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Commit d1d04ef8 authored by Miklos Szeredi's avatar Miklos Szeredi
Browse files

ovl: stack file ops 



Implement file operations on a regular overlay file.  The underlying file
is opened separately and cached in ->private_data.

It might be worth making an exception for such files when accounting in
nr_file to confirm to userspace expectations.  We are only adding a small
overhead (248bytes for the struct file) since the real inode and dentry are
pinned by overlayfs anyway.

This patch doesn't have any effect, since the vfs will use d_real() to find
the real underlying file to open.  The patch at the end of the series will
actually enable this functionality.

AV: make it use open_with_fake_path(), don't mess with override_creds

SzM: still need to mess with override_creds() until no fs uses
current_cred() in their open method.

Signed-off-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent e8c985ba

fs/overlayfs/Makefile

+2 −2
Original line number Diff line number Diff line
@@ -4,5 +4,5 @@ 


obj-$(CONFIG_OVERLAY_FS) += overlay.o



overlay-objs := super.o namei.o util.o inode.o dir.o readdir.o copy_up.o \

		export.o
 
overlay-objs := super.o namei.o util.o inode.o file.o dir.o readdir.o \

		copy_up.o export.o

fs/overlayfs/file.c

0 → 100644
+76 −0
Original line number Diff line number Diff line 
/*

 * Copyright (C) 2017 Red Hat, Inc.

 *

 * This program is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 as published by

 * the Free Software Foundation.

 */



#include <linux/cred.h>

#include <linux/file.h>

#include <linux/xattr.h>

#include "overlayfs.h"



static struct file *ovl_open_realfile(const struct file *file)

{

	struct inode *inode = file_inode(file);

	struct inode *upperinode = ovl_inode_upper(inode);

	struct inode *realinode = upperinode ?: ovl_inode_lower(inode);

	struct file *realfile;

	const struct cred *old_cred;



	old_cred = ovl_override_creds(inode->i_sb);

	realfile = open_with_fake_path(&file->f_path, file->f_flags | O_NOATIME,

				       realinode, current_cred());

	revert_creds(old_cred);



	pr_debug("open(%p[%pD2/%c], 0%o) -> (%p, 0%o)\n",

		 file, file, upperinode ? 'u' : 'l', file->f_flags,

		 realfile, IS_ERR(realfile) ? 0 : realfile->f_flags);



	return realfile;

}



static int ovl_open(struct inode *inode, struct file *file)

{

	struct dentry *dentry = file_dentry(file);

	struct file *realfile;

	int err;



	err = ovl_open_maybe_copy_up(dentry, file->f_flags);

	if (err)

		return err;



	/* No longer need these flags, so don't pass them on to underlying fs */

	file->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);



	realfile = ovl_open_realfile(file);

	if (IS_ERR(realfile))

		return PTR_ERR(realfile);



	file->private_data = realfile;



	return 0;

}



static int ovl_release(struct inode *inode, struct file *file)

{

	fput(file->private_data);



	return 0;

}



static loff_t ovl_llseek(struct file *file, loff_t offset, int whence)

{

	struct inode *realinode = ovl_inode_real(file_inode(file));



	return generic_file_llseek_size(file, offset, whence,

					realinode->i_sb->s_maxbytes,

					i_size_read(realinode));

}



const struct file_operations ovl_file_operations = {

	.open		= ovl_open,

	.release	= ovl_release,

	.llseek		= ovl_llseek,

};

fs/overlayfs/inode.c

+1 −0
Original line number Diff line number Diff line
@@ -535,6 +535,7 @@ static void ovl_fill_inode(struct inode *inode, umode_t mode, dev_t rdev, 
	switch (mode & S_IFMT) {

	case S_IFREG:

		inode->i_op = &ovl_file_inode_operations;

		inode->i_fop = &ovl_file_operations;

		break;



	case S_IFDIR:

fs/overlayfs/overlayfs.h

+3 −0
Original line number Diff line number Diff line
@@ -377,6 +377,9 @@ struct dentry *ovl_create_real(struct inode *dir, struct dentry *newdentry, 
int ovl_cleanup(struct inode *dir, struct dentry *dentry);

struct dentry *ovl_create_temp(struct dentry *workdir, struct ovl_cattr *attr);



/* file.c */

extern const struct file_operations ovl_file_operations;



/* copy_up.c */

int ovl_copy_up(struct dentry *dentry);

int ovl_copy_up_flags(struct dentry *dentry, int flags);