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 and
  57 *                    anonymous inode, and a dentry that describe the "class"
  58 *                    of the file
  59 *
  60 * @pfd:     [out]   pointer to the file descriptor
  61 * @dpinode: [out]   pointer to the inode
  62 * @pfile:   [out]   pointer to the file struct
  63 * @name:    [in]    name of the "class" of the new file
  64 * @fops     [in]    file operations for the new file
  65 * @priv     [in]    private data for the new file (will be file's private_data)
  66 *
  67 * Creates a new file by hooking it on a single inode. This is useful for files
  68 * that do not need to have a full-fledged inode in order to operate correctly.
  69 * All the files created with anon_inode_getfd() will share a single inode, by
  70 * hence saving memory and avoiding code duplication for the file/inode/dentry
  71 * setup.
  72 */
  73int anon_inode_getfd(int *pfd, struct inode **pinode, struct file **pfile,
  74                     const char *name, const struct file_operations *fops,
  75                     void *priv)
  76{
  77        struct qstr this;
  78        struct dentry *dentry;
  79        struct inode *inode;
  80        struct file *file;
  81        int error, fd;
  82
  83        if (IS_ERR(anon_inode_inode))
  84                return -ENODEV;
  85        file = get_empty_filp();
  86        if (!file)
  87                return -ENFILE;
  88
  89        inode = igrab(anon_inode_inode);
  90        if (IS_ERR(inode)) {
  91                error = PTR_ERR(inode);
  92                goto err_put_filp;
  93        }
  94
  95        error = get_unused_fd();
  96        if (error < 0)
  97                goto err_iput;
  98        fd = error;
  99
 100        /*
 101         * Link the inode to a directory entry by creating a unique name
 102         * using the inode sequence number.
 103         */
 104        error = -ENOMEM;
 105        this.name = name;
 106        this.len = strlen(name);
 107        this.hash = 0;
 108        dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
 109        if (!dentry)
 110                goto err_put_unused_fd;
 111        dentry->d_op = &anon_inodefs_dentry_operations;
 112        /* Do not publish this dentry inside the global dentry hash table */
 113        dentry->d_flags &= ~DCACHE_UNHASHED;
 114        d_instantiate(dentry, inode);
 115
 116        file->f_path.mnt = mntget(anon_inode_mnt);
 117        file->f_path.dentry = dentry;
 118        file->f_mapping = inode->i_mapping;
 119
 120        file->f_pos = 0;
 121        file->f_flags = O_RDWR;
 122        file->f_op = fops;
 123        file->f_mode = FMODE_READ | FMODE_WRITE;
 124        file->f_version = 0;
 125        file->private_data = priv;
 126
 127        fd_install(fd, file);
 128
 129        *pfd = fd;
 130        *pinode = inode;
 131        *pfile = file;
 132        return 0;
 133
 134err_put_unused_fd:
 135        put_unused_fd(fd);
 136err_iput:
 137        iput(inode);
 138err_put_filp:
 139        put_filp(file);
 140        return error;
 141}
 142
 143/*
 144 * A single inode exist for all anon_inode files. Contrary to pipes,
 145 * anon_inode inodes has no per-instance data associated, so we can avoid
 146 * the allocation of multiple of them.
 147 */
 148static struct inode *anon_inode_mkinode(void)
 149{
 150        struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
 151
 152        if (!inode)
 153                return ERR_PTR(-ENOMEM);
 154
 155        inode->i_fop = &anon_inode_fops;
 156
 157        /*
 158         * Mark the inode dirty from the very beginning,
 159         * that way it will never be moved to the dirty
 160         * list because mark_inode_dirty() will think
 161         * that it already _is_ on the dirty list.
 162         */
 163        inode->i_state = I_DIRTY;
 164        inode->i_mode = S_IRUSR | S_IWUSR;
 165        inode->i_uid = current->fsuid;
 166        inode->i_gid = current->fsgid;
 167        inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 168        return inode;
 169}
 170
 171static int __init anon_inode_init(void)
 172{
 173        int error;
 174
 175        error = register_filesystem(&anon_inode_fs_type);
 176        if (error)
 177                goto err_exit;
 178        anon_inode_mnt = kern_mount(&anon_inode_fs_type);
 179        if (IS_ERR(anon_inode_mnt)) {
 180                error = PTR_ERR(anon_inode_mnt);
 181                goto err_unregister_filesystem;
 182        }
 183        anon_inode_inode = anon_inode_mkinode();
 184        if (IS_ERR(anon_inode_inode)) {
 185                error = PTR_ERR(anon_inode_inode);
 186                goto err_mntput;
 187        }
 188
 189        return 0;
 190
 191err_mntput:
 192        mntput(anon_inode_mnt);
 193err_unregister_filesystem:
 194        unregister_filesystem(&anon_inode_fs_type);
 195err_exit:
 196        panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
 197}
 198
 199fs_initcall(anon_inode_init);
 200
 201