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Subject[RFC PATCH 34/35] vfs: simplify d_op->d_real()
Date
The only remaining user of d_real() is file_dentry().

Simplify code related to ->d_real() by:

- remove dead code from overlayfs implementation
- remove the open_flags argument
- expand d_real() helper into file_dentry()
- remove d_real() helper, since there are no callers and makes no sense to
add new ones

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
Documentation/filesystems/Locking | 3 +--
Documentation/filesystems/vfs.txt | 22 +++-------------
fs/overlayfs/super.c | 55 +++++++--------------------------------
include/linux/dcache.h | 24 +----------------
include/linux/fs.h | 7 ++++-
5 files changed, 21 insertions(+), 90 deletions(-)

diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index a4afe96f0112..e1d7e43d302c 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -21,8 +21,7 @@ prototypes:
char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);
struct vfsmount *(*d_automount)(struct path *path);
int (*d_manage)(const struct path *, bool);
- struct dentry *(*d_real)(struct dentry *, const struct inode *,
- unsigned int);
+ struct dentry *(*d_real)(struct dentry *, const struct inode *);

locking rules:
rename_lock ->d_lock may block rcu-walk
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index af54d3651ff8..632d5c58fde9 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -990,8 +990,7 @@ struct dentry_operations {
char *(*d_dname)(struct dentry *, char *, int);
struct vfsmount *(*d_automount)(struct path *);
int (*d_manage)(const struct path *, bool);
- struct dentry *(*d_real)(struct dentry *, const struct inode *,
- unsigned int);
+ struct dentry *(*d_real)(struct dentry *, const struct inode *);
};

d_revalidate: called when the VFS needs to revalidate a dentry. This
@@ -1124,23 +1123,8 @@ struct dentry_operations {
This function is only used if DCACHE_MANAGE_TRANSIT is set on the
dentry being transited from.

- d_real: overlay/union type filesystems implement this method to return one of
- the underlying dentries hidden by the overlay. It is used in three
- different modes:
-
- Called from open it may need to copy-up the file depending on the
- supplied open flags. This mode is selected with a non-zero flags
- argument. In this mode the d_real method can return an error.
-
- Called from file_dentry() it returns the real dentry matching the inode
- argument. The real dentry may be from a lower layer already copied up,
- but still referenced from the file. This mode is selected with a
- non-NULL inode argument. This will always succeed.
-
- With NULL inode and zero flags the topmost real underlying dentry is
- returned. This will always succeed.
-
- This method is never called with both non-NULL inode and non-zero flags.
+ d_real: This is called from file_dentry(). It returns the real dentry
+ matching the inode argument.

Each dentry has a pointer to its parent dentry, as well as a hash list
of child dentries. Child dentries are basically like files in a
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index f2a83fabe2eb..ab1642fcece3 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -80,64 +80,29 @@ static void ovl_dentry_release(struct dentry *dentry)
}
}

-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)
+ const struct inode *inode)
{
struct dentry *real;
- int err;
+
+ if (WARN_ON(!inode))
+ return dentry;

/* It's an overlay file */
- if (inode && d_inode(dentry) == inode)
+ if (d_inode(dentry) == inode)
return dentry;

- if (!d_is_reg(dentry)) {
- if (!inode || inode == d_inode(dentry))
- return dentry;
+ if (!d_is_reg(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);
- }
+ real = ovl_dentry_real(dentry);
+ if (inode == d_inode(real))
return real;
- }
-
- real = ovl_dentry_lower(dentry);
- if (!real)
- goto bug;

/* Handle recursion */
- real = d_real(real, inode, open_flags);
+ if (unlikely(real->d_flags & DCACHE_OP_REAL))
+ return real->d_op->d_real(real, inode);

- 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);
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 129ef05759a9..712cc21c2e6d 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -147,8 +147,7 @@ struct dentry_operations {
char *(*d_dname)(struct dentry *, char *, int);
struct vfsmount *(*d_automount)(struct path *);
int (*d_manage)(const struct path *, bool);
- struct dentry *(*d_real)(struct dentry *, const struct inode *,
- unsigned int);
+ struct dentry *(*d_real)(struct dentry *, const struct inode *);
} ____cacheline_aligned;

/*
@@ -565,27 +564,6 @@ static inline struct dentry *d_backing_dentry(struct dentry *upper)
return upper;
}

-/**
- * d_real - Return the real dentry
- * @dentry: the dentry to query
- * @inode: inode to select the dentry from multiple layers (can be NULL)
- * @flags: open flags to control copy-up behavior
- *
- * If dentry is on a union/overlay, then return the underlying, real dentry.
- * Otherwise return the dentry itself.
- *
- * See also: Documentation/filesystems/vfs.txt
- */
-static inline struct dentry *d_real(struct dentry *dentry,
- const struct inode *inode,
- unsigned int flags)
-{
- if (unlikely(dentry->d_flags & DCACHE_OP_REAL))
- return dentry->d_op->d_real(dentry, inode, flags);
- else
- return dentry;
-}
-
struct name_snapshot {
const unsigned char *name;
unsigned char inline_name[DNAME_INLINE_LEN];
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6db6e83004d6..77403c19dc69 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1234,7 +1234,12 @@ static inline struct inode *file_inode(const struct file *f)

static inline struct dentry *file_dentry(const struct file *file)
{
- return d_real(file->f_path.dentry, file_inode(file), 0);
+ struct dentry *dentry = file->f_path.dentry;
+
+ if (unlikely(dentry->d_flags & DCACHE_OP_REAL))
+ return dentry->d_op->d_real(dentry, file_inode(file));
+ else
+ return dentry;
}

static inline int locks_lock_file_wait(struct file *filp, struct file_lock *fl)
--
2.14.3
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