LXR linux/fs/anon

   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 *  fs/anon_inodes.c
   4 *
   5 *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
   6 *
   7 *  Thanks to Arnd Bergmann for code review and suggestions.
   8 *  More changes for Thomas Gleixner suggestions.
   9 *
  10 */
  11
  12#include <linux/cred.h>
  13#include <linux/file.h>
  14#include <linux/poll.h>
  15#include <linux/sched.h>
  16#include <linux/init.h>
  17#include <linux/fs.h>
  18#include <linux/mount.h>
  19#include <linux/module.h>
  20#include <linux/kernel.h>
  21#include <linux/magic.h>
  22#include <linux/anon_inodes.h>
  23
  24#include <linux/uaccess.h>
  25
  26static struct vfsmount *anon_inode_mnt __read_mostly;
  27static struct inode *anon_inode_inode;
  28
  29/*
  30 * anon_inodefs_dname() is called from d_path().
  31 */
  32static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
  33{
  34        return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
  35                                dentry->d_name.name);
  36}
  37
  38static const struct dentry_operations anon_inodefs_dentry_operations = {
  39        .d_dname        = anon_inodefs_dname,
  40};
  41
  42static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type,
  43                                int flags, const char *dev_name, void *data)
  44{
  45        return mount_pseudo(fs_type, "anon_inode:", NULL,
  46                        &anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC);
  47}
  48
  49static struct file_system_type anon_inode_fs_type = {
  50        .name           = "anon_inodefs",
  51        .mount          = anon_inodefs_mount,
  52        .kill_sb        = kill_anon_super,
  53};
  54
  55/**
  56 * anon_inode_getfile - 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_getfile() will share a single inode,
  68 * hence saving memory and avoiding code duplication for the file/inode/dentry
  69 * setup.  Returns the newly created file* or an error pointer.
  70 */
  71struct file *anon_inode_getfile(const char *name,
  72                                const struct file_operations *fops,
  73                                void *priv, int flags)
  74{
  75        struct file *file;
  76
  77        if (IS_ERR(anon_inode_inode))
  78                return ERR_PTR(-ENODEV);
  79
  80        if (fops->owner && !try_module_get(fops->owner))
  81                return ERR_PTR(-ENOENT);
  82
  83        /*
  84         * We know the anon_inode inode count is always greater than zero,
  85         * so ihold() is safe.
  86         */
  87        ihold(anon_inode_inode);
  88        file = alloc_file_pseudo(anon_inode_inode, anon_inode_mnt, name,
  89                                 flags & (O_ACCMODE | O_NONBLOCK), fops);
  90        if (IS_ERR(file))
  91                goto err;
  92
  93        file->f_mapping = anon_inode_inode->i_mapping;
  94
  95        file->private_data = priv;
  96
  97        return file;
  98
  99err:
 100        iput(anon_inode_inode);
 101        module_put(fops->owner);
 102        return file;
 103}
 104EXPORT_SYMBOL_GPL(anon_inode_getfile);
 105
 106/**
 107 * anon_inode_getfd - creates a new file instance by hooking it up to an
 108 *                    anonymous inode, and a dentry that describe the "class"
 109 *                    of the file
 110 *
 111 * @name:    [in]    name of the "class" of the new file
 112 * @fops:    [in]    file operations for the new file
 113 * @priv:    [in]    private data for the new file (will be file's private_data)
 114 * @flags:   [in]    flags
 115 *
 116 * Creates a new file by hooking it on a single inode. This is useful for files
 117 * that do not need to have a full-fledged inode in order to operate correctly.
 118 * All the files created with anon_inode_getfd() will share a single inode,
 119 * hence saving memory and avoiding code duplication for the file/inode/dentry
 120 * setup.  Returns new descriptor or an error code.
 121 */
 122int anon_inode_getfd(const char *name, const struct file_operations *fops,
 123                     void *priv, int flags)
 124{
 125        int error, fd;
 126        struct file *file;
 127
 128        error = get_unused_fd_flags(flags);
 129        if (error < 0)
 130                return error;
 131        fd = error;
 132
 133        file = anon_inode_getfile(name, fops, priv, flags);
 134        if (IS_ERR(file)) {
 135                error = PTR_ERR(file);
 136                goto err_put_unused_fd;
 137        }
 138        fd_install(fd, file);
 139
 140        return fd;
 141
 142err_put_unused_fd:
 143        put_unused_fd(fd);
 144        return error;
 145}
 146EXPORT_SYMBOL_GPL(anon_inode_getfd);
 147
 148static int __init anon_inode_init(void)
 149{
 150        anon_inode_mnt = kern_mount(&anon_inode_fs_type);
 151        if (IS_ERR(anon_inode_mnt))
 152                panic("anon_inode_init() kernel mount failed (%ld)\n", PTR_ERR(anon_inode_mnt));
 153
 154        anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
 155        if (IS_ERR(anon_inode_inode))
 156                panic("anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(anon_inode_inode));
 157
 158        return 0;
 159}
 160
 161fs_initcall(anon_inode_init);
 162
 163