LXR linux/fs/anon

   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/file.h>
  12#include <linux/poll.h>
  13#include <linux/slab.h>
  14#include <linux/init.h>
  15#include <linux/fs.h>
  16#include <linux/mount.h>
  17#include <linux/module.h>
  18#include <linux/kernel.h>
  19#include <linux/magic.h>
  20#include <linux/anon_inodes.h>
  21
  22#include <asm/uaccess.h>
  23
  24static struct vfsmount *anon_inode_mnt __read_mostly;
  25static struct inode *anon_inode_inode;
  26static const struct file_operations anon_inode_fops;
  27
  28static int anon_inodefs_get_sb(struct file_system_type *fs_type, int flags,
  29                               const char *dev_name, void *data,
  30                               struct vfsmount *mnt)
  31{
  32        return get_sb_pseudo(fs_type, "anon_inode:", NULL, ANON_INODE_FS_MAGIC,
  33                             mnt);
  34}
  35
  36static int anon_inodefs_delete_dentry(struct dentry *dentry)
  37{
  38        /*
  39         * We faked vfs to believe the dentry was hashed when we created it.
  40         * Now we restore the flag so that dput() will work correctly.
  41         */
  42        dentry->d_flags |= DCACHE_UNHASHED;
  43        return 1;
  44}
  45
  46static 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};
  51static struct dentry_operations anon_inodefs_dentry_operations = {
  52        .d_delete       = anon_inodefs_delete_dentry,
  53};
  54
  55/**
  56 * anon_inode_getfd - creates a new file instance by hooking it up to an
  57 *                    anonymous inode, and a dentry that describe the "class"
  58 *                    of the file
  59 *
  60 * @name:    [in]    name of the "class" of the new file
  61 * @fops:    [in]    file operations for the new file
  62 * @priv:    [in]    private data for the new file (will be file's private_data)
  63 * @flags:   [in]    flags
  64 *
  65 * Creates a new file by hooking it on a single inode. This is useful for files
  66 * that do not need to have a full-fledged inode in order to operate correctly.
  67 * All the files created with anon_inode_getfd() will share a single inode,
  68 * hence saving memory and avoiding code duplication for the file/inode/dentry
  69 * setup.  Returns new descriptor or -error.
  70 */
  71int anon_inode_getfd(const char *name, const struct file_operations *fops,
  72                     void *priv, int flags)
  73{
  74        struct qstr this;
  75        struct dentry *dentry;
  76        struct file *file;
  77        int error, fd;
  78
  79        if (IS_ERR(anon_inode_inode))
  80                return -ENODEV;
  81
  82        error = get_unused_fd_flags(flags);
  83        if (error < 0)
  84                return error;
  85        fd = error;
  86
  87        /*
  88         * Link the inode to a directory entry by creating a unique name
  89         * using the inode sequence number.
  90         */
  91        error = -ENOMEM;
  92        this.name = name;
  93        this.len = strlen(name);
  94        this.hash = 0;
  95        dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
  96        if (!dentry)
  97                goto err_put_unused_fd;
  98
  99        /*
 100         * We know the anon_inode inode count is always greater than zero,
 101         * so we can avoid doing an igrab() and we can use an open-coded
 102         * atomic_inc().
 103         */
 104        atomic_inc(&anon_inode_inode->i_count);
 105
 106        dentry->d_op = &anon_inodefs_dentry_operations;
 107        /* Do not publish this dentry inside the global dentry hash table */
 108        dentry->d_flags &= ~DCACHE_UNHASHED;
 109        d_instantiate(dentry, anon_inode_inode);
 110
 111        error = -ENFILE;
 112        file = alloc_file(anon_inode_mnt, dentry,
 113                          FMODE_READ | FMODE_WRITE, fops);
 114        if (!file)
 115                goto err_dput;
 116        file->f_mapping = anon_inode_inode->i_mapping;
 117
 118        file->f_pos = 0;
 119        file->f_flags = O_RDWR | (flags & O_NONBLOCK);
 120        file->f_version = 0;
 121        file->private_data = priv;
 122
 123        fd_install(fd, file);
 124
 125        return fd;
 126
 127err_dput:
 128        dput(dentry);
 129err_put_unused_fd:
 130        put_unused_fd(fd);
 131        return error;
 132}
 133EXPORT_SYMBOL_GPL(anon_inode_getfd);
 134
 135/*
 136 * A single inode exists for all anon_inode files. Contrary to pipes,
 137 * anon_inode inodes have no associated per-instance data, so we need
 138 * only allocate one of them.
 139 */
 140static struct inode *anon_inode_mkinode(void)
 141{
 142        struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
 143
 144        if (!inode)
 145                return ERR_PTR(-ENOMEM);
 146
 147        inode->i_fop = &anon_inode_fops;
 148
 149        /*
 150         * Mark the inode dirty from the very beginning,
 151         * that way it will never be moved to the dirty
 152         * list because mark_inode_dirty() will think
 153         * that it already _is_ on the dirty list.
 154         */
 155        inode->i_state = I_DIRTY;
 156        inode->i_mode = S_IRUSR | S_IWUSR;
 157        inode->i_uid = current->fsuid;
 158        inode->i_gid = current->fsgid;
 159        inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 160        return inode;
 161}
 162
 163static int __init anon_inode_init(void)
 164{
 165        int error;
 166
 167        error = register_filesystem(&anon_inode_fs_type);
 168        if (error)
 169                goto err_exit;
 170        anon_inode_mnt = kern_mount(&anon_inode_fs_type);
 171        if (IS_ERR(anon_inode_mnt)) {
 172                error = PTR_ERR(anon_inode_mnt);
 173                goto err_unregister_filesystem;
 174        }
 175        anon_inode_inode = anon_inode_mkinode();
 176        if (IS_ERR(anon_inode_inode)) {
 177                error = PTR_ERR(anon_inode_inode);
 178                goto err_mntput;
 179        }
 180
 181        return 0;
 182
 183err_mntput:
 184        mntput(anon_inode_mnt);
 185err_unregister_filesystem:
 186        unregister_filesystem(&anon_inode_fs_type);
 187err_exit:
 188        panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
 189}
 190
 191fs_initcall(anon_inode_init);
 192
 193