fs/anon_inodes.c

   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
  26 static struct vfsmount *anon_inode_mnt __read_mostly;
  27 static struct inode *anon_inode_inode;
  28
  29 /*
  30  * anon_inodefs_dname() is called from d_path().
  31  */
  32 static 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
  38 static const struct dentry_operations anon_inodefs_dentry_operations = {
  39         .d_dname        = anon_inodefs_dname,
  40 };
  41
  42 static 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
  49 static 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  */
  71 struct 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
  99 err:
 100         iput(anon_inode_inode);
 101         module_put(fops->owner);
 102         return file;
 103 }
 104 EXPORT_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  */
 122 int 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
 142 err_put_unused_fd:
 143         put_unused_fd(fd);
 144         return error;
 145 }
 146 EXPORT_SYMBOL_GPL(anon_inode_getfd);
 147
 148 static 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
 161 fs_initcall(anon_inode_init);
 162