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Subject[experimental PATCH] ovl: get rid of d_real()
On Fri, Sep 15, 2017 at 10:06:24AM +0200, Miklos Szeredi wrote:
> And, btw. I also hate all the hacks we need to do in the VFS for the
> sake of overlayfs. It may actually end up all being removed and all
> the stacking moved to overlayfs; that's something I'd really like to
> look at. All of these hacks are there because overlayfs lets the
> open file be owned by the underlying filesystem, which is good for
> performance and results in simpler code in overlayfs, but may not
> actually be worth it.

And here's the prototype. Poof, d_real() is gone.

It definitely has got problems, but just maybe it can be made better than the
current mess. It *does* solve the ro-rw inconsistency for normal reads (not
mmaps).

Thanks,
Miklos

---
fs/overlayfs/Makefile | 2
fs/overlayfs/file.c | 167 +++++++++++++++++++++++++++++++++++++++++++++++
fs/overlayfs/inode.c | 1
fs/overlayfs/overlayfs.h | 5 +
fs/overlayfs/super.c | 65 ------------------
5 files changed, 174 insertions(+), 66 deletions(-)

--- a/fs/overlayfs/Makefile
+++ b/fs/overlayfs/Makefile
@@ -4,4 +4,4 @@

obj-$(CONFIG_OVERLAY_FS) += overlay.o

-overlay-objs := super.o namei.o util.o inode.o dir.o readdir.o copy_up.o
+overlay-objs := super.o namei.o util.o inode.o dir.o file.o readdir.o copy_up.o
--- /dev/null
+++ b/fs/overlayfs/file.c
@@ -0,0 +1,167 @@
+/*
+ * 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 "overlayfs.h"
+
+static int ovl_check_append_only(struct inode *inode, int flag)
+{
+ /*
+ * This test was moot in vfs may_open() because overlay inode does
+ * not have the S_APPEND flag, so re-check on real upper inode
+ */
+ if (IS_APPEND(inode)) {
+ if ((flag & O_ACCMODE) != O_RDONLY && !(flag & O_APPEND))
+ return -EPERM;
+ if (flag & O_TRUNC)
+ return -EPERM;
+ }
+
+ return 0;
+}
+
+static int ovl_open(struct inode *inode, struct file *file)
+{
+ struct dentry *dentry = file->f_path.dentry;
+ int err;
+
+ err = ovl_open_maybe_copy_up(dentry, file->f_flags);
+ if (!err)
+ err = ovl_check_append_only(d_inode(ovl_dentry_real(dentry)),
+ file->f_flags);
+
+ return err;
+}
+
+static rwf_t ovl_iocb_to_rwf(struct kiocb *iocb)
+{
+ int ifl = iocb->ki_flags;
+ rwf_t flags = 0;
+
+ if (ifl & IOCB_NOWAIT)
+ flags |= RWF_NOWAIT;
+ if (ifl & IOCB_HIPRI)
+ flags |= RWF_HIPRI;
+ if (ifl & IOCB_DSYNC)
+ flags |= RWF_DSYNC;
+ if (ifl & IOCB_SYNC)
+ flags |= RWF_SYNC;
+
+ return flags;
+}
+
+static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter)
+{
+ struct file *file = iocb->ki_filp;
+ struct path realpath;
+ struct file *realfile;
+ ssize_t ret;
+
+ ovl_path_real(file->f_path.dentry, &realpath);
+ realfile = dentry_open(&realpath, file->f_flags, current_cred());
+ if (IS_ERR(realfile))
+ return PTR_ERR(realfile);
+
+ ret = vfs_iter_read(realfile, iter, &iocb->ki_pos,
+ ovl_iocb_to_rwf(iocb));
+
+ fput(realfile);
+
+ return ret;
+}
+
+static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
+{
+ struct file *file = iocb->ki_filp;
+ struct path realpath;
+ struct file *realfile;
+ ssize_t ret;
+
+ ovl_path_real(file->f_path.dentry, &realpath);
+ realfile = dentry_open(&realpath, file->f_flags, current_cred());
+ if (IS_ERR(realfile))
+ return PTR_ERR(realfile);
+
+ ret = vfs_iter_write(realfile, iter, &iocb->ki_pos,
+ ovl_iocb_to_rwf(iocb));
+
+ fput(realfile);
+
+ return ret;
+}
+
+static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
+{
+ struct path realpath;
+ struct file *realfile;
+ int ret;
+
+ ovl_path_real(file->f_path.dentry, &realpath);
+ realfile = dentry_open(&realpath, file->f_flags, current_cred());
+ if (IS_ERR(realfile))
+ return PTR_ERR(realfile);
+
+ ret = vfs_fsync_range(realfile, start, end, datasync);
+
+ fput(realfile);
+
+ return ret;
+}
+
+static loff_t ovl_llseek(struct file *file, loff_t offset, int whence)
+{
+ struct inode *realinode = d_inode(ovl_dentry_real(file->f_path.dentry));
+
+ return generic_file_llseek_size(file, offset, whence,
+ realinode->i_sb->s_maxbytes,
+ i_size_read(realinode));
+}
+
+static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
+{
+ struct inode *inode = file_inode(file);
+ struct path realpath;
+ struct file *realfile;
+ struct inode *realinode;
+ int err;
+
+ ovl_path_real(file->f_path.dentry, &realpath);
+ realinode = d_inode(realpath.dentry);
+
+ realfile = dentry_open(&realpath, file->f_flags, current_cred());
+ if (IS_ERR(realfile))
+ return PTR_ERR(realfile);
+
+ err = -ENODEV;
+ if (!realfile->f_op->mmap)
+ goto out;
+
+ file->f_mapping = realfile->f_mapping;
+ if (inode->i_mapping == &inode->i_data)
+ inode->i_mapping = realinode->i_mapping;
+
+ err = -EBUSY;
+ if (inode->i_mapping != realinode->i_mapping)
+ goto out;
+
+ err = call_mmap(realfile, vma);
+out:
+ fput(realfile);
+
+ return err;
+}
+
+const struct file_operations ovl_file_operations = {
+ .open = ovl_open,
+ .read_iter = ovl_read_iter,
+ .write_iter = ovl_write_iter,
+ .fsync = ovl_fsync,
+ .llseek = ovl_llseek,
+ .mmap = ovl_mmap,
+};
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -436,6 +436,7 @@ static void ovl_fill_inode(struct inode
switch (mode & S_IFMT) {
case S_IFREG:
inode->i_op = &ovl_file_inode_operations;
+ inode->i_fop = &ovl_file_operations;
break;

case S_IFDIR:
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -9,6 +9,8 @@

#include <linux/kernel.h>
#include <linux/uuid.h>
+#include <linux/xattr.h>
+#include <linux/fs.h>

enum ovl_path_type {
__OVL_PATH_UPPER = (1 << 0),
@@ -309,6 +311,9 @@ int ovl_create_real(struct inode *dir, s
struct dentry *hardlink, bool debug);
int ovl_cleanup(struct inode *dir, struct dentry *dentry);

+/* 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);
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -52,69 +52,6 @@ static void ovl_dentry_release(struct de
}
}

-static int ovl_check_append_only(struct inode *inode, int flag)
-{
- /*
- * This test was moot in vfs may_open() because overlay inode does
- * not have the S_APPEND flag, so re-check on real upper inode
- */
- if (IS_APPEND(inode)) {
- if ((flag & O_ACCMODE) != O_RDONLY && !(flag & O_APPEND))
- return -EPERM;
- if (flag & O_TRUNC)
- return -EPERM;
- }
-
- return 0;
-}
-
-static struct dentry *ovl_d_real(struct dentry *dentry,
- const struct inode *inode,
- unsigned int open_flags, unsigned int flags)
-{
- struct dentry *real;
- int err;
-
- if (flags & D_REAL_UPPER)
- return ovl_dentry_upper(dentry);
-
- if (!d_is_reg(dentry)) {
- if (!inode || inode == d_inode(dentry))
- return dentry;
- goto bug;
- }
-
- if (open_flags) {
- err = ovl_open_maybe_copy_up(dentry, open_flags);
- if (err)
- return ERR_PTR(err);
- }
-
- real = ovl_dentry_upper(dentry);
- if (real && (!inode || inode == d_inode(real))) {
- if (!inode) {
- err = ovl_check_append_only(d_inode(real), open_flags);
- if (err)
- return ERR_PTR(err);
- }
- return real;
- }
-
- real = ovl_dentry_lower(dentry);
- if (!real)
- goto bug;
-
- /* Handle recursion */
- real = d_real(real, inode, open_flags, 0);
-
- if (!inode || inode == d_inode(real))
- return real;
-bug:
- WARN(1, "ovl_d_real(%pd4, %s:%lu): real dentry not found\n", dentry,
- inode ? inode->i_sb->s_id : "NULL", inode ? inode->i_ino : 0);
- return dentry;
-}
-
static int ovl_dentry_revalidate(struct dentry *dentry, unsigned int flags)
{
struct ovl_entry *oe = dentry->d_fsdata;
@@ -158,12 +95,10 @@ static int ovl_dentry_weak_revalidate(st

static const struct dentry_operations ovl_dentry_operations = {
.d_release = ovl_dentry_release,
- .d_real = ovl_d_real,
};

static const struct dentry_operations ovl_reval_dentry_operations = {
.d_release = ovl_dentry_release,
- .d_real = ovl_d_real,
.d_revalidate = ovl_dentry_revalidate,
.d_weak_revalidate = ovl_dentry_weak_revalidate,
};
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