In preparation for factoring out some backing file io helpers from
overlayfs, move backing_file_open() into a new file fs/backing-file.c
and header.
Add a MAINTAINERS entry for stackable filesystems and add a Kconfig
FS_STACK which stackable filesystems need to select.
For now, the backing_file struct, the backing_file alloc/free functions
and the backing_file_real_path() accessor remain internal to file_table.c.
We may change that in the future.
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
MAINTAINERS | 9 +++++++
fs/Kconfig | 4 +++
fs/Makefile | 1 +
fs/backing-file.c | 48 ++++++++++++++++++++++++++++++++++++
fs/open.c | 38 ----------------------------
fs/overlayfs/Kconfig | 1 +
fs/overlayfs/file.c | 1 +
include/linux/backing-file.h | 17 +++++++++++++
include/linux/fs.h | 3 ---
9 files changed, 81 insertions(+), 41 deletions(-)
create mode 100644 fs/backing-file.c
create mode 100644 include/linux/backing-file.h
diff --git a/MAINTAINERS b/MAINTAINERS
index 788be9ab5b73..9115a4f0dec7 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8186,6 +8186,15 @@ S: Supported
F: fs/iomap/
F: include/linux/iomap.h
+FILESYSTEMS [STACKABLE]
+M: Miklos Szeredi <miklos@xxxxxxxxxx>
+M: Amir Goldstein <amir73il@xxxxxxxxx>
+L: linux-fsdevel@xxxxxxxxxxxxxxx
+L: linux-unionfs@xxxxxxxxxxxxxxx
+S: Maintained
+F: fs/backing-file.c
+F: include/linux/backing-file.h
+
FINTEK F75375S HARDWARE MONITOR AND FAN CONTROLLER DRIVER
M: Riku Voipio <riku.voipio@xxxxxx>
L: linux-hwmon@xxxxxxxxxxxxxxx
diff --git a/fs/Kconfig b/fs/Kconfig
index fd1f655b4f1f..c47fa4eb9282 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -18,6 +18,10 @@ config VALIDATE_FS_PARSER
config FS_IOMAP
bool
+# Stackable filesystems
+config FS_STACK
+ bool
+
config BUFFER_HEAD
bool
diff --git a/fs/Makefile b/fs/Makefile
index 75522f88e763..a6962c588962 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -39,6 +39,7 @@ obj-$(CONFIG_COMPAT_BINFMT_ELF) += compat_binfmt_elf.o
obj-$(CONFIG_BINFMT_ELF_FDPIC) += binfmt_elf_fdpic.o
obj-$(CONFIG_BINFMT_FLAT) += binfmt_flat.o
+obj-$(CONFIG_FS_STACK) += backing-file.o
obj-$(CONFIG_FS_MBCACHE) += mbcache.o
obj-$(CONFIG_FS_POSIX_ACL) += posix_acl.o
obj-$(CONFIG_NFS_COMMON) += nfs_common/
diff --git a/fs/backing-file.c b/fs/backing-file.c
new file mode 100644
index 000000000000..04b33036f709
--- /dev/null
+++ b/fs/backing-file.c
@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Common helpers for stackable filesystems and backing files.
+ *
+ * Copyright (C) 2023 CTERA Networks.
+ */
+
+#include <linux/fs.h>
+#include <linux/backing-file.h>
+
+#include "internal.h"
+
+/**
+ * backing_file_open - open a backing file for kernel internal use
+ * @user_path: path that the user reuqested to open
+ * @flags: open flags
+ * @real_path: path of the backing file
+ * @cred: credentials for open
+ *
+ * Open a backing file for a stackable filesystem (e.g., overlayfs).
+ * @user_path may be on the stackable filesystem and @real_path on the
+ * underlying filesystem. In this case, we want to be able to return the
+ * @user_path of the stackable filesystem. This is done by embedding the
+ * returned file into a container structure that also stores the stacked
+ * file's path, which can be retrieved using backing_file_user_path().
+ */
+struct file *backing_file_open(const struct path *user_path, int flags,
+ const struct path *real_path,
+ const struct cred *cred)
+{
+ struct file *f;
+ int error;
+
+ f = alloc_empty_backing_file(flags, cred);
+ if (IS_ERR(f))
+ return f;
+
+ path_get(user_path);
+ *backing_file_user_path(f) = *user_path;
+ error = vfs_open(real_path, f);
+ if (error) {
+ fput(f);
+ f = ERR_PTR(error);
+ }
+
+ return f;
+}
+EXPORT_SYMBOL_GPL(backing_file_open);
diff --git a/fs/open.c b/fs/open.c
index d877228d5939..a75054237437 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -1184,44 +1184,6 @@ struct file *kernel_file_open(const struct path *path, int flags,
}
EXPORT_SYMBOL_GPL(kernel_file_open);
-/**
- * backing_file_open - open a backing file for kernel internal use
- * @user_path: path that the user reuqested to open
- * @flags: open flags
- * @real_path: path of the backing file
- * @cred: credentials for open
- *
- * Open a backing file for a stackable filesystem (e.g., overlayfs).
- * @user_path may be on the stackable filesystem and @real_path on the
- * underlying filesystem. In this case, we want to be able to return the
- * @user_path of the stackable filesystem. This is done by embedding the
- * returned file into a container structure that also stores the stacked
- * file's path, which can be retrieved using backing_file_user_path().
- */
-struct file *backing_file_open(const struct path *user_path, int flags,
- const struct path *real_path,
- const struct cred *cred)
-{
- struct file *f;
- int error;
-
- f = alloc_empty_backing_file(flags, cred);
- if (IS_ERR(f))
- return f;
-
- path_get(user_path);
- *backing_file_user_path(f) = *user_path;
- f->f_path = *real_path;
- error = do_dentry_open(f, d_inode(real_path->dentry), NULL);
- if (error) {
- fput(f);
- f = ERR_PTR(error);
- }
-
- return f;
-}
-EXPORT_SYMBOL_GPL(backing_file_open);
-
#define WILL_CREATE(flags) (flags & (O_CREAT | __O_TMPFILE))
#define O_PATH_FLAGS (O_DIRECTORY | O_NOFOLLOW | O_PATH | O_CLOEXEC)
diff --git a/fs/overlayfs/Kconfig b/fs/overlayfs/Kconfig
index fec5020c3495..2ac67e04a6fb 100644
--- a/fs/overlayfs/Kconfig
+++ b/fs/overlayfs/Kconfig
@@ -1,6 +1,7 @@
# SPDX-License-Identifier: GPL-2.0-only
config OVERLAY_FS
tristate "Overlay filesystem support"
+ select FS_STACK
select EXPORTFS
help
An overlay filesystem combines two filesystems - an 'upper' filesystem
diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index 4e46420c8fdd..a6da3eaf6d4f 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -13,6 +13,7 @@
#include <linux/security.h>
#include <linux/mm.h>
#include <linux/fs.h>
+#include <linux/backing-file.h>
#include "overlayfs.h"
#include "../internal.h" /* for sb_init_dio_done_wq */
diff --git a/include/linux/backing-file.h b/include/linux/backing-file.h
new file mode 100644
index 000000000000..55c9e804f780
--- /dev/null
+++ b/include/linux/backing-file.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Common helpers for stackable filesystems and backing files.
+ *
+ * Copyright (C) 2023 CTERA Networks.
+ */
+
+#ifndef _LINUX_BACKING_FILE_H
+#define _LINUX_BACKING_FILE_H
+
+#include <linux/file.h>
+
+struct file *backing_file_open(const struct path *user_path, int flags,
+ const struct path *real_path,
+ const struct cred *cred);
+
+#endif /* _LINUX_BACKING_FILE_H */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 900d0cd55b50..db5d07e6e02e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2575,9 +2575,6 @@ struct file *dentry_open(const struct path *path, int flags,
const struct cred *creds);
struct file *dentry_create(const struct path *path, int flags, umode_t mode,
const struct cred *cred);
-struct file *backing_file_open(const struct path *user_path, int flags,
- const struct path *real_path,
- const struct cred *cred);
struct path *backing_file_user_path(struct file *f);
/*
--
2.34.1
