMBOL_GPL(anon_inode_getfile);
 199
 200 /**
 201  * anon_inode_getfd - creates a new file instance by hooking it up to an
 202  *                    anonymous inode, and a dentry that describe the "class"
 203  *                    of the file
 204  *
 205  * @name:    [in]    name of the "class" of the new file
 206  * @fops:    [in]    file operations for the new file
 207  * @priv:    [in]    private data for the new file (will be file's private_data)
 208  * @flags:   [in]    flags
 209  *
 210  * Creates a new file by hooking it on a single inode. This is useful for files
 211  * that do not need to have a full-fledged inode in order to operate correctly.
 212  * All the files created with anon_inode_getfd() will share a single inode,
 213  * hence saving memory and avoiding code duplication for the file/inode/dentry
 214  * setup.  Returns new descriptor or an error code.
 215  */
 216 int anon_inode_getfd(const char *name, const struct file_operations *fops,
 217                      void *priv, int flags)
 218 {
 219         int error, fd;
 220         struct file *file;
 221
 222         error = get_unused_fd_flags(flags);
 223         if (error < 0)
 224                 return error;
 225         fd = error;
 226
 227         file = anon_inode_getfile(name, fops, priv, flags);
 228         if (IS_ERR(file)) {
 229                 error = PTR_ERR(file);
 230                 goto err_put_unused_fd;
 231         }
 232         fd_install(fd, file);
 233
 234         return fd;
 235
 236 err_put_unused_fd:
 237         put_unused_fd(fd);
 238         return error;
 239 }
 240 EXPORT_SYMBOL_GPL(anon_inode_getfd);
 241
 242 static int __init anon_inode_init(void)
 243 {
 244         int error;
 245
 246         error = register_filesystem(&anon_inode_fs_type);
 247         if (error)
 248                 goto err_exit;
 249         anon_inode_mnt = kern_mount(&anon_inode_fs_type);
 250         if (IS_ERR(anon_inode_mnt)) {
 251                 error = PTR_ERR(anon_inode_mnt);
 252                 goto err_unregister_filesystem;
 253         }
 254         return 0;
 255
 256 err_unregister_filesystem:
 257         unregister_filesystem(&anon_inode_fs_type);
 258 err_exit:
 259         panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
 260 }
 261
 262 fs_initcall(anon_inode_init);
 263