anon_inodes.c
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/*
* fs/anon_inodes.c
*
* Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
*
* Thanks to Arnd Bergmann for code review and suggestions.
* More changes for Thomas Gleixner suggestions.
*
*/
#include <linux/cred.h>
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/magic.h>
#include <linux/anon_inodes.h>
#include <asm/uaccess.h>
static struct vfsmount *anon_inode_mnt __read_mostly;
static struct inode *anon_inode_inode;
/*
* anon_inodefs_dname() is called from d_path().
*/
static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
{
return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
dentry->d_name.name);
}
static const struct dentry_operations anon_inodefs_dentry_operations = {
.d_dname = anon_inodefs_dname,
};
static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data)
{
struct dentry *root;
root = mount_pseudo(fs_type, "anon_inode:", NULL,
&anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC);
if (!IS_ERR(root)) {
struct super_block *s = root->d_sb;
anon_inode_inode = alloc_anon_inode(s);
if (IS_ERR(anon_inode_inode)) {
dput(root);
deactivate_locked_super(s);
root = ERR_CAST(anon_inode_inode);
}
}
return root;
}
static struct file_system_type anon_inode_fs_type = {
.name = "anon_inodefs",
.mount = anon_inodefs_mount,
.kill_sb = kill_anon_super,
};
/**
* anon_inode_getfile - creates a new file instance by hooking it up to an
* anonymous inode, and a dentry that describe the "class"
* of the file
*
* @name: [in] name of the "class" of the new file
* @fops: [in] file operations for the new file
* @priv: [in] private data for the new file (will be file's private_data)
* @flags: [in] flags
*
* Creates a new file by hooking it on a single inode. This is useful for files
* that do not need to have a full-fledged inode in order to operate correctly.
* All the files created with anon_inode_getfile() will share a single inode,
* hence saving memory and avoiding code duplication for the file/inode/dentry
* setup. Returns the newly created file* or an error pointer.
*/
struct file *anon_inode_getfile(const char *name,
const struct file_operations *fops,
void *priv, int flags)
{
struct qstr this;
struct path path;
struct file *file;
if (IS_ERR(anon_inode_inode))
return ERR_PTR(-ENODEV);
if (fops->owner && !try_module_get(fops->owner))
return ERR_PTR(-ENOENT);
/*
* Link the inode to a directory entry by creating a unique name
* using the inode sequence number.
*/
file = ERR_PTR(-ENOMEM);
this.name = name;
this.len = strlen(name);
this.hash = 0;
path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this);
if (!path.dentry)
goto err_module;
path.mnt = mntget(anon_inode_mnt);
/*
* We know the anon_inode inode count is always greater than zero,
* so ihold() is safe.
*/
ihold(anon_inode_inode);
d_instantiate(path.dentry, anon_inode_inode);
file = alloc_file(&path, OPEN_FMODE(flags), fops);
if (IS_ERR(file))
goto err_dput;
file->f_mapping = anon_inode_inode->i_mapping;
file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
file->private_data = priv;
return file;
err_dput:
path_put(&path);
err_module:
module_put(fops->owner);
return file;
}
EXPORT_SYMBOL_GPL(anon_inode_getfile);
/**
* anon_inode_getfd - creates a new file instance by hooking it up to an
* anonymous inode, and a dentry that describe the "class"
* of the file
*
* @name: [in] name of the "class" of the new file
* @fops: [in] file operations for the new file
* @priv: [in] private data for the new file (will be file's private_data)
* @flags: [in] flags
*
* Creates a new file by hooking it on a single inode. This is useful for files
* that do not need to have a full-fledged inode in order to operate correctly.
* All the files created with anon_inode_getfd() will share a single inode,
* hence saving memory and avoiding code duplication for the file/inode/dentry
* setup. Returns new descriptor or an error code.
*/
int anon_inode_getfd(const char *name, const struct file_operations *fops,
void *priv, int flags)
{
int error, fd;
struct file *file;
error = get_unused_fd_flags(flags);
if (error < 0)
return error;
fd = error;
file = anon_inode_getfile(name, fops, priv, flags);
if (IS_ERR(file)) {
error = PTR_ERR(file);
goto err_put_unused_fd;
}
fd_install(fd, file);
return fd;
err_put_unused_fd:
put_unused_fd(fd);
return error;
}
EXPORT_SYMBOL_GPL(anon_inode_getfd);
static int __init anon_inode_init(void)
{
int error;
error = register_filesystem(&anon_inode_fs_type);
if (error)
goto err_exit;
anon_inode_mnt = kern_mount(&anon_inode_fs_type);
if (IS_ERR(anon_inode_mnt)) {
error = PTR_ERR(anon_inode_mnt);
goto err_unregister_filesystem;
}
return 0;
err_unregister_filesystem:
unregister_filesystem(&anon_inode_fs_type);
err_exit:
panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
}
fs_initcall(anon_inode_init);