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/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 <linux/uaccess.h>
  24
  25static struct vfsmount *anon_inode_mnt __read_mostly;
  26static struct inode *anon_inode_inode;
  27
  28/*
  29 * anon_inodefs_dname() is called from d_path().
  30 */
  31static 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
  37static const struct dentry_operations anon_inodefs_dentry_operations = {
  38        .d_dname        = anon_inodefs_dname,
  39};
  40
  41static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type,
  42                                int flags, const char *dev_name, void *data)
  43{
  44        return mount_pseudo(fs_type, "anon_inode:", NULL,
  45                        &anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC);
  46}
  47
  48static struct file_system_type anon_inode_fs_type = {
  49        .name           = "anon_inodefs",
  50        .mount          = anon_inodefs_mount,
  51        .kill_sb        = kill_anon_super,
  52};
  53
  54/**
  55 * anon_inode_getfile - creates a new file instance by hooking it up to an
  56 *                      anonymous inode, and a dentry that describe the "class"
  57 *                      of the file
  58 *
  59 * @name:    [in]    name of the "class" of the new file
  60 * @fops:    [in]    file operations for the new file
  61 * @priv:    [in]    private data for the new file (will be file's private_data)
  62 * @flags:   [in]    flags
  63 *
  64 * Creates a new file by hooking it on a single inode. This is useful for files
  65 * that do not need to have a full-fledged inode in order to operate correctly.
  66 * All the files created with anon_inode_getfile() will share a single inode,
  67 * hence saving memory and avoiding code duplication for the file/inode/dentry
  68 * setup.  Returns the newly created file* or an error pointer.
  69 */
  70struct file *anon_inode_getfile(const char *name,
  71                                const struct file_operations *fops,
  72                                void *priv, int flags)
  73{
  74        struct file *file;
  75
  76        if (IS_ERR(anon_inode_inode))
  77                return ERR_PTR(-ENODEV);
  78
  79        if (fops->owner && !try_module_get(fops->owner))
  80                return ERR_PTR(-ENOENT);
  81
  82        /*
  83         * We know the anon_inode inode count is always greater than zero,
  84         * so ihold() is safe.
  85         */
  86        ihold(anon_inode_inode);
  87        file = alloc_file_pseudo(anon_inode_inode, anon_inode_mnt, name,
  88                                 flags & (O_ACCMODE | O_NONBLOCK), fops);
  89        if (IS_ERR(file))
  90                goto err;
  91
  92        file->f_mapping = anon_inode_inode->i_mapping;
  93
  94        file->private_data = priv;
  95
  96        return file;
  97
  98err:
  99        iput(anon_inode_inode);
 100        module_put(fops->owner);
 101        return file;
 102}
 103EXPORT_SYMBOL_GPL(anon_inode_getfile);
 104
 105/**
 106 * anon_inode_getfd - creates a new file instance by hooking it up to an
 107 *                    anonymous inode, and a dentry that describe the "class"
 108 *                    of the file
 109 *
 110 * @name:    [in]    name of the "class" of the new file
 111 * @fops:    [in]    file operations for the new file
 112 * @priv:    [in]    private data for the new file (will be file's private_data)
 113 * @flags:   [in]    flags
 114 *
 115 * Creates a new file by hooking it on a single inode. This is useful for files
 116 * that do not need to have a full-fledged inode in order to operate correctly.
 117 * All the files created with anon_inode_getfd() will share a single inode,
 118 * hence saving memory and avoiding code duplication for the file/inode/dentry
 119 * setup.  Returns new descriptor or an error code.
 120 */
 121int anon_inode_getfd(const char *name, const struct file_operations *fops,
 122                     void *priv, int flags)
 123{
 124        int error, fd;
 125        struct file *file;
 126
 127        error = get_unused_fd_flags(flags);
 128        if (error < 0)
 129                return error;
 130        fd = error;
 131
 132        file = anon_inode_getfile(name, fops, priv, flags);
 133        if (IS_ERR(file)) {
 134                error = PTR_ERR(file);
 135                goto err_put_unused_fd;
 136        }
 137        fd_install(fd, file);
 138
 139        return fd;
 140
 141err_put_unused_fd:
 142        put_unused_fd(fd);
 143        return error;
 144}
 145EXPORT_SYMBOL_GPL(anon_inode_getfd);
 146
 147static int __init anon_inode_init(void)
 148{
 149        anon_inode_mnt = kern_mount(&anon_inode_fs_type);
 150        if (IS_ERR(anon_inode_mnt))
 151                panic("anon_inode_init() kernel mount failed (%ld)\n", PTR_ERR(anon_inode_mnt));
 152
 153        anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
 154        if (IS_ERR(anon_inode_inode))
 155                panic("anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(anon_inode_inode));
 156
 157        return 0;
 158}
 159
 160fs_initcall(anon_inode_init);
 161
 162