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#include <linux/pseudo_fs.h>
  24
  25#include <linux/uaccess.h>
  26
  27static struct vfsmount *anon_inode_mnt __read_mostly;
  28static struct inode *anon_inode_inode;
  29
  30/*
  31 * anon_inodefs_dname() is called from d_path().
  32 */
  33static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
  34{
  35        return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
  36                                dentry->d_name.name);
  37}
  38
  39static const struct dentry_operations anon_inodefs_dentry_operations = {
  40        .d_dname        = anon_inodefs_dname,
  41};
  42
  43static int anon_inodefs_init_fs_context(struct fs_context *fc)
  44{
  45        struct pseudo_fs_context *ctx = init_pseudo(fc, ANON_INODE_FS_MAGIC);
  46        if (!ctx)
  47                return -ENOMEM;
  48        ctx->dops = &anon_inodefs_dentry_operations;
  49        return 0;
  50}
  51
  52static struct file_system_type anon_inode_fs_type = {
  53        .name           = "anon_inodefs",
  54        .init_fs_context = anon_inodefs_init_fs_context,
  55        .kill_sb        = kill_anon_super,
  56};
  57
  58/**
  59 * anon_inode_getfile - creates a new file instance by hooking it up to an
  60 *                      anonymous inode, and a dentry that describe the "class"
  61 *                      of the file
  62 *
  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 * @flags:   [in]    flags
  67 *
  68 * Creates a new file by hooking it on a single inode. This is useful for files
  69 * that do not need to have a full-fledged inode in order to operate correctly.
  70 * All the files created with anon_inode_getfile() will share a single inode,
  71 * hence saving memory and avoiding code duplication for the file/inode/dentry
  72 * setup.  Returns the newly created file* or an error pointer.
  73 */
  74struct file *anon_inode_getfile(const char *name,
  75                                const struct file_operations *fops,
  76                                void *priv, int flags)
  77{
  78        struct file *file;
  79
  80        if (IS_ERR(anon_inode_inode))
  81                return ERR_PTR(-ENODEV);
  82
  83        if (fops->owner && !try_module_get(fops->owner))
  84                return ERR_PTR(-ENOENT);
  85
  86        /*
  87         * We know the anon_inode inode count is always greater than zero,
  88         * so ihold() is safe.
  89         */
  90        ihold(anon_inode_inode);
  91        file = alloc_file_pseudo(anon_inode_inode, anon_inode_mnt, name,
  92                                 flags & (O_ACCMODE | O_NONBLOCK), fops);
  93        if (IS_ERR(file))
  94                goto err;
  95
  96        file->f_mapping = anon_inode_inode->i_mapping;
  97
  98        file->private_data = priv;
  99
 100        return file;
 101
 102err:
 103        iput(anon_inode_inode);
 104        module_put(fops->owner);
 105        return file;
 106}
 107EXPORT_SYMBOL_GPL(anon_inode_getfile);
 108
 109/**
 110 * anon_inode_getfd - creates a new file instance by hooking it up to an
 111 *                    anonymous inode, and a dentry that describe the "class"
 112 *                    of the file
 113 *
 114 * @name:    [in]    name of the "class" of the new file
 115 * @fops:    [in]    file operations for the new file
 116 * @priv:    [in]    private data for the new file (will be file's private_data)
 117 * @flags:   [in]    flags
 118 *
 119 * Creates a new file by hooking it on a single inode. This is useful for files
 120 * that do not need to have a full-fledged inode in order to operate correctly.
 121 * All the files created with anon_inode_getfd() will share a single inode,
 122 * hence saving memory and avoiding code duplication for the file/inode/dentry
 123 * setup.  Returns new descriptor or an error code.
 124 */
 125int anon_inode_getfd(const char *name, const struct file_operations *fops,
 126                     void *priv, int flags)
 127{
 128        int error, fd;
 129        struct file *file;
 130
 131        error = get_unused_fd_flags(flags);
 132        if (error < 0)
 133                return error;
 134        fd = error;
 135
 136        file = anon_inode_getfile(name, fops, priv, flags);
 137        if (IS_ERR(file)) {
 138                error = PTR_ERR(file);
 139                goto err_put_unused_fd;
 140        }
 141        fd_install(fd, file);
 142
 143        return fd;
 144
 145err_put_unused_fd:
 146        put_unused_fd(fd);
 147        return error;
 148}
 149EXPORT_SYMBOL_GPL(anon_inode_getfd);
 150
 151static int __init anon_inode_init(void)
 152{
 153        anon_inode_mnt = kern_mount(&anon_inode_fs_type);
 154        if (IS_ERR(anon_inode_mnt))
 155                panic("anon_inode_init() kernel mount failed (%ld)\n", PTR_ERR(anon_inode_mnt));
 156
 157        anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
 158        if (IS_ERR(anon_inode_inode))
 159                panic("anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(anon_inode_inode));
 160
 161        return 0;
 162}
 163
 164fs_initcall(anon_inode_init);
 165
 166