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Miklos Szeredi
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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: Miklos Szeredi <mszeredi@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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‎fs/overlayfs/Makefile

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -4,5 +4,5 @@
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obj-$(CONFIG_OVERLAY_FS) += overlay.o
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7-
overlay-objs := super.o namei.o util.o inode.o dir.o readdir.o copy_up.o \
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export.o
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overlay-objs := super.o namei.o util.o inode.o file.o dir.o readdir.o \
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copy_up.o export.o

‎fs/overlayfs/file.c

Lines changed: 76 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,76 @@
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/*
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* Copyright (C) 2017 Red Hat, Inc.
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 as published by
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* the Free Software Foundation.
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*/
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#include <linux/cred.h>
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#include <linux/file.h>
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#include <linux/xattr.h>
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#include "overlayfs.h"
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static struct file *ovl_open_realfile(const struct file *file)
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{
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struct inode *inode = file_inode(file);
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struct inode *upperinode = ovl_inode_upper(inode);
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struct inode *realinode = upperinode ?: ovl_inode_lower(inode);
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struct file *realfile;
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const struct cred *old_cred;
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old_cred = ovl_override_creds(inode->i_sb);
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realfile = open_with_fake_path(&file->f_path, file->f_flags | O_NOATIME,
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realinode, current_cred());
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revert_creds(old_cred);
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pr_debug("open(%p[%pD2/%c], 0%o) -> (%p, 0%o)\n",
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file, file, upperinode ? 'u' : 'l', file->f_flags,
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realfile, IS_ERR(realfile) ? 0 : realfile->f_flags);
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return realfile;
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}
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static int ovl_open(struct inode *inode, struct file *file)
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{
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struct dentry *dentry = file_dentry(file);
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struct file *realfile;
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int err;
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err = ovl_open_maybe_copy_up(dentry, file->f_flags);
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if (err)
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return err;
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/* No longer need these flags, so don't pass them on to underlying fs */
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file->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
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realfile = ovl_open_realfile(file);
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if (IS_ERR(realfile))
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return PTR_ERR(realfile);
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file->private_data = realfile;
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return 0;
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}
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static int ovl_release(struct inode *inode, struct file *file)
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{
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fput(file->private_data);
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return 0;
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}
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static loff_t ovl_llseek(struct file *file, loff_t offset, int whence)
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{
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struct inode *realinode = ovl_inode_real(file_inode(file));
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return generic_file_llseek_size(file, offset, whence,
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realinode->i_sb->s_maxbytes,
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i_size_read(realinode));
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}
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const struct file_operations ovl_file_operations = {
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.open = ovl_open,
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.release = ovl_release,
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.llseek = ovl_llseek,
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};

‎fs/overlayfs/inode.c

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -535,6 +535,7 @@ static void ovl_fill_inode(struct inode *inode, umode_t mode, dev_t rdev,
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switch (mode & S_IFMT) {
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case S_IFREG:
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inode->i_op = &ovl_file_inode_operations;
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inode->i_fop = &ovl_file_operations;
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break;
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case S_IFDIR:

‎fs/overlayfs/overlayfs.h

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -377,6 +377,9 @@ struct dentry *ovl_create_real(struct inode *dir, struct dentry *newdentry,
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int ovl_cleanup(struct inode *dir, struct dentry *dentry);
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struct dentry *ovl_create_temp(struct dentry *workdir, struct ovl_cattr *attr);
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/* file.c */
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extern const struct file_operations ovl_file_operations;
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/* copy_up.c */
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int ovl_copy_up(struct dentry *dentry);
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int ovl_copy_up_flags(struct dentry *dentry, int flags);

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