Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Fix error output of boot instance creation failure

   Currently if a boot instance creation fails, instead of printing out
   the name of the instance that failed, it prints "(null)". That is
   because it prints "cur_str" that had already been processed by
   strsep(). Print the saved name instead.

   While at it, print the error code of the failure.

 - Fix use-after-free for same named historgrams

   Histograms can be named so that they can be used in multiple events.
   But if the named histogram has a variable attached, the second event
   that uses the named histogram which duplicates it and needs to free
   the original after duplication leaves the old variable in place and
   still visible. If another histogram uses than variable, it will use
   the stale one which will try to reference the freed duplicate
   histogram and crash the kernel.

   Free the duplicate variables along with the duplicated histogram
   data.

 - Check return value of kthread_run() in event self test

   The events self tests uses a kthread for testing but does not check
   if it succeeded in creating a kthread. If the kthread creation were
   to fail, the code will still try to call kthread_stop() on the error
   returned.

 - Fix race between reading trace_pipe and updating subbuffer size

   If a user is reading the trace_pipe file at the same time they update
   the ring buffer sub-buffer size, can cause the trace_pipe read to
   read stale data. Add trace_access_lock() around updating the ring
   buffer sub-buffer size.

 - Fix eventfs_inode on failure path in creation of the events directory

   In the creation of the "events" directory, if after allocating the
   eventfs_inode a failure is detected, it calls cleanup_ei() which
   calls free_ei(). The free_ei() will test if eventfs_inode being freed
   has no children. It is a bug if it does. But on the failure case of
   the creation of the "events" directory, the children lists have not
   yet been initialized and the free will trigger a warning because
   list_empty() on an uninitialized list returns false.

   Move the initialization into init_ei() where it makes more sense and
   makes sure that a created eventfs_inode has its lists initialized
   upon creation.

 - Check return value of kthread_run() in ftrace direct sample code

   The sample code that shows how to use the ftrace direct calls does
   not test the return of kthread_run() to see if it succeeds. Return a
   failure if the kthread_run() doesn't succeed.

 - Clear user events state on fork in case of alloc failure

   On fork, the child gets a pointer to the parent's user events state.
   It makes a copy of it then updates the child's pointer to it. But if
   the allocation fails, the duplication function leaves the child with
   a pointer to its parent's descriptor. When the child cleans up its
   data, it will free the parent's descriptor while the parent is still
   using it.

   In the duplication function, set the child's user_event_mm to NULL
   before testing if the allocation succeeded, and when it exits it will
   not free the parent's descriptor.

 - Fix retry exhaustion in simple ring buffer reader swap

   simple_ring_buffer_swap_reader_page() starts with retry set to 8 and
   post-decrements it only after a failed link replacement. On the final
   attempt, a successful replacement leaves retry at zero, while a
   failed replacement leaves it at -1.

   But the check for success expects the retry value to be non-zero and
   exits with an error on zero. This is the opposite result. Fix it.

 - Fail nicely when the remote swap_reader_page() returns an error

   Currently, if the swap_reader_page() of a remote buffer fails, it
   triggers a WARN_ON_ONCE() and continues normally. Instead, have it
   exit with an error and a pr_warn() print instead of a full WARNING.

* tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Stop remote reader update when page swap fails
  tracing: Fix retry exhaustion in simple ring buffer reader swap
  tracing/user_events: Clear copied tracing state before fork duplication
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify
  eventfs: Initialize ei->children and ei->list in init_ei()
  tracing: Fix use-after-free in trace_pipe read on sub-buffer order change
  tracing: Fix crash passing ERR_PTR to kthread_stop()
  tracing: Fix use-after-free with same-name named triggers
  tracing: Fix logged instance name on creation failure

5 files changed, 1631 insertions, 0 deletions

diff --git a/fs/hostfs/Makefile b/fs/hostfs/Makefile
new file mode 100644
index 000000000..16be592e8
--- /dev/null
+++ b/fs/hostfs/Makefile
@@ -0,0 +1,13 @@
+#
+# Copyright (C) 2000 Jeff Dike (jdike@karaya.com)
+# Licensed under the GPL
+#
+
+hostfs-objs := hostfs_kern.o
+
+hostfs-builtin-$(CONFIG_HOSTFS) += hostfs_user.o hostfs_user_exp.o
+
+obj-y := $(hostfs-builtin-y) $(hostfs-builtin-m)
+obj-$(CONFIG_HOSTFS) += hostfs.o
+
+include $(srctree)/arch/um/scripts/Makefile.rules
diff --git a/fs/hostfs/hostfs.h b/fs/hostfs/hostfs.h
new file mode 100644
index 000000000..aa02599b7
--- /dev/null
+++ b/fs/hostfs/hostfs.h
@@ -0,0 +1,73 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UM_FS_HOSTFS
+#define __UM_FS_HOSTFS
+
+#include <os.h>
+#include <generated/asm-offsets.h>
+
+struct hostfs_timespec {
+	long long tv_sec;
+	long long tv_nsec;
+};
+
+struct hostfs_iattr {
+	unsigned int		ia_valid;
+	unsigned short		ia_mode;
+	uid_t			ia_uid;
+	gid_t			ia_gid;
+	loff_t			ia_size;
+	struct hostfs_timespec	ia_atime;
+	struct hostfs_timespec	ia_mtime;
+	struct hostfs_timespec	ia_ctime;
+};
+
+struct hostfs_stat {
+	unsigned long long ino;
+	unsigned int mode;
+	unsigned int nlink;
+	unsigned int uid;
+	unsigned int gid;
+	unsigned long long size;
+	struct hostfs_timespec atime, mtime, ctime, btime;
+	unsigned int blksize;
+	unsigned long long blocks;
+	struct {
+		unsigned int maj;
+		unsigned int min;
+	} rdev, dev;
+};
+
+extern int stat_file(const char *path, struct hostfs_stat *p, int fd);
+extern int access_file(char *path, int r, int w, int x);
+extern int open_file(char *path, int r, int w, int append);
+extern void *open_dir(char *path, int *err_out);
+extern void seek_dir(void *stream, unsigned long long pos);
+extern char *read_dir(void *stream, unsigned long long *pos_out,
+		      unsigned long long *ino_out, int *len_out,
+		      unsigned int *type_out);
+extern void close_file(void *stream);
+extern int replace_file(int oldfd, int fd);
+extern void close_dir(void *stream);
+extern int read_file(int fd, unsigned long long *offset, char *buf, int len);
+extern int write_file(int fd, unsigned long long *offset, const char *buf,
+		      int len);
+extern int lseek_file(int fd, long long offset, int whence);
+extern int fsync_file(int fd, int datasync);
+extern int file_create(char *name, int mode);
+extern int set_attr(const char *file, struct hostfs_iattr *attrs, int fd);
+extern int make_symlink(const char *from, const char *to);
+extern int unlink_file(const char *file);
+extern int do_mkdir(const char *file, int mode);
+extern int hostfs_do_rmdir(const char *file);
+extern int do_mknod(const char *file, int mode, unsigned int major,
+		    unsigned int minor);
+extern int link_file(const char *to, const char *from);
+extern int hostfs_do_readlink(char *file, char *buf, int size);
+extern int rename_file(char *from, char *to);
+extern int rename2_file(char *from, char *to, unsigned int flags);
+extern int do_statfs(char *root, long *bsize_out, long long *blocks_out,
+		     long long *bfree_out, long long *bavail_out,
+		     long long *files_out, long long *ffree_out,
+		     void *fsid_out, int fsid_size, long *namelen_out);
+
+#endif
diff --git a/fs/hostfs/hostfs_kern.c b/fs/hostfs/hostfs_kern.c
new file mode 100644
index 000000000..7add056d4
--- /dev/null
+++ b/fs/hostfs/hostfs_kern.c
@@ -0,0 +1,1096 @@
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ * Licensed under the GPL
+ *
+ * Ported the filesystem routines to 2.5.
+ * 2003-02-10 Petr Baudis <pasky@ucw.cz>
+ */
+
+#include <linux/fs.h>
+#include <linux/magic.h>
+#include <linux/module.h>
+#include <linux/mm.h>
+#include <linux/pagemap.h>
+#include <linux/statfs.h>
+#include <linux/slab.h>
+#include <linux/seq_file.h>
+#include <linux/writeback.h>
+#include <linux/mount.h>
+#include <linux/fs_context.h>
+#include <linux/fs_parser.h>
+#include <linux/namei.h>
+#include "hostfs.h"
+#include <init.h>
+#include <kern.h>
+
+struct hostfs_fs_info {
+	char *host_root_path;
+};
+
+struct hostfs_inode_info {
+	int fd;
+	fmode_t mode;
+	struct inode vfs_inode;
+	struct mutex open_mutex;
+	dev_t dev;
+	struct hostfs_timespec btime;
+};
+
+static inline struct hostfs_inode_info *HOSTFS_I(struct inode *inode)
+{
+	return list_entry(inode, struct hostfs_inode_info, vfs_inode);
+}
+
+#define FILE_HOSTFS_I(file) HOSTFS_I(file_inode(file))
+
+static struct kmem_cache *hostfs_inode_cache;
+
+/* Changed in hostfs_args before the kernel starts running */
+static char *root_ino = "";
+static int append = 0;
+
+static const struct inode_operations hostfs_iops;
+static const struct inode_operations hostfs_dir_iops;
+static const struct inode_operations hostfs_link_iops;
+
+#ifndef MODULE
+static int __init hostfs_args(char *options, int *add)
+{
+	char *ptr;
+
+	*add = 0;
+	ptr = strchr(options, ',');
+	if (ptr != NULL)
+		*ptr++ = '\0';
+	if (*options != '\0')
+		root_ino = options;
+
+	options = ptr;
+	while (options) {
+		ptr = strchr(options, ',');
+		if (ptr != NULL)
+			*ptr++ = '\0';
+		if (*options != '\0') {
+			if (!strcmp(options, "append"))
+				append = 1;
+			else printf("hostfs_args - unsupported option - %s\n",
+				    options);
+		}
+		options = ptr;
+	}
+	return 0;
+}
+
+__uml_setup("hostfs=", hostfs_args,
+"hostfs=<root dir>,<flags>,...\n"
+"    This is used to set hostfs parameters.  The root directory argument\n"
+"    is used to confine all hostfs mounts to within the specified directory\n"
+"    tree on the host.  If this isn't specified, then a user inside UML can\n"
+"    mount anything on the host that's accessible to the user that's running\n"
+"    it.\n"
+"    The only flag currently supported is 'append', which specifies that all\n"
+"    files opened by hostfs will be opened in append mode.\n\n"
+);
+#endif
+
+static char *__dentry_name(struct dentry *dentry, char *name)
+{
+	char *p = dentry_path_raw(dentry, name, PATH_MAX);
+	struct hostfs_fs_info *fsi = dentry->d_sb->s_fs_info;
+	char *root = fsi->host_root_path;
+	size_t len = strlen(root);
+
+	if (IS_ERR(p) || len > p - name) {
+		__putname(name);
+		return NULL;
+	}
+
+	memcpy(name, root, len);
+	memmove(name + len, p, name + PATH_MAX - p);
+
+	return name;
+}
+
+static char *dentry_name(struct dentry *dentry)
+{
+	char *name = __getname();
+	if (!name)
+		return NULL;
+
+	return __dentry_name(dentry, name);
+}
+
+static char *inode_name(struct inode *ino)
+{
+	struct dentry *dentry;
+	char *name;
+
+	dentry = d_find_alias(ino);
+	if (!dentry)
+		return NULL;
+
+	name = dentry_name(dentry);
+
+	dput(dentry);
+
+	return name;
+}
+
+static char *follow_link(char *link)
+{
+	char *name, *resolved, *end;
+	int n;
+
+	name = kmalloc(PATH_MAX, GFP_KERNEL);
+	if (!name) {
+		n = -ENOMEM;
+		goto out_free;
+	}
+
+	n = hostfs_do_readlink(link, name, PATH_MAX);
+	if (n < 0)
+		goto out_free;
+	else if (n == PATH_MAX) {
+		n = -E2BIG;
+		goto out_free;
+	}
+
+	if (*name == '/')
+		return name;
+
+	end = strrchr(link, '/');
+	if (end == NULL)
+		return name;
+
+	*(end + 1) = '\0';
+
+	resolved = kasprintf(GFP_KERNEL, "%s%s", link, name);
+	if (resolved == NULL) {
+		n = -ENOMEM;
+		goto out_free;
+	}
+
+	kfree(name);
+	return resolved;
+
+ out_free:
+	kfree(name);
+	return ERR_PTR(n);
+}
+
+static int hostfs_statfs(struct dentry *dentry, struct kstatfs *sf)
+{
+	/*
+	 * do_statfs uses struct statfs64 internally, but the linux kernel
+	 * struct statfs still has 32-bit versions for most of these fields,
+	 * so we convert them here
+	 */
+	int err;
+	long long f_blocks;
+	long long f_bfree;
+	long long f_bavail;
+	long long f_files;
+	long long f_ffree;
+	struct hostfs_fs_info *fsi;
+
+	fsi = dentry->d_sb->s_fs_info;
+	err = do_statfs(fsi->host_root_path,
+			&sf->f_bsize, &f_blocks, &f_bfree, &f_bavail, &f_files,
+			&f_ffree, &sf->f_fsid, sizeof(sf->f_fsid),
+			&sf->f_namelen);
+	if (err)
+		return err;
+	sf->f_blocks = f_blocks;
+	sf->f_bfree = f_bfree;
+	sf->f_bavail = f_bavail;
+	sf->f_files = f_files;
+	sf->f_ffree = f_ffree;
+	sf->f_type = HOSTFS_SUPER_MAGIC;
+	return 0;
+}
+
+static struct inode *hostfs_alloc_inode(struct super_block *sb)
+{
+	struct hostfs_inode_info *hi;
+
+	hi = alloc_inode_sb(sb, hostfs_inode_cache, GFP_KERNEL_ACCOUNT);
+	if (hi == NULL)
+		return NULL;
+	hi->fd = -1;
+	hi->mode = 0;
+	hi->dev = 0;
+	inode_init_once(&hi->vfs_inode);
+	mutex_init(&hi->open_mutex);
+	return &hi->vfs_inode;
+}
+
+static void hostfs_evict_inode(struct inode *inode)
+{
+	truncate_inode_pages_final(&inode->i_data);
+	clear_inode(inode);
+	if (HOSTFS_I(inode)->fd != -1) {
+		close_file(&HOSTFS_I(inode)->fd);
+		HOSTFS_I(inode)->fd = -1;
+		HOSTFS_I(inode)->dev = 0;
+	}
+}
+
+static void hostfs_free_inode(struct inode *inode)
+{
+	kmem_cache_free(hostfs_inode_cache, HOSTFS_I(inode));
+}
+
+static int hostfs_show_options(struct seq_file *seq, struct dentry *root)
+{
+	struct hostfs_fs_info *fsi;
+	const char *root_path;
+
+	fsi = root->d_sb->s_fs_info;
+	root_path = fsi->host_root_path;
+	size_t offset = strlen(root_ino) + 1;
+
+	if (strlen(root_path) > offset)
+		seq_show_option(seq, root_path + offset, NULL);
+
+	if (append)
+		seq_puts(seq, ",append");
+
+	return 0;
+}
+
+static const struct super_operations hostfs_sbops = {
+	.alloc_inode	= hostfs_alloc_inode,
+	.free_inode	= hostfs_free_inode,
+	.drop_inode	= inode_just_drop,
+	.evict_inode	= hostfs_evict_inode,
+	.statfs		= hostfs_statfs,
+	.show_options	= hostfs_show_options,
+};
+
+static int hostfs_readdir(struct file *file, struct dir_context *ctx)
+{
+	void *dir;
+	char *name;
+	unsigned long long next, ino;
+	int error, len;
+	unsigned int type;
+
+	name = dentry_name(file->f_path.dentry);
+	if (name == NULL)
+		return -ENOMEM;
+	dir = open_dir(name, &error);
+	__putname(name);
+	if (dir == NULL)
+		return -error;
+	next = ctx->pos;
+	seek_dir(dir, next);
+	while ((name = read_dir(dir, &next, &ino, &len, &type)) != NULL) {
+		if (!dir_emit(ctx, name, len, ino, type))
+			break;
+		ctx->pos = next;
+	}
+	close_dir(dir);
+	return 0;
+}
+
+static int hostfs_open(struct inode *ino, struct file *file)
+{
+	char *name;
+	fmode_t mode;
+	int err;
+	int r, w, fd;
+
+	mode = file->f_mode & (FMODE_READ | FMODE_WRITE);
+	if ((mode & HOSTFS_I(ino)->mode) == mode)
+		return 0;
+
+	mode |= HOSTFS_I(ino)->mode;
+
+retry:
+	r = w = 0;
+
+	if (mode & FMODE_READ)
+		r = 1;
+	if (mode & FMODE_WRITE)
+		r = w = 1;
+
+	name = dentry_name(file_dentry(file));
+	if (name == NULL)
+		return -ENOMEM;
+
+	fd = open_file(name, r, w, append);
+	__putname(name);
+	if (fd < 0)
+		return fd;
+
+	mutex_lock(&HOSTFS_I(ino)->open_mutex);
+	/* somebody else had handled it first? */
+	if ((mode & HOSTFS_I(ino)->mode) == mode) {
+		mutex_unlock(&HOSTFS_I(ino)->open_mutex);
+		close_file(&fd);
+		return 0;
+	}
+	if ((mode | HOSTFS_I(ino)->mode) != mode) {
+		mode |= HOSTFS_I(ino)->mode;
+		mutex_unlock(&HOSTFS_I(ino)->open_mutex);
+		close_file(&fd);
+		goto retry;
+	}
+	if (HOSTFS_I(ino)->fd == -1) {
+		HOSTFS_I(ino)->fd = fd;
+	} else {
+		err = replace_file(fd, HOSTFS_I(ino)->fd);
+		close_file(&fd);
+		if (err < 0) {
+			mutex_unlock(&HOSTFS_I(ino)->open_mutex);
+			return err;
+		}
+	}
+	HOSTFS_I(ino)->mode = mode;
+	mutex_unlock(&HOSTFS_I(ino)->open_mutex);
+
+	return 0;
+}
+
+static int hostfs_file_release(struct inode *inode, struct file *file)
+{
+	filemap_write_and_wait(inode->i_mapping);
+
+	return 0;
+}
+
+static int hostfs_fsync(struct file *file, loff_t start, loff_t end,
+			int datasync)
+{
+	struct inode *inode = file->f_mapping->host;
+	int ret;
+
+	ret = file_write_and_wait_range(file, start, end);
+	if (ret)
+		return ret;
+
+	inode_lock(inode);
+	ret = fsync_file(HOSTFS_I(inode)->fd, datasync);
+	inode_unlock(inode);
+
+	return ret;
+}
+
+static const struct file_operations hostfs_file_fops = {
+	.llseek		= generic_file_llseek,
+	.splice_read	= filemap_splice_read,
+	.splice_write	= iter_file_splice_write,
+	.read_iter	= generic_file_read_iter,
+	.write_iter	= generic_file_write_iter,
+	.mmap_prepare	= generic_file_mmap_prepare,
+	.open		= hostfs_open,
+	.release	= hostfs_file_release,
+	.fsync		= hostfs_fsync,
+};
+
+static const struct file_operations hostfs_dir_fops = {
+	.llseek		= generic_file_llseek,
+	.iterate_shared	= hostfs_readdir,
+	.read		= generic_read_dir,
+	.open		= hostfs_open,
+	.fsync		= hostfs_fsync,
+};
+
+static int hostfs_writepages(struct address_space *mapping,
+		struct writeback_control *wbc)
+{
+	struct inode *inode = mapping->host;
+	struct folio *folio = NULL;
+	loff_t i_size = i_size_read(inode);
+	int err = 0;
+
+	while ((folio = writeback_iter(mapping, wbc, folio, &err))) {
+		loff_t pos = folio_pos(folio);
+		size_t count = folio_size(folio);
+		char *buffer;
+		int ret;
+
+		if (count > i_size - pos)
+			count = i_size - pos;
+
+		buffer = kmap_local_folio(folio, 0);
+		ret = write_file(HOSTFS_I(inode)->fd, &pos, buffer, count);
+		kunmap_local(buffer);
+		folio_unlock(folio);
+		if (ret != count) {
+			err = ret < 0 ? ret : -EIO;
+			mapping_set_error(mapping, err);
+		}
+	}
+
+	return err;
+}
+
+static int hostfs_read_folio(struct file *file, struct folio *folio)
+{
+	char *buffer;
+	loff_t start = folio_pos(folio);
+	int bytes_read, ret = 0;
+
+	buffer = kmap_local_folio(folio, 0);
+	bytes_read = read_file(FILE_HOSTFS_I(file)->fd, &start, buffer,
+			PAGE_SIZE);
+	if (bytes_read < 0)
+		ret = bytes_read;
+	else
+		buffer = folio_zero_tail(folio, bytes_read, buffer + bytes_read);
+	kunmap_local(buffer);
+
+	folio_end_read(folio, ret == 0);
+	return ret;
+}
+
+static int hostfs_write_begin(const struct kiocb *iocb,
+			      struct address_space *mapping,
+			      loff_t pos, unsigned len,
+			      struct folio **foliop, void **fsdata)
+{
+	pgoff_t index = pos >> PAGE_SHIFT;
+
+	*foliop = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
+			mapping_gfp_mask(mapping));
+	if (IS_ERR(*foliop))
+		return PTR_ERR(*foliop);
+	return 0;
+}
+
+static int hostfs_write_end(const struct kiocb *iocb,
+			    struct address_space *mapping,
+			    loff_t pos, unsigned len, unsigned copied,
+			    struct folio *folio, void *fsdata)
+{
+	struct inode *inode = mapping->host;
+	void *buffer;
+	size_t from = offset_in_folio(folio, pos);
+	int err;
+
+	buffer = kmap_local_folio(folio, from);
+	err = write_file(FILE_HOSTFS_I(iocb->ki_filp)->fd, &pos, buffer, copied);
+	kunmap_local(buffer);
+
+	if (!folio_test_uptodate(folio) && err == folio_size(folio))
+		folio_mark_uptodate(folio);
+
+	/*
+	 * If err > 0, write_file has added err to pos, so we are comparing
+	 * i_size against the last byte written.
+	 */
+	if (err > 0 && (pos > inode->i_size))
+		inode->i_size = pos;
+	folio_unlock(folio);
+	folio_put(folio);
+
+	return err;
+}
+
+static const struct address_space_operations hostfs_aops = {
+	.writepages 	= hostfs_writepages,
+	.read_folio	= hostfs_read_folio,
+	.dirty_folio	= filemap_dirty_folio,
+	.write_begin	= hostfs_write_begin,
+	.write_end	= hostfs_write_end,
+	.migrate_folio	= filemap_migrate_folio,
+};
+
+static int hostfs_inode_update(struct inode *ino, const struct hostfs_stat *st)
+{
+	set_nlink(ino, st->nlink);
+	i_uid_write(ino, st->uid);
+	i_gid_write(ino, st->gid);
+	inode_set_atime_to_ts(ino, (struct timespec64){
+			st->atime.tv_sec,
+			st->atime.tv_nsec,
+		});
+	inode_set_mtime_to_ts(ino, (struct timespec64){
+			st->mtime.tv_sec,
+			st->mtime.tv_nsec,
+		});
+	inode_set_ctime(ino, st->ctime.tv_sec, st->ctime.tv_nsec);
+	ino->i_size = st->size;
+	ino->i_blocks = st->blocks;
+	return 0;
+}
+
+static int hostfs_inode_set(struct inode *ino, void *data)
+{
+	struct hostfs_stat *st = data;
+	dev_t dev, rdev;
+
+	/* Reencode maj and min with the kernel encoding.*/
+	rdev = MKDEV(st->rdev.maj, st->rdev.min);
+	dev = MKDEV(st->dev.maj, st->dev.min);
+
+	switch (st->mode & S_IFMT) {
+	case S_IFLNK:
+		ino->i_op = &hostfs_link_iops;
+		break;
+	case S_IFDIR:
+		ino->i_op = &hostfs_dir_iops;
+		ino->i_fop = &hostfs_dir_fops;
+		break;
+	case S_IFCHR:
+	case S_IFBLK:
+	case S_IFIFO:
+	case S_IFSOCK:
+		init_special_inode(ino, st->mode & S_IFMT, rdev);
+		ino->i_op = &hostfs_iops;
+		break;
+	case S_IFREG:
+		ino->i_op = &hostfs_iops;
+		ino->i_fop = &hostfs_file_fops;
+		ino->i_mapping->a_ops = &hostfs_aops;
+		break;
+	default:
+		return -EIO;
+	}
+
+	HOSTFS_I(ino)->dev = dev;
+	HOSTFS_I(ino)->btime = st->btime;
+	ino->i_ino = st->ino;
+	ino->i_mode = st->mode;
+	return hostfs_inode_update(ino, st);
+}
+
+static int hostfs_inode_test(struct inode *inode, void *data)
+{
+	const struct hostfs_stat *st = data;
+	dev_t dev = MKDEV(st->dev.maj, st->dev.min);
+
+	return inode->i_ino == st->ino && HOSTFS_I(inode)->dev == dev &&
+	       (inode->i_mode & S_IFMT) == (st->mode & S_IFMT) &&
+	       HOSTFS_I(inode)->btime.tv_sec == st->btime.tv_sec &&
+	       HOSTFS_I(inode)->btime.tv_nsec == st->btime.tv_nsec;
+}
+
+static struct inode *hostfs_iget(struct super_block *sb, char *name)
+{
+	struct inode *inode;
+	struct hostfs_stat st;
+	int err = stat_file(name, &st, -1);
+
+	if (err)
+		return ERR_PTR(err);
+
+	inode = iget5_locked(sb, st.ino, hostfs_inode_test, hostfs_inode_set,
+			     &st);
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+
+	if (inode_state_read_once(inode) & I_NEW) {
+		unlock_new_inode(inode);
+	} else {
+		spin_lock(&inode->i_lock);
+		hostfs_inode_update(inode, &st);
+		spin_unlock(&inode->i_lock);
+	}
+
+	return inode;
+}
+
+static int hostfs_create(struct mnt_idmap *idmap, struct inode *dir,
+			 struct dentry *dentry, umode_t mode)
+{
+	struct inode *inode;
+	char *name;
+	int fd;
+
+	name = dentry_name(dentry);
+	if (name == NULL)
+		return -ENOMEM;
+
+	fd = file_create(name, mode & 0777);
+	if (fd < 0) {
+		__putname(name);
+		return fd;
+	}
+
+	inode = hostfs_iget(dir->i_sb, name);
+	__putname(name);
+	if (IS_ERR(inode))
+		return PTR_ERR(inode);
+
+	HOSTFS_I(inode)->fd = fd;
+	HOSTFS_I(inode)->mode = FMODE_READ | FMODE_WRITE;
+	d_instantiate(dentry, inode);
+	return 0;
+}
+
+static struct dentry *hostfs_lookup(struct inode *ino, struct dentry *dentry,
+				    unsigned int flags)
+{
+	struct inode *inode = NULL;
+	char *name;
+
+	name = dentry_name(dentry);
+	if (name == NULL)
+		return ERR_PTR(-ENOMEM);
+
+	inode = hostfs_iget(ino->i_sb, name);
+	__putname(name);
+	if (inode == ERR_PTR(-ENOENT))
+		inode = NULL;
+
+	return d_splice_alias(inode, dentry);
+}
+
+static int hostfs_link(struct dentry *to, struct inode *ino,
+		       struct dentry *from)
+{
+	char *from_name, *to_name;
+	int err;
+
+	if ((from_name = dentry_name(from)) == NULL)
+		return -ENOMEM;
+	to_name = dentry_name(to);
+	if (to_name == NULL) {
+		__putname(from_name);
+		return -ENOMEM;
+	}
+	err = link_file(to_name, from_name);
+	__putname(from_name);
+	__putname(to_name);
+	return err;
+}
+
+static int hostfs_unlink(struct inode *ino, struct dentry *dentry)
+{
+	char *file;
+	int err;
+
+	if (append)
+		return -EPERM;
+
+	if ((file = dentry_name(dentry)) == NULL)
+		return -ENOMEM;
+
+	err = unlink_file(file);
+	__putname(file);
+	return err;
+}
+
+static int hostfs_symlink(struct mnt_idmap *idmap, struct inode *ino,
+			  struct dentry *dentry, const char *to)
+{
+	char *file;
+	int err;
+
+	if ((file = dentry_name(dentry)) == NULL)
+		return -ENOMEM;
+	err = make_symlink(file, to);
+	__putname(file);
+	return err;
+}
+
+static struct dentry *hostfs_mkdir(struct mnt_idmap *idmap, struct inode *ino,
+				   struct dentry *dentry, umode_t mode)
+{
+	struct inode *inode;
+	char *file;
+	int err;
+
+	if ((file = dentry_name(dentry)) == NULL)
+		return ERR_PTR(-ENOMEM);
+	err = do_mkdir(file, mode);
+	if (err) {
+		dentry = ERR_PTR(err);
+	} else {
+		inode = hostfs_iget(dentry->d_sb, file);
+		d_drop(dentry);
+		dentry = d_splice_alias(inode, dentry);
+	}
+	__putname(file);
+	return dentry;
+}
+
+static int hostfs_rmdir(struct inode *ino, struct dentry *dentry)
+{
+	char *file;
+	int err;
+
+	if ((file = dentry_name(dentry)) == NULL)
+		return -ENOMEM;
+	err = hostfs_do_rmdir(file);
+	__putname(file);
+	return err;
+}
+
+static int hostfs_mknod(struct mnt_idmap *idmap, struct inode *dir,
+			struct dentry *dentry, umode_t mode, dev_t dev)
+{
+	struct inode *inode;
+	char *name;
+	int err;
+
+	name = dentry_name(dentry);
+	if (name == NULL)
+		return -ENOMEM;
+
+	err = do_mknod(name, mode, MAJOR(dev), MINOR(dev));
+	if (err) {
+		__putname(name);
+		return err;
+	}
+
+	inode = hostfs_iget(dir->i_sb, name);
+	__putname(name);
+	if (IS_ERR(inode))
+		return PTR_ERR(inode);
+
+	d_instantiate(dentry, inode);
+	return 0;
+}
+
+static int hostfs_rename2(struct mnt_idmap *idmap,
+			  struct inode *old_dir, struct dentry *old_dentry,
+			  struct inode *new_dir, struct dentry *new_dentry,
+			  unsigned int flags)
+{
+	char *old_name, *new_name;
+	int err;
+
+	if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
+		return -EINVAL;
+
+	old_name = dentry_name(old_dentry);
+	if (old_name == NULL)
+		return -ENOMEM;
+	new_name = dentry_name(new_dentry);
+	if (new_name == NULL) {
+		__putname(old_name);
+		return -ENOMEM;
+	}
+	if (!flags)
+		err = rename_file(old_name, new_name);
+	else
+		err = rename2_file(old_name, new_name, flags);
+
+	__putname(old_name);
+	__putname(new_name);
+	return err;
+}
+
+static int hostfs_permission(struct mnt_idmap *idmap,
+			     struct inode *ino, int desired)
+{
+	char *name;
+	int r = 0, w = 0, x = 0, err;
+
+	if (desired & MAY_NOT_BLOCK)
+		return -ECHILD;
+
+	if (desired & MAY_READ) r = 1;
+	if (desired & MAY_WRITE) w = 1;
+	if (desired & MAY_EXEC) x = 1;
+	name = inode_name(ino);
+	if (name == NULL)
+		return -ENOMEM;
+
+	if (S_ISCHR(ino->i_mode) || S_ISBLK(ino->i_mode) ||
+	    S_ISFIFO(ino->i_mode) || S_ISSOCK(ino->i_mode))
+		err = 0;
+	else
+		err = access_file(name, r, w, x);
+	__putname(name);
+	if (!err)
+		err = generic_permission(&nop_mnt_idmap, ino, desired);
+	return err;
+}
+
+static int hostfs_setattr(struct mnt_idmap *idmap,
+			  struct dentry *dentry, struct iattr *attr)
+{
+	struct inode *inode = d_inode(dentry);
+	struct hostfs_iattr attrs;
+	char *name;
+	int err;
+
+	int fd = HOSTFS_I(inode)->fd;
+
+	err = setattr_prepare(&nop_mnt_idmap, dentry, attr);
+	if (err)
+		return err;
+
+	if (append)
+		attr->ia_valid &= ~ATTR_SIZE;
+
+	attrs.ia_valid = 0;
+	if (attr->ia_valid & ATTR_MODE) {
+		attrs.ia_valid |= HOSTFS_ATTR_MODE;
+		attrs.ia_mode = attr->ia_mode;
+	}
+	if (attr->ia_valid & ATTR_UID) {
+		attrs.ia_valid |= HOSTFS_ATTR_UID;
+		attrs.ia_uid = from_kuid(&init_user_ns, attr->ia_uid);
+	}
+	if (attr->ia_valid & ATTR_GID) {
+		attrs.ia_valid |= HOSTFS_ATTR_GID;
+		attrs.ia_gid = from_kgid(&init_user_ns, attr->ia_gid);
+	}
+	if (attr->ia_valid & ATTR_SIZE) {
+		attrs.ia_valid |= HOSTFS_ATTR_SIZE;
+		attrs.ia_size = attr->ia_size;
+	}
+	if (attr->ia_valid & ATTR_ATIME) {
+		attrs.ia_valid |= HOSTFS_ATTR_ATIME;
+		attrs.ia_atime = (struct hostfs_timespec)
+			{ attr->ia_atime.tv_sec, attr->ia_atime.tv_nsec };
+	}
+	if (attr->ia_valid & ATTR_MTIME) {
+		attrs.ia_valid |= HOSTFS_ATTR_MTIME;
+		attrs.ia_mtime = (struct hostfs_timespec)
+			{ attr->ia_mtime.tv_sec, attr->ia_mtime.tv_nsec };
+	}
+	if (attr->ia_valid & ATTR_CTIME) {
+		attrs.ia_valid |= HOSTFS_ATTR_CTIME;
+		attrs.ia_ctime = (struct hostfs_timespec)
+			{ attr->ia_ctime.tv_sec, attr->ia_ctime.tv_nsec };
+	}
+	if (attr->ia_valid & ATTR_ATIME_SET) {
+		attrs.ia_valid |= HOSTFS_ATTR_ATIME_SET;
+	}
+	if (attr->ia_valid & ATTR_MTIME_SET) {
+		attrs.ia_valid |= HOSTFS_ATTR_MTIME_SET;
+	}
+	name = dentry_name(dentry);
+	if (name == NULL)
+		return -ENOMEM;
+	err = set_attr(name, &attrs, fd);
+	__putname(name);
+	if (err)
+		return err;
+
+	if ((attr->ia_valid & ATTR_SIZE) &&
+	    attr->ia_size != i_size_read(inode))
+		truncate_setsize(inode, attr->ia_size);
+
+	setattr_copy(&nop_mnt_idmap, inode, attr);
+	mark_inode_dirty(inode);
+	return 0;
+}
+
+static const struct inode_operations hostfs_iops = {
+	.permission	= hostfs_permission,
+	.setattr	= hostfs_setattr,
+};
+
+static const struct inode_operations hostfs_dir_iops = {
+	.create		= hostfs_create,
+	.lookup		= hostfs_lookup,
+	.link		= hostfs_link,
+	.unlink		= hostfs_unlink,
+	.symlink	= hostfs_symlink,
+	.mkdir		= hostfs_mkdir,
+	.rmdir		= hostfs_rmdir,
+	.mknod		= hostfs_mknod,
+	.rename		= hostfs_rename2,
+	.permission	= hostfs_permission,
+	.setattr	= hostfs_setattr,
+};
+
+static const char *hostfs_get_link(struct dentry *dentry,
+				   struct inode *inode,
+				   struct delayed_call *done)
+{
+	char *link;
+	if (!dentry)
+		return ERR_PTR(-ECHILD);
+	link = kmalloc(PATH_MAX, GFP_KERNEL);
+	if (link) {
+		char *path = dentry_name(dentry);
+		int err = -ENOMEM;
+		if (path) {
+			err = hostfs_do_readlink(path, link, PATH_MAX);
+			if (err == PATH_MAX)
+				err = -E2BIG;
+			__putname(path);
+		}
+		if (err < 0) {
+			kfree(link);
+			return ERR_PTR(err);
+		}
+	} else {
+		return ERR_PTR(-ENOMEM);
+	}
+
+	set_delayed_call(done, kfree_link, link);
+	return link;
+}
+
+static const struct inode_operations hostfs_link_iops = {
+	.get_link	= hostfs_get_link,
+};
+
+static int hostfs_fill_super(struct super_block *sb, struct fs_context *fc)
+{
+	struct hostfs_fs_info *fsi = sb->s_fs_info;
+	struct inode *root_inode;
+	int err;
+
+	sb->s_blocksize = 1024;
+	sb->s_blocksize_bits = 10;
+	sb->s_magic = HOSTFS_SUPER_MAGIC;
+	sb->s_op = &hostfs_sbops;
+	sb->s_d_flags = DCACHE_DONTCACHE;
+	sb->s_maxbytes = MAX_LFS_FILESIZE;
+	err = super_setup_bdi(sb);
+	if (err)
+		return err;
+
+	root_inode = hostfs_iget(sb, fsi->host_root_path);
+	if (IS_ERR(root_inode))
+		return PTR_ERR(root_inode);
+
+	if (S_ISLNK(root_inode->i_mode)) {
+		char *name;
+
+		iput(root_inode);
+		name = follow_link(fsi->host_root_path);
+		if (IS_ERR(name))
+			return PTR_ERR(name);
+
+		root_inode = hostfs_iget(sb, name);
+		kfree(name);
+		if (IS_ERR(root_inode))
+			return PTR_ERR(root_inode);
+	}
+
+	sb->s_root = d_make_root(root_inode);
+	if (sb->s_root == NULL)
+		return -ENOMEM;
+
+	return 0;
+}
+
+enum hostfs_parma {
+	Opt_hostfs,
+};
+
+static const struct fs_parameter_spec hostfs_param_specs[] = {
+	fsparam_string_empty("hostfs",		Opt_hostfs),
+	{}
+};
+
+static int hostfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
+{
+	struct hostfs_fs_info *fsi = fc->s_fs_info;
+	struct fs_parse_result result;
+	char *host_root, *tmp_root;
+	int opt;
+
+	opt = fs_parse(fc, hostfs_param_specs, param, &result);
+	if (opt < 0)
+		return opt;
+
+	switch (opt) {
+	case Opt_hostfs:
+		host_root = param->string;
+		if (!*host_root)
+			break;
+		tmp_root = kasprintf(GFP_KERNEL, "%s%s",
+				     fsi->host_root_path, host_root);
+		if (!tmp_root)
+			return -ENOMEM;
+		kfree(fsi->host_root_path);
+		fsi->host_root_path = tmp_root;
+		break;
+	}
+
+	return 0;
+}
+
+static int hostfs_parse_monolithic(struct fs_context *fc, void *data)
+{
+	struct hostfs_fs_info *fsi = fc->s_fs_info;
+	char *tmp_root, *host_root = (char *)data;
+
+	/* NULL is printed as '(null)' by printf(): avoid that. */
+	if (host_root == NULL)
+		return 0;
+
+	tmp_root = kasprintf(GFP_KERNEL, "%s%s", fsi->host_root_path, host_root);
+	if (!tmp_root)
+		return -ENOMEM;
+	kfree(fsi->host_root_path);
+	fsi->host_root_path = tmp_root;
+	return 0;
+}
+
+static int hostfs_fc_get_tree(struct fs_context *fc)
+{
+	return get_tree_nodev(fc, hostfs_fill_super);
+}
+
+static void hostfs_fc_free(struct fs_context *fc)
+{
+	struct hostfs_fs_info *fsi = fc->s_fs_info;
+
+	if (!fsi)
+		return;
+
+	kfree(fsi->host_root_path);
+	kfree(fsi);
+}
+
+static const struct fs_context_operations hostfs_context_ops = {
+	.parse_monolithic = hostfs_parse_monolithic,
+	.parse_param	= hostfs_parse_param,
+	.get_tree	= hostfs_fc_get_tree,
+	.free		= hostfs_fc_free,
+};
+
+static int hostfs_init_fs_context(struct fs_context *fc)
+{
+	struct hostfs_fs_info *fsi;
+
+	fsi = kzalloc_obj(*fsi);
+	if (!fsi)
+		return -ENOMEM;
+
+	fsi->host_root_path = kasprintf(GFP_KERNEL, "%s/", root_ino);
+	if (!fsi->host_root_path) {
+		kfree(fsi);
+		return -ENOMEM;
+	}
+	fc->s_fs_info = fsi;
+	fc->ops = &hostfs_context_ops;
+	return 0;
+}
+
+static void hostfs_kill_sb(struct super_block *s)
+{
+	kill_anon_super(s);
+	kfree(s->s_fs_info);
+}
+
+static struct file_system_type hostfs_type = {
+	.owner			= THIS_MODULE,
+	.name			= "hostfs",
+	.init_fs_context	= hostfs_init_fs_context,
+	.kill_sb		= hostfs_kill_sb,
+	.fs_flags		= 0,
+};
+MODULE_ALIAS_FS("hostfs");
+
+static int __init init_hostfs(void)
+{
+	hostfs_inode_cache = KMEM_CACHE(hostfs_inode_info, 0);
+	if (!hostfs_inode_cache)
+		return -ENOMEM;
+	return register_filesystem(&hostfs_type);
+}
+
+static void __exit exit_hostfs(void)
+{
+	unregister_filesystem(&hostfs_type);
+	kmem_cache_destroy(hostfs_inode_cache);
+}
+
+module_init(init_hostfs)
+module_exit(exit_hostfs)
+MODULE_DESCRIPTION("User-Mode Linux Host filesystem");
+MODULE_LICENSE("GPL");
diff --git a/fs/hostfs/hostfs_user.c b/fs/hostfs/hostfs_user.c
new file mode 100644
index 000000000..3bcd9f35e
--- /dev/null
+++ b/fs/hostfs/hostfs_user.c
@@ -0,0 +1,421 @@
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ * Licensed under the GPL
+ */
+
+#include <stdio.h>
+#include <stddef.h>
+#include <unistd.h>
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <sys/vfs.h>
+#include <sys/syscall.h>
+#include "hostfs.h"
+#include <utime.h>
+
+static void statx_to_hostfs(const struct statx *buf, struct hostfs_stat *p)
+{
+	p->ino = buf->stx_ino;
+	p->mode = buf->stx_mode;
+	p->nlink = buf->stx_nlink;
+	p->uid = buf->stx_uid;
+	p->gid = buf->stx_gid;
+	p->size = buf->stx_size;
+	p->atime.tv_sec = buf->stx_atime.tv_sec;
+	p->atime.tv_nsec = buf->stx_atime.tv_nsec;
+	p->ctime.tv_sec = buf->stx_ctime.tv_sec;
+	p->ctime.tv_nsec = buf->stx_ctime.tv_nsec;
+	p->mtime.tv_sec = buf->stx_mtime.tv_sec;
+	p->mtime.tv_nsec = buf->stx_mtime.tv_nsec;
+	if (buf->stx_mask & STATX_BTIME) {
+		p->btime.tv_sec = buf->stx_btime.tv_sec;
+		p->btime.tv_nsec = buf->stx_btime.tv_nsec;
+	} else {
+		memset(&p->btime, 0, sizeof(p->btime));
+	}
+	p->blksize = buf->stx_blksize;
+	p->blocks = buf->stx_blocks;
+	p->rdev.maj = buf->stx_rdev_major;
+	p->rdev.min = buf->stx_rdev_minor;
+	p->dev.maj = buf->stx_dev_major;
+	p->dev.min = buf->stx_dev_minor;
+}
+
+int stat_file(const char *path, struct hostfs_stat *p, int fd)
+{
+	struct statx buf;
+	int flags = AT_SYMLINK_NOFOLLOW;
+
+	if (fd >= 0) {
+		flags |= AT_EMPTY_PATH;
+		path = "";
+	}
+
+	if ((statx(fd, path, flags, STATX_BASIC_STATS | STATX_BTIME, &buf)) < 0)
+		return -errno;
+
+	statx_to_hostfs(&buf, p);
+	return 0;
+}
+
+int access_file(char *path, int r, int w, int x)
+{
+	int mode = 0;
+
+	if (r)
+		mode = R_OK;
+	if (w)
+		mode |= W_OK;
+	if (x)
+		mode |= X_OK;
+	if (access(path, mode) != 0)
+		return -errno;
+	else return 0;
+}
+
+int open_file(char *path, int r, int w, int append)
+{
+	int mode = 0, fd;
+
+	if (r && !w)
+		mode = O_RDONLY;
+	else if (!r && w)
+		mode = O_WRONLY;
+	else if (r && w)
+		mode = O_RDWR;
+	else panic("Impossible mode in open_file");
+
+	if (append)
+		mode |= O_APPEND;
+	fd = open64(path, mode);
+	if (fd < 0)
+		return -errno;
+	else return fd;
+}
+
+void *open_dir(char *path, int *err_out)
+{
+	DIR *dir;
+
+	dir = opendir(path);
+	*err_out = errno;
+
+	return dir;
+}
+
+void seek_dir(void *stream, unsigned long long pos)
+{
+	DIR *dir = stream;
+
+	seekdir(dir, pos);
+}
+
+char *read_dir(void *stream, unsigned long long *pos_out,
+	       unsigned long long *ino_out, int *len_out,
+	       unsigned int *type_out)
+{
+	DIR *dir = stream;
+	struct dirent *ent;
+
+	ent = readdir(dir);
+	if (ent == NULL)
+		return NULL;
+	*len_out = strlen(ent->d_name);
+	*ino_out = ent->d_ino;
+	*type_out = ent->d_type;
+	*pos_out = ent->d_off;
+	return ent->d_name;
+}
+
+int read_file(int fd, unsigned long long *offset, char *buf, int len)
+{
+	int n;
+
+	n = pread64(fd, buf, len, *offset);
+	if (n < 0)
+		return -errno;
+	*offset += n;
+	return n;
+}
+
+int write_file(int fd, unsigned long long *offset, const char *buf, int len)
+{
+	int n;
+
+	n = pwrite64(fd, buf, len, *offset);
+	if (n < 0)
+		return -errno;
+	*offset += n;
+	return n;
+}
+
+int lseek_file(int fd, long long offset, int whence)
+{
+	int ret;
+
+	ret = lseek64(fd, offset, whence);
+	if (ret < 0)
+		return -errno;
+	return 0;
+}
+
+int fsync_file(int fd, int datasync)
+{
+	int ret;
+	if (datasync)
+		ret = fdatasync(fd);
+	else
+		ret = fsync(fd);
+
+	if (ret < 0)
+		return -errno;
+	return 0;
+}
+
+int replace_file(int oldfd, int fd)
+{
+	return dup2(oldfd, fd);
+}
+
+void close_file(void *stream)
+{
+	close(*((int *) stream));
+}
+
+void close_dir(void *stream)
+{
+	closedir(stream);
+}
+
+int file_create(char *name, int mode)
+{
+	int fd;
+
+	fd = open64(name, O_CREAT | O_RDWR, mode);
+	if (fd < 0)
+		return -errno;
+	return fd;
+}
+
+int set_attr(const char *file, struct hostfs_iattr *attrs, int fd)
+{
+	struct hostfs_stat st;
+	struct timeval times[2];
+	int err, ma;
+
+	if (attrs->ia_valid & HOSTFS_ATTR_MODE) {
+		if (fd >= 0) {
+			if (fchmod(fd, attrs->ia_mode) != 0)
+				return -errno;
+		} else if (chmod(file, attrs->ia_mode) != 0) {
+			return -errno;
+		}
+	}
+	if (attrs->ia_valid & HOSTFS_ATTR_UID) {
+		if (fd >= 0) {
+			if (fchown(fd, attrs->ia_uid, -1))
+				return -errno;
+		} else if (chown(file, attrs->ia_uid, -1)) {
+			return -errno;
+		}
+	}
+	if (attrs->ia_valid & HOSTFS_ATTR_GID) {
+		if (fd >= 0) {
+			if (fchown(fd, -1, attrs->ia_gid))
+				return -errno;
+		} else if (chown(file, -1, attrs->ia_gid)) {
+			return -errno;
+		}
+	}
+	if (attrs->ia_valid & HOSTFS_ATTR_SIZE) {
+		if (fd >= 0) {
+			if (ftruncate(fd, attrs->ia_size))
+				return -errno;
+		} else if (truncate(file, attrs->ia_size)) {
+			return -errno;
+		}
+	}
+
+	/*
+	 * Update accessed and/or modified time, in two parts: first set
+	 * times according to the changes to perform, and then call futimes()
+	 * or utimes() to apply them.
+	 */
+	ma = (HOSTFS_ATTR_ATIME_SET | HOSTFS_ATTR_MTIME_SET);
+	if (attrs->ia_valid & ma) {
+		err = stat_file(file, &st, fd);
+		if (err != 0)
+			return err;
+
+		times[0].tv_sec = st.atime.tv_sec;
+		times[0].tv_usec = st.atime.tv_nsec / 1000;
+		times[1].tv_sec = st.mtime.tv_sec;
+		times[1].tv_usec = st.mtime.tv_nsec / 1000;
+
+		if (attrs->ia_valid & HOSTFS_ATTR_ATIME_SET) {
+			times[0].tv_sec = attrs->ia_atime.tv_sec;
+			times[0].tv_usec = attrs->ia_atime.tv_nsec / 1000;
+		}
+		if (attrs->ia_valid & HOSTFS_ATTR_MTIME_SET) {
+			times[1].tv_sec = attrs->ia_mtime.tv_sec;
+			times[1].tv_usec = attrs->ia_mtime.tv_nsec / 1000;
+		}
+
+		if (fd >= 0) {
+			if (futimes(fd, times) != 0)
+				return -errno;
+		} else if (utimes(file, times) != 0) {
+			return -errno;
+		}
+	}
+
+	/* Note: ctime is not handled */
+	if (attrs->ia_valid & (HOSTFS_ATTR_ATIME | HOSTFS_ATTR_MTIME)) {
+		err = stat_file(file, &st, fd);
+		attrs->ia_atime = st.atime;
+		attrs->ia_mtime = st.mtime;
+		if (err != 0)
+			return err;
+	}
+	return 0;
+}
+
+int make_symlink(const char *from, const char *to)
+{
+	int err;
+
+	err = symlink(to, from);
+	if (err)
+		return -errno;
+	return 0;
+}
+
+int unlink_file(const char *file)
+{
+	int err;
+
+	err = unlink(file);
+	if (err)
+		return -errno;
+	return 0;
+}
+
+int do_mkdir(const char *file, int mode)
+{
+	int err;
+
+	err = mkdir(file, mode);
+	if (err)
+		return -errno;
+	return 0;
+}
+
+int hostfs_do_rmdir(const char *file)
+{
+	int err;
+
+	err = rmdir(file);
+	if (err)
+		return -errno;
+	return 0;
+}
+
+int do_mknod(const char *file, int mode, unsigned int major, unsigned int minor)
+{
+	int err;
+
+	err = mknod(file, mode, os_makedev(major, minor));
+	if (err)
+		return -errno;
+	return 0;
+}
+
+int link_file(const char *to, const char *from)
+{
+	int err;
+
+	err = link(to, from);
+	if (err)
+		return -errno;
+	return 0;
+}
+
+int hostfs_do_readlink(char *file, char *buf, int size)
+{
+	int n;
+
+	n = readlink(file, buf, size);
+	if (n < 0)
+		return -errno;
+	if (n < size)
+		buf[n] = '\0';
+	return n;
+}
+
+int rename_file(char *from, char *to)
+{
+	int err;
+
+	err = rename(from, to);
+	if (err < 0)
+		return -errno;
+	return 0;
+}
+
+int rename2_file(char *from, char *to, unsigned int flags)
+{
+	int err;
+
+#ifndef SYS_renameat2
+#  ifdef __x86_64__
+#    define SYS_renameat2 316
+#  endif
+#  ifdef __i386__
+#    define SYS_renameat2 353
+#  endif
+#endif
+
+#ifdef SYS_renameat2
+	err = syscall(SYS_renameat2, AT_FDCWD, from, AT_FDCWD, to, flags);
+	if (err < 0) {
+		if (errno != ENOSYS)
+			return -errno;
+		else
+			return -EINVAL;
+	}
+	return 0;
+#else
+	return -EINVAL;
+#endif
+}
+
+int do_statfs(char *root, long *bsize_out, long long *blocks_out,
+	      long long *bfree_out, long long *bavail_out,
+	      long long *files_out, long long *ffree_out,
+	      void *fsid_out, int fsid_size, long *namelen_out)
+{
+	struct statfs64 buf;
+	int err;
+
+	err = statfs64(root, &buf);
+	if (err < 0)
+		return -errno;
+
+	*bsize_out = buf.f_bsize;
+	*blocks_out = buf.f_blocks;
+	*bfree_out = buf.f_bfree;
+	*bavail_out = buf.f_bavail;
+	*files_out = buf.f_files;
+	*ffree_out = buf.f_ffree;
+	memcpy(fsid_out, &buf.f_fsid,
+	       sizeof(buf.f_fsid) > fsid_size ? fsid_size :
+	       sizeof(buf.f_fsid));
+	*namelen_out = buf.f_namelen;
+
+	return 0;
+}
diff --git a/fs/hostfs/hostfs_user_exp.c b/fs/hostfs/hostfs_user_exp.c
new file mode 100644
index 000000000..250c91c55
--- /dev/null
+++ b/fs/hostfs/hostfs_user_exp.c
@@ -0,0 +1,28 @@
+#include <linux/module.h>
+#include "hostfs.h"
+
+EXPORT_SYMBOL_GPL(stat_file);
+EXPORT_SYMBOL_GPL(access_file);
+EXPORT_SYMBOL_GPL(open_file);
+EXPORT_SYMBOL_GPL(open_dir);
+EXPORT_SYMBOL_GPL(seek_dir);
+EXPORT_SYMBOL_GPL(read_dir);
+EXPORT_SYMBOL_GPL(read_file);
+EXPORT_SYMBOL_GPL(write_file);
+EXPORT_SYMBOL_GPL(lseek_file);
+EXPORT_SYMBOL_GPL(fsync_file);
+EXPORT_SYMBOL_GPL(replace_file);
+EXPORT_SYMBOL_GPL(close_file);
+EXPORT_SYMBOL_GPL(close_dir);
+EXPORT_SYMBOL_GPL(file_create);
+EXPORT_SYMBOL_GPL(set_attr);
+EXPORT_SYMBOL_GPL(make_symlink);
+EXPORT_SYMBOL_GPL(unlink_file);
+EXPORT_SYMBOL_GPL(do_mkdir);
+EXPORT_SYMBOL_GPL(hostfs_do_rmdir);
+EXPORT_SYMBOL_GPL(do_mknod);
+EXPORT_SYMBOL_GPL(link_file);
+EXPORT_SYMBOL_GPL(hostfs_do_readlink);
+EXPORT_SYMBOL_GPL(rename_file);
+EXPORT_SYMBOL_GPL(rename2_file);
+EXPORT_SYMBOL_GPL(do_statfs);