[PATCH v3 0/3] fat: add support for the renameat2 RENAME_EXCHANGE flag

[PATCH v3 0/3] fat: add support for the renameat2 RENAME_EXCHANGE flag

[Javier Martinez Canillas]

Hello,

This series add support for the renameat2 system call RENAME_EXCHANGE flag
(which allows to atomically replace two paths) to the vfat filesystem code.

There are many use cases for this, but we are particularly interested in
making possible for vfat filesystems to be part of OSTree [0] deployments.

Currently OSTree relies on symbolic links to make the deployment updates
an atomic transactional operation. But RENAME_EXCHANGE could be used [1]
to achieve a similar level of robustness when using a vfat filesystem.

Patch #1 is just a preparatory patch to introduce the RENAME_EXCHANGE
support in patch #2 and finally patch #3 adds some kselftests to test it.

This is a v3 that addresses issues pointed out in the second version posted:

https://lkml.org/lkml/2022/5/24/137

[0]: https://github.com/ostreedev/ostree
[1]: https://github.com/ostreedev/ostree/issues/1649

Changes in v3:
- Add a .gitignore for the rename_exchange binary (Muhammad Usama Anjum).
- Include $(KHDR_INCLUDES) instead of hardcoding a relative path in Makefile
  (Muhammad Usama Anjum).

Changes in v2:
- Only update the new_dir inode version and timestamps if != old_dir
  (Alex Larsson).
- Add some helper functions to avoid duplicating code (OGAWA Hirofumi).
- Use braces for multi-lines blocks even if are one statement (OGAWA Hirofumi).
- Mention in commit message that the operation is as transactional as possible
  but within the vfat limitations of not having a journal (Colin Walters).
- Call sync to flush the page cache before checking the file contents
  (Alex Larsson).
- Drop RFC prefix since the patches already got some review.

Javier Martinez Canillas (3):
  fat: add a vfat_rename2() and make existing .rename callback a helper
  fat: add renameat2 RENAME_EXCHANGE flag support
  selftests/filesystems: add a vfat RENAME_EXCHANGE test

 MAINTAINERS                                   |   1 +
 fs/fat/namei_vfat.c                           | 193 +++++++++++++++++-
 tools/testing/selftests/Makefile              |   1 +
 .../selftests/filesystems/fat/.gitignore      |   2 +
 .../selftests/filesystems/fat/Makefile        |   7 +
 .../testing/selftests/filesystems/fat/config  |   2 +
 .../filesystems/fat/rename_exchange.c         |  37 ++++
 .../filesystems/fat/run_fat_tests.sh          |  82 ++++++++
 8 files changed, 318 insertions(+), 7 deletions(-)
 create mode 100644 tools/testing/selftests/filesystems/fat/.gitignore
 create mode 100644 tools/testing/selftests/filesystems/fat/Makefile
 create mode 100644 tools/testing/selftests/filesystems/fat/config
 create mode 100644 tools/testing/selftests/filesystems/fat/rename_exchange.c
 create mode 100755 tools/testing/selftests/filesystems/fat/run_fat_tests.sh

-- 
2.36.1

[PATCH v3 1/3] fat: add a vfat_rename2() and make existing .rename callback a helper

[Javier Martinez Canillas]

Currently vfat only supports the RENAME_NOREPLACE flag which is handled by
the virtual file system layer but doesn't support the RENAME_EXCHANGE flag.

Add a vfat_rename2() function to be used as the .rename callback and move
the current vfat_rename() handler to a helper. This is in preparation for
implementing the RENAME_NOREPLACE flag using a different helper function.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
---

(no changes since v1)

 fs/fat/namei_vfat.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c
index c573314806cf..88ccb2ee3537 100644
--- a/fs/fat/namei_vfat.c
+++ b/fs/fat/namei_vfat.c
@@ -889,9 +889,8 @@ static int vfat_mkdir(struct user_namespace *mnt_userns, struct inode *dir,
 	return err;
 }
 
-static int vfat_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
-		       struct dentry *old_dentry, struct inode *new_dir,
-		       struct dentry *new_dentry, unsigned int flags)
+static int vfat_rename(struct inode *old_dir, struct dentry *old_dentry,
+		       struct inode *new_dir, struct dentry *new_dentry)
 {
 	struct buffer_head *dotdot_bh;
 	struct msdos_dir_entry *dotdot_de;
@@ -902,9 +901,6 @@ static int vfat_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
 	int err, is_dir, update_dotdot, corrupt = 0;
 	struct super_block *sb = old_dir->i_sb;
 
-	if (flags & ~RENAME_NOREPLACE)
-		return -EINVAL;
-
 	old_sinfo.bh = sinfo.bh = dotdot_bh = NULL;
 	old_inode = d_inode(old_dentry);
 	new_inode = d_inode(new_dentry);
@@ -1021,13 +1017,24 @@ static int vfat_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
 	goto out;
 }
 
+static int vfat_rename2(struct user_namespace *mnt_userns, struct inode *old_dir,
+			struct dentry *old_dentry, struct inode *new_dir,
+			struct dentry *new_dentry, unsigned int flags)
+{
+	if (flags & ~RENAME_NOREPLACE)
+		return -EINVAL;
+
+	/* VFS already handled RENAME_NOREPLACE, handle it as a normal rename */
+	return vfat_rename(old_dir, old_dentry, new_dir, new_dentry);
+}
+
 static const struct inode_operations vfat_dir_inode_operations = {
 	.create		= vfat_create,
 	.lookup		= vfat_lookup,
 	.unlink		= vfat_unlink,
 	.mkdir		= vfat_mkdir,
 	.rmdir		= vfat_rmdir,
-	.rename		= vfat_rename,
+	.rename		= vfat_rename2,
 	.setattr	= fat_setattr,
 	.getattr	= fat_getattr,
 	.update_time	= fat_update_time,
-- 
2.36.1

[PATCH v3 2/3] fat: add renameat2 RENAME_EXCHANGE flag support

[Javier Martinez Canillas]

The renameat2 RENAME_EXCHANGE flag allows to atomically exchange two paths
but is currently not supported by the Linux vfat filesystem driver.

Add a vfat_rename_exchange() helper function that implements this support.

The super block lock is acquired during the operation to ensure atomicity,
and in the error path actions made are reversed also with the mutex held.

It makes the operation as transactional as possible, within the limitation
impossed by vfat due not having a journal with logs to replay.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
---

(no changes since v2)

Changes in v2:
- Only update the new_dir inode version and timestamps if != old_dir
  (Alex Larsson).
- Add some helper functions to avoid duplicating code (OGAWA Hirofumi).
- Use braces for multi-lines blocks even if are one statement (OGAWA Hirofumi).
- Mention in commit message that the operation is as transactional as possible
  but within the vfat limitations of not having a journal (Colin Walters).

 fs/fat/namei_vfat.c | 174 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 173 insertions(+), 1 deletion(-)

diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c
index 88ccb2ee3537..97caec8c5207 100644
--- a/fs/fat/namei_vfat.c
+++ b/fs/fat/namei_vfat.c
@@ -1017,13 +1017,185 @@ static int vfat_rename(struct inode *old_dir, struct dentry *old_dentry,
 	goto out;
 }
 
+/* Helpers for vfat_rename_exchange() */
+
+static int vfat_get_dotdot_info(struct inode *inode, struct buffer_head **dotdot_bh,
+				struct msdos_dir_entry **dotdot_de)
+{
+	if (!S_ISDIR(inode->i_mode))
+		return 0;
+
+	return fat_get_dotdot_entry(inode, dotdot_bh, dotdot_de);
+}
+
+static void vfat_exchange_dentries(struct inode *old_inode, struct inode *new_inode,
+				   loff_t old_i_pos, loff_t new_i_pos)
+{
+	fat_detach(old_inode);
+	fat_detach(new_inode);
+
+	fat_attach(old_inode, new_i_pos);
+	fat_attach(new_inode, old_i_pos);
+}
+
+static int vfat_sync_after_exchange(struct inode *dir, struct inode *inode)
+{
+	int err = 0;
+
+	if (IS_DIRSYNC(dir))
+		err = fat_sync_inode(inode);
+	else
+		mark_inode_dirty(inode);
+
+	return err;
+}
+
+static int vfat_update_dotdot_info(struct buffer_head *dotdot_bh, struct msdos_dir_entry *dotdot_de,
+				   struct inode *dir, struct inode *inode)
+{
+	int err = 0;
+
+	fat_set_start(dotdot_de, MSDOS_I(dir)->i_logstart);
+	mark_buffer_dirty_inode(dotdot_bh, inode);
+
+	if (IS_DIRSYNC(dir))
+		err = sync_dirty_buffer(dotdot_bh);
+
+	return err;
+}
+
+static void vfat_update_dir_metadata(struct inode *dir, struct timespec64 *ts)
+{
+	inode_inc_iversion(dir);
+	fat_truncate_time(dir, ts, S_CTIME | S_MTIME);
+
+	if (IS_DIRSYNC(dir))
+		(void)fat_sync_inode(dir);
+	else
+		mark_inode_dirty(dir);
+}
+
+static int vfat_rename_exchange(struct inode *old_dir, struct dentry *old_dentry,
+				struct inode *new_dir, struct dentry *new_dentry)
+{
+	struct buffer_head *old_dotdot_bh = NULL, *new_dotdot_bh = NULL;
+	struct msdos_dir_entry *old_dotdot_de = NULL, *new_dotdot_de = NULL;
+	struct inode *old_inode, *new_inode;
+	struct timespec64 ts = current_time(old_dir);
+	loff_t old_i_pos, new_i_pos;
+	int err, corrupt = 0;
+	struct super_block *sb = old_dir->i_sb;
+
+	old_inode = d_inode(old_dentry);
+	new_inode = d_inode(new_dentry);
+
+	/* Acquire super block lock for the operation to be atomic */
+	mutex_lock(&MSDOS_SB(sb)->s_lock);
+
+	/* if directories are not the same, get ".." info to update */
+	if (old_dir != new_dir) {
+		err = vfat_get_dotdot_info(old_inode, &old_dotdot_bh, &old_dotdot_de);
+		if (err)
+			goto out;
+
+		err = vfat_get_dotdot_info(new_inode, &new_dotdot_bh, &new_dotdot_de);
+		if (err)
+			goto out;
+	}
+
+	old_i_pos = MSDOS_I(old_inode)->i_pos;
+	new_i_pos = MSDOS_I(new_inode)->i_pos;
+
+	/* exchange the two dentries */
+	vfat_exchange_dentries(old_inode, new_inode, old_i_pos, new_i_pos);
+
+	err = vfat_sync_after_exchange(old_dir, new_inode);
+	if (err)
+		goto error_exchange;
+
+	err = vfat_sync_after_exchange(new_dir, old_inode);
+	if (err)
+		goto error_exchange;
+
+	/* update ".." directory entry info */
+	if (old_dotdot_de) {
+		err = vfat_update_dotdot_info(old_dotdot_bh, old_dotdot_de, new_dir, old_inode);
+		if (err)
+			goto error_old_dotdot;
+
+		drop_nlink(old_dir);
+		inc_nlink(new_dir);
+	}
+
+	if (new_dotdot_de) {
+		err = vfat_update_dotdot_info(new_dotdot_bh, new_dotdot_de, old_dir, new_inode);
+		if (err)
+			goto error_new_dotdot;
+
+		drop_nlink(new_dir);
+		inc_nlink(old_dir);
+	}
+
+	/* update inode version and timestamps */
+	inode_inc_iversion(old_inode);
+	inode_inc_iversion(new_inode);
+
+	vfat_update_dir_metadata(old_dir, &ts);
+
+	/* if directories are not the same, update new_dir as well */
+	if (old_dir != new_dir)
+		vfat_update_dir_metadata(new_dir, &ts);
+out:
+	brelse(old_dotdot_bh);
+	brelse(new_dotdot_bh);
+	mutex_unlock(&MSDOS_SB(sb)->s_lock);
+
+	return err;
+
+error_new_dotdot:
+	/* data cluster is shared, serious corruption */
+	corrupt = 1;
+
+	if (new_dotdot_de) {
+		corrupt |= vfat_update_dotdot_info(new_dotdot_bh, new_dotdot_de,
+						   new_dir, new_inode);
+	}
+
+error_old_dotdot:
+	/* data cluster is shared, serious corruption */
+	corrupt = 1;
+
+	if (old_dotdot_de) {
+		corrupt |= vfat_update_dotdot_info(old_dotdot_bh, old_dotdot_de,
+						   old_dir, old_inode);
+	}
+
+error_exchange:
+	vfat_exchange_dentries(old_inode, new_inode, new_i_pos, old_i_pos);
+
+	if (corrupt) {
+		corrupt |= fat_sync_inode(old_inode);
+		corrupt |= fat_sync_inode(new_inode);
+	}
+
+	if (corrupt < 0) {
+		fat_fs_error(new_dir->i_sb,
+			     "%s: Filesystem corrupted (i_pos %lld, %lld)",
+			     __func__, old_i_pos, new_i_pos);
+	}
+	goto out;
+}
+
 static int vfat_rename2(struct user_namespace *mnt_userns, struct inode *old_dir,
 			struct dentry *old_dentry, struct inode *new_dir,
 			struct dentry *new_dentry, unsigned int flags)
 {
-	if (flags & ~RENAME_NOREPLACE)
+	if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
 		return -EINVAL;
 
+	if (flags & RENAME_EXCHANGE)
+		return vfat_rename_exchange(old_dir, old_dentry, new_dir, new_dentry);
+
 	/* VFS already handled RENAME_NOREPLACE, handle it as a normal rename */
 	return vfat_rename(old_dir, old_dentry, new_dir, new_dentry);
 }
-- 
2.36.1

[PATCH v3 3/3] selftests/filesystems: add a vfat RENAME_EXCHANGE test

[Javier Martinez Canillas]

Add a test for the renameat2 RENAME_EXCHANGE support in vfat, but split it
in a tool that just does the rename exchange and a script that is run by
the kselftests framework on `make TARGETS="filesystems/fat" kselftest`.

That way the script can be easily extended to test other file operations.

The script creates a 1 MiB disk image, that is then formated with a vfat
filesystem and mounted using a loop device. That way all file operations
are done on an ephemeral filesystem.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
---

Changes in v3:
- Add a .gitignore for the rename_exchange binary (Muhammad Usama Anjum).
- Include $(KHDR_INCLUDES) instead of hardcoding a relative path in Makefile
  (Muhammad Usama Anjum).

Changes in v2:
- Call sync to flush the page cache before checking the file contents
  (Alex Larsson).

 MAINTAINERS                                   |  1 +
 tools/testing/selftests/Makefile              |  1 +
 .../selftests/filesystems/fat/.gitignore      |  2 +
 .../selftests/filesystems/fat/Makefile        |  7 ++
 .../testing/selftests/filesystems/fat/config  |  2 +
 .../filesystems/fat/rename_exchange.c         | 37 +++++++++
 .../filesystems/fat/run_fat_tests.sh          | 82 +++++++++++++++++++
 7 files changed, 132 insertions(+)
 create mode 100644 tools/testing/selftests/filesystems/fat/.gitignore
 create mode 100644 tools/testing/selftests/filesystems/fat/Makefile
 create mode 100644 tools/testing/selftests/filesystems/fat/config
 create mode 100644 tools/testing/selftests/filesystems/fat/rename_exchange.c
 create mode 100755 tools/testing/selftests/filesystems/fat/run_fat_tests.sh

diff --git a/MAINTAINERS b/MAINTAINERS
index 4fdbbd6c1984..158771bb7755 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -20841,6 +20841,7 @@ M:	OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
 S:	Maintained
 F:	Documentation/filesystems/vfat.rst
 F:	fs/fat/
+F:	tools/testing/selftests/filesystems/fat/
 
 VFIO DRIVER
 M:	Alex Williamson <alex.williamson@redhat.com>
diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 0aedcd76cf0f..fc59ad849a90 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -16,6 +16,7 @@ TARGETS += exec
 TARGETS += filesystems
 TARGETS += filesystems/binderfs
 TARGETS += filesystems/epoll
+TARGETS += filesystems/fat
 TARGETS += firmware
 TARGETS += fpu
 TARGETS += ftrace
diff --git a/tools/testing/selftests/filesystems/fat/.gitignore b/tools/testing/selftests/filesystems/fat/.gitignore
new file mode 100644
index 000000000000..b89920ed841c
--- /dev/null
+++ b/tools/testing/selftests/filesystems/fat/.gitignore
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+rename_exchange
diff --git a/tools/testing/selftests/filesystems/fat/Makefile b/tools/testing/selftests/filesystems/fat/Makefile
new file mode 100644
index 000000000000..902033f6ef09
--- /dev/null
+++ b/tools/testing/selftests/filesystems/fat/Makefile
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0
+
+TEST_PROGS := run_fat_tests.sh
+TEST_GEN_PROGS_EXTENDED := rename_exchange
+CFLAGS += -O2 -g -Wall $(KHDR_INCLUDES)
+
+include ../../lib.mk
diff --git a/tools/testing/selftests/filesystems/fat/config b/tools/testing/selftests/filesystems/fat/config
new file mode 100644
index 000000000000..6cf95e787a17
--- /dev/null
+++ b/tools/testing/selftests/filesystems/fat/config
@@ -0,0 +1,2 @@
+CONFIG_BLK_DEV_LOOP=y
+CONFIG_VFAT_FS=y
diff --git a/tools/testing/selftests/filesystems/fat/rename_exchange.c b/tools/testing/selftests/filesystems/fat/rename_exchange.c
new file mode 100644
index 000000000000..e488ad354fce
--- /dev/null
+++ b/tools/testing/selftests/filesystems/fat/rename_exchange.c
@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Program that atomically exchanges two paths using
+ * the renameat2() system call RENAME_EXCHANGE flag.
+ *
+ * Copyright 2022 Red Hat Inc.
+ * Author: Javier Martinez Canillas <javierm@redhat.com>
+ */
+
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+void print_usage(const char *program)
+{
+	printf("Usage: %s [oldpath] [newpath]\n", program);
+	printf("Atomically exchange oldpath and newpath\n");
+}
+
+int main(int argc, char *argv[])
+{
+	int ret;
+
+	if (argc != 3) {
+		print_usage(argv[0]);
+		exit(EXIT_FAILURE);
+	}
+
+	ret = renameat2(AT_FDCWD, argv[1], AT_FDCWD, argv[2], RENAME_EXCHANGE);
+	if (ret) {
+		perror("rename exchange failed");
+		exit(EXIT_FAILURE);
+	}
+
+	exit(EXIT_SUCCESS);
+}
diff --git a/tools/testing/selftests/filesystems/fat/run_fat_tests.sh b/tools/testing/selftests/filesystems/fat/run_fat_tests.sh
new file mode 100755
index 000000000000..7f35dc3d15df
--- /dev/null
+++ b/tools/testing/selftests/filesystems/fat/run_fat_tests.sh
@@ -0,0 +1,82 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Run filesystem operations tests on an 1 MiB disk image that is formatted with
+# a vfat filesystem and mounted in a temporary directory using a loop device.
+#
+# Copyright 2022 Red Hat Inc.
+# Author: Javier Martinez Canillas <javierm@redhat.com>
+
+set -e
+set -u
+set -o pipefail
+
+BASE_DIR="$(dirname $0)"
+TMP_DIR="$(mktemp -d /tmp/fat_tests_tmp.XXXX)"
+IMG_PATH="${TMP_DIR}/fat.img"
+MNT_PATH="${TMP_DIR}/mnt"
+
+cleanup()
+{
+    mountpoint -q "${MNT_PATH}" && unmount_image
+    rm -rf "${TMP_DIR}"
+}
+trap cleanup SIGINT SIGTERM EXIT
+
+create_loopback()
+{
+    touch "${IMG_PATH}"
+    chattr +C "${IMG_PATH}" >/dev/null 2>&1 || true
+
+    truncate -s 1M "${IMG_PATH}"
+    mkfs.vfat "${IMG_PATH}" >/dev/null 2>&1
+}
+
+mount_image()
+{
+    mkdir -p "${MNT_PATH}"
+    sudo mount -o loop "${IMG_PATH}" "${MNT_PATH}"
+}
+
+rename_exchange_test()
+{
+    local rename_exchange="${BASE_DIR}/rename_exchange"
+    local old_path="${MNT_PATH}/old_file"
+    local new_path="${MNT_PATH}/new_file"
+
+    echo old | sudo tee "${old_path}" >/dev/null 2>&1
+    echo new | sudo tee "${new_path}" >/dev/null 2>&1
+    sudo "${rename_exchange}" "${old_path}" "${new_path}" >/dev/null 2>&1
+    sudo sync -f "${MNT_PATH}"
+    grep new "${old_path}" >/dev/null 2>&1
+    grep old "${new_path}" >/dev/null 2>&1
+}
+
+rename_exchange_subdir_test()
+{
+    local rename_exchange="${BASE_DIR}/rename_exchange"
+    local dir_path="${MNT_PATH}/subdir"
+    local old_path="${MNT_PATH}/old_file"
+    local new_path="${dir_path}/new_file"
+
+    sudo mkdir -p "${dir_path}"
+    echo old | sudo tee "${old_path}" >/dev/null 2>&1
+    echo new | sudo tee "${new_path}" >/dev/null 2>&1
+    sudo "${rename_exchange}" "${old_path}" "${new_path}" >/dev/null 2>&1
+    sudo sync -f "${MNT_PATH}"
+    grep new "${old_path}" >/dev/null 2>&1
+    grep old "${new_path}" >/dev/null 2>&1
+}
+
+unmount_image()
+{
+    sudo umount "${MNT_PATH}" &> /dev/null
+}
+
+create_loopback
+mount_image
+rename_exchange_test
+rename_exchange_subdir_test
+unmount_image
+
+exit 0
-- 
2.36.1

Re: [PATCH v3 3/3] selftests/filesystems: add a vfat RENAME_EXCHANGE test

[Muhammad Usama Anjum]

On 5/26/22 6:41 PM, Javier Martinez Canillas wrote:
> Add a test for the renameat2 RENAME_EXCHANGE support in vfat, but split it
> in a tool that just does the rename exchange and a script that is run by
> the kselftests framework on `make TARGETS="filesystems/fat" kselftest`.
> 
> That way the script can be easily extended to test other file operations.
> 
> The script creates a 1 MiB disk image, that is then formated with a vfat
> filesystem and mounted using a loop device. That way all file operations
> are done on an ephemeral filesystem.
> 
> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Muhammad Usama Anjum <usama.anjum@collabora.com>

-- 
Muhammad Usama Anjum

Re: [PATCH v3 2/3] fat: add renameat2 RENAME_EXCHANGE flag support

[OGAWA Hirofumi]

Javier Martinez Canillas <javierm@redhat.com> writes:

> The renameat2 RENAME_EXCHANGE flag allows to atomically exchange two paths
> but is currently not supported by the Linux vfat filesystem driver.
>
> Add a vfat_rename_exchange() helper function that implements this support.
>
> The super block lock is acquired during the operation to ensure atomicity,
> and in the error path actions made are reversed also with the mutex held.
>
> It makes the operation as transactional as possible, within the limitation
> impossed by vfat due not having a journal with logs to replay.

I tweaked your patch (tested only slightly), can you review and merge to
this patch if ok?

Main purpose of me is to consolidate helpers with vfat_rename(), and
tweak coding style to use existent fat codes.

> +	if (old_dir != new_dir) {
> +		err = vfat_get_dotdot_info(old_inode, &old_dotdot_bh, &old_dotdot_de);
> +		if (err)
> +			goto out;
> +
> +		err = vfat_get_dotdot_info(new_inode, &new_dotdot_bh, &new_dotdot_de);
> +		if (err)
> +			goto out;

This should not return -ENOENT here. I tweaked to return -EIO in my patch.

> +	/* update inode version and timestamps */
> +	inode_inc_iversion(old_inode);
> +	inode_inc_iversion(new_inode);

Why do we need to update iversion of those inodes? I couldn't get intent
of this.

> +error_new_dotdot:
> +	/* data cluster is shared, serious corruption */

Sharing data cluster would happen here only if one inode success to sync
and another one failed. Then so I/O error, we would not be able to do
much for it.

Thanks.
-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>


Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
---
 fs/fat/namei_vfat.c |  205 +++++++++++++++++++++------------------------------
 1 file changed, 87 insertions(+), 118 deletions(-)

diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c
index 3e3cd4f..84f95eb 100644
--- a/fs/fat/namei_vfat.c	2022-05-31 16:53:56.987009983 +0900
+++ b/fs/fat/namei_vfat.c	2022-05-31 18:37:30.893473188 +0900
@@ -893,16 +893,55 @@ out:
 	return err;
 }
 
+static int vfat_get_dotdot_de(struct inode *inode, struct buffer_head **bh,
+			      struct msdos_dir_entry **de)
+{
+	if (S_ISDIR(inode->i_mode)) {
+		if (fat_get_dotdot_entry(inode, bh, de))
+			return -EIO;
+	}
+	return 0;
+}
+
+static int vfat_sync_ipos(struct inode *dir, struct inode *inode)
+{
+	if (IS_DIRSYNC(dir))
+		return fat_sync_inode(inode);
+	mark_inode_dirty(inode);
+	return 0;
+}
+
+static int vfat_update_dotdot_de(struct inode *dir, struct inode *inode,
+				 struct buffer_head *dotdot_bh,
+				 struct msdos_dir_entry *dotdot_de)
+{
+	fat_set_start(dotdot_de, MSDOS_I(dir)->i_logstart);
+	mark_buffer_dirty_inode(dotdot_bh, inode);
+	if (IS_DIRSYNC(dir))
+		return sync_dirty_buffer(dotdot_bh);
+	return 0;
+}
+
+static void vfat_update_dir_metadata(struct inode *dir, struct timespec64 *ts)
+{
+	inode_inc_iversion(dir);
+	fat_truncate_time(dir, ts, S_CTIME | S_MTIME);
+	if (IS_DIRSYNC(dir))
+		(void)fat_sync_inode(dir);
+	else
+		mark_inode_dirty(dir);
+}
+
 static int vfat_rename(struct inode *old_dir, struct dentry *old_dentry,
 		       struct inode *new_dir, struct dentry *new_dentry)
 {
 	struct buffer_head *dotdot_bh;
-	struct msdos_dir_entry *dotdot_de;
+	struct msdos_dir_entry *dotdot_de = NULL;
 	struct inode *old_inode, *new_inode;
 	struct fat_slot_info old_sinfo, sinfo;
 	struct timespec64 ts;
 	loff_t new_i_pos;
-	int err, is_dir, update_dotdot, corrupt = 0;
+	int err, is_dir, corrupt = 0;
 	struct super_block *sb = old_dir->i_sb;
 
 	old_sinfo.bh = sinfo.bh = dotdot_bh = NULL;
@@ -913,15 +952,13 @@ static int vfat_rename(struct inode *old
 	if (err)
 		goto out;
 
-	is_dir = S_ISDIR(old_inode->i_mode);
-	update_dotdot = (is_dir && old_dir != new_dir);
-	if (update_dotdot) {
-		if (fat_get_dotdot_entry(old_inode, &dotdot_bh, &dotdot_de)) {
-			err = -EIO;
+	if (old_dir != new_dir) {
+		err = vfat_get_dotdot_de(old_inode, &dotdot_bh, &dotdot_de);
+		if (err)
 			goto out;
-		}
 	}
 
+	is_dir = S_ISDIR(old_inode->i_mode);
 	ts = current_time(old_dir);
 	if (new_inode) {
 		if (is_dir) {
@@ -942,21 +979,15 @@ static int vfat_rename(struct inode *old
 
 	fat_detach(old_inode);
 	fat_attach(old_inode, new_i_pos);
-	if (IS_DIRSYNC(new_dir)) {
-		err = fat_sync_inode(old_inode);
+	err = vfat_sync_ipos(new_dir, old_inode);
+	if (err)
+		goto error_inode;
+
+	if (dotdot_de) {
+		err = vfat_update_dotdot_de(new_dir, old_inode, dotdot_bh,
+					    dotdot_de);
 		if (err)
-			goto error_inode;
-	} else
-		mark_inode_dirty(old_inode);
-
-	if (update_dotdot) {
-		fat_set_start(dotdot_de, MSDOS_I(new_dir)->i_logstart);
-		mark_buffer_dirty_inode(dotdot_bh, old_inode);
-		if (IS_DIRSYNC(new_dir)) {
-			err = sync_dirty_buffer(dotdot_bh);
-			if (err)
-				goto error_dotdot;
-		}
+			goto error_dotdot;
 		drop_nlink(old_dir);
 		if (!new_inode)
  			inc_nlink(new_dir);
@@ -966,12 +997,7 @@ static int vfat_rename(struct inode *old
 	old_sinfo.bh = NULL;
 	if (err)
 		goto error_dotdot;
-	inode_inc_iversion(old_dir);
-	fat_truncate_time(old_dir, &ts, S_CTIME|S_MTIME);
-	if (IS_DIRSYNC(old_dir))
-		(void)fat_sync_inode(old_dir);
-	else
-		mark_inode_dirty(old_dir);
+	vfat_update_dir_metadata(old_dir, &ts);
 
 	if (new_inode) {
 		drop_nlink(new_inode);
@@ -991,10 +1017,9 @@ error_dotdot:
 	/* data cluster is shared, serious corruption */
 	corrupt = 1;
 
-	if (update_dotdot) {
-		fat_set_start(dotdot_de, MSDOS_I(old_dir)->i_logstart);
-		mark_buffer_dirty_inode(dotdot_bh, old_inode);
-		corrupt |= sync_dirty_buffer(dotdot_bh);
+	if (dotdot_de) {
+		corrupt |= vfat_update_dotdot_de(old_dir, old_inode, dotdot_bh,
+						 dotdot_de);
 	}
 error_inode:
 	fat_detach(old_inode);
@@ -1021,66 +1046,18 @@ error_inode:
 	goto out;
 }
 
-/* Helpers for vfat_rename_exchange() */
-
-static int vfat_get_dotdot_info(struct inode *inode, struct buffer_head **dotdot_bh,
-				struct msdos_dir_entry **dotdot_de)
-{
-	if (!S_ISDIR(inode->i_mode))
-		return 0;
-
-	return fat_get_dotdot_entry(inode, dotdot_bh, dotdot_de);
-}
-
-static void vfat_exchange_dentries(struct inode *old_inode, struct inode *new_inode,
-				   loff_t old_i_pos, loff_t new_i_pos)
+static void vfat_exchange_ipos(struct inode *old_inode, struct inode *new_inode,
+			       loff_t old_i_pos, loff_t new_i_pos)
 {
 	fat_detach(old_inode);
 	fat_detach(new_inode);
-
 	fat_attach(old_inode, new_i_pos);
 	fat_attach(new_inode, old_i_pos);
 }
 
-static int vfat_sync_after_exchange(struct inode *dir, struct inode *inode)
-{
-	int err = 0;
-
-	if (IS_DIRSYNC(dir))
-		err = fat_sync_inode(inode);
-	else
-		mark_inode_dirty(inode);
-
-	return err;
-}
-
-static int vfat_update_dotdot_info(struct buffer_head *dotdot_bh, struct msdos_dir_entry *dotdot_de,
-				   struct inode *dir, struct inode *inode)
-{
-	int err = 0;
-
-	fat_set_start(dotdot_de, MSDOS_I(dir)->i_logstart);
-	mark_buffer_dirty_inode(dotdot_bh, inode);
-
-	if (IS_DIRSYNC(dir))
-		err = sync_dirty_buffer(dotdot_bh);
-
-	return err;
-}
-
-static void vfat_update_dir_metadata(struct inode *dir, struct timespec64 *ts)
-{
-	inode_inc_iversion(dir);
-	fat_truncate_time(dir, ts, S_CTIME | S_MTIME);
-
-	if (IS_DIRSYNC(dir))
-		(void)fat_sync_inode(dir);
-	else
-		mark_inode_dirty(dir);
-}
-
-static int vfat_rename_exchange(struct inode *old_dir, struct dentry *old_dentry,
-				struct inode *new_dir, struct dentry *new_dentry)
+static int
+vfat_rename_exchange(struct inode *old_dir, struct dentry *old_dentry,
+		     struct inode *new_dir, struct dentry *new_dentry)
 {
 	struct buffer_head *old_dotdot_bh = NULL, *new_dotdot_bh = NULL;
 	struct msdos_dir_entry *old_dotdot_de = NULL, *new_dotdot_de = NULL;
@@ -1098,11 +1075,13 @@ static int vfat_rename_exchange(struct i
 
 	/* if directories are not the same, get ".." info to update */
 	if (old_dir != new_dir) {
-		err = vfat_get_dotdot_info(old_inode, &old_dotdot_bh, &old_dotdot_de);
+		err = vfat_get_dotdot_de(old_inode, &old_dotdot_bh,
+					 &old_dotdot_de);
 		if (err)
 			goto out;
 
-		err = vfat_get_dotdot_info(new_inode, &new_dotdot_bh, &new_dotdot_de);
+		err = vfat_get_dotdot_de(new_inode, &new_dotdot_bh,
+					 &new_dotdot_de);
 		if (err)
 			goto out;
 	}
@@ -1110,45 +1089,41 @@ static int vfat_rename_exchange(struct i
 	old_i_pos = MSDOS_I(old_inode)->i_pos;
 	new_i_pos = MSDOS_I(new_inode)->i_pos;
 
-	/* exchange the two dentries */
-	vfat_exchange_dentries(old_inode, new_inode, old_i_pos, new_i_pos);
+	vfat_exchange_ipos(old_inode, new_inode, old_i_pos, new_i_pos);
 
-	err = vfat_sync_after_exchange(old_dir, new_inode);
+	err = vfat_sync_ipos(old_dir, new_inode);
 	if (err)
 		goto error_exchange;
-
-	err = vfat_sync_after_exchange(new_dir, old_inode);
+	err = vfat_sync_ipos(new_dir, old_inode);
 	if (err)
 		goto error_exchange;
 
 	/* update ".." directory entry info */
 	if (old_dotdot_de) {
-		err = vfat_update_dotdot_info(old_dotdot_bh, old_dotdot_de, new_dir, old_inode);
+		err = vfat_update_dotdot_de(new_dir, old_inode, old_dotdot_bh,
+					    old_dotdot_de);
 		if (err)
 			goto error_old_dotdot;
-
 		drop_nlink(old_dir);
 		inc_nlink(new_dir);
 	}
 
 	if (new_dotdot_de) {
-		err = vfat_update_dotdot_info(new_dotdot_bh, new_dotdot_de, old_dir, new_inode);
+		err = vfat_update_dotdot_de(old_dir, new_inode, new_dotdot_bh,
+					    new_dotdot_de);
 		if (err)
 			goto error_new_dotdot;
-
 		drop_nlink(new_dir);
 		inc_nlink(old_dir);
 	}
 
-	/* update inode version and timestamps */
 	inode_inc_iversion(old_inode);
 	inode_inc_iversion(new_inode);
-
 	vfat_update_dir_metadata(old_dir, &ts);
-
 	/* if directories are not the same, update new_dir as well */
 	if (old_dir != new_dir)
 		vfat_update_dir_metadata(new_dir, &ts);
+
 out:
 	brelse(old_dotdot_bh);
 	brelse(new_dotdot_bh);
@@ -1157,30 +1132,21 @@ out:
 	return err;
 
 error_new_dotdot:
-	/* data cluster is shared, serious corruption */
-	corrupt = 1;
-
 	if (new_dotdot_de) {
-		corrupt |= vfat_update_dotdot_info(new_dotdot_bh, new_dotdot_de,
-						   new_dir, new_inode);
+		corrupt |= vfat_update_dotdot_de(new_dir, new_inode,
+						 new_dotdot_bh, new_dotdot_de);
 	}
 
 error_old_dotdot:
-	/* data cluster is shared, serious corruption */
-	corrupt = 1;
-
 	if (old_dotdot_de) {
-		corrupt |= vfat_update_dotdot_info(old_dotdot_bh, old_dotdot_de,
-						   old_dir, old_inode);
+		corrupt |= vfat_update_dotdot_de(old_dir, old_inode,
+						 old_dotdot_bh, old_dotdot_de);
 	}
 
 error_exchange:
-	vfat_exchange_dentries(old_inode, new_inode, new_i_pos, old_i_pos);
-
-	if (corrupt) {
-		corrupt |= fat_sync_inode(old_inode);
-		corrupt |= fat_sync_inode(new_inode);
-	}
+	vfat_exchange_ipos(old_inode, new_inode, new_i_pos, old_i_pos);
+	corrupt |= vfat_sync_ipos(new_dir, new_inode);
+	corrupt |= vfat_sync_ipos(old_dir, old_inode);
 
 	if (corrupt < 0) {
 		fat_fs_error(new_dir->i_sb,
@@ -1190,15 +1156,18 @@ error_exchange:
 	goto out;
 }
 
-static int vfat_rename2(struct user_namespace *mnt_userns, struct inode *old_dir,
+static int vfat_rename2(struct user_namespace *mnt_userns,
+			struct inode *old_dir,
 			struct dentry *old_dentry, struct inode *new_dir,
 			struct dentry *new_dentry, unsigned int flags)
 {
 	if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
 		return -EINVAL;
 
-	if (flags & RENAME_EXCHANGE)
-		return vfat_rename_exchange(old_dir, old_dentry, new_dir, new_dentry);
+	if (flags & RENAME_EXCHANGE) {
+		return vfat_rename_exchange(old_dir, old_dentry,
+					    new_dir, new_dentry);
+	}
 
 	/* VFS already handled RENAME_NOREPLACE, handle it as a normal rename */
 	return vfat_rename(old_dir, old_dentry, new_dir, new_dentry);
_

Re: [PATCH v3 2/3] fat: add renameat2 RENAME_EXCHANGE flag support

[Javier Martinez Canillas]

Hello OGAWA,

Thanks a lot for your feedback and comments.

On 5/31/22 11:51, OGAWA Hirofumi wrote:
> Javier Martinez Canillas <javierm@redhat.com> writes:
> 
>> The renameat2 RENAME_EXCHANGE flag allows to atomically exchange two paths
>> but is currently not supported by the Linux vfat filesystem driver.
>>
>> Add a vfat_rename_exchange() helper function that implements this support.
>>
>> The super block lock is acquired during the operation to ensure atomicity,
>> and in the error path actions made are reversed also with the mutex held.
>>
>> It makes the operation as transactional as possible, within the limitation
>> impossed by vfat due not having a journal with logs to replay.
> 
> I tweaked your patch (tested only slightly), can you review and merge to
> this patch if ok?
>

Your changes make a lot of sense to me and from a quick glance they look OK
to me. I'll look at them in more detail when merging the changes for a v4.
 
> Main purpose of me is to consolidate helpers with vfat_rename(), and
> tweak coding style to use existent fat codes.
>

Indeed. What do you think of the following plan for v4 ?

1) Keep patch "fat: add a vfat_rename2() and make existing .rename callback a helper"
   as the first patch of the series.
2) Add a patch #2 with your authorship that adds the helper and use them in the
   vfat_rename() function.
3) Make this patch "fat: add renameat2 RENAME_EXCHANGE flag support" to be patch #3
   and use the helpers introduced in patch #2.
4) Make patch #4 to not only add a test for RENAME_EXCHANGE but also for renameat()
   and renameat2(..., RENAME_NOREPLACE). That way it will also cover your changes in
   patch #2.

>> +	if (old_dir != new_dir) {
>> +		err = vfat_get_dotdot_info(old_inode, &old_dotdot_bh, &old_dotdot_de);
>> +		if (err)
>> +			goto out;
>> +
>> +		err = vfat_get_dotdot_info(new_inode, &new_dotdot_bh, &new_dotdot_de);
>> +		if (err)
>> +			goto out;
> 
> This should not return -ENOENT here. I tweaked to return -EIO in my patch.
>

Got it. I'm OK with that.

>> +	/* update inode version and timestamps */
>> +	inode_inc_iversion(old_inode);
>> +	inode_inc_iversion(new_inode);
> 
> Why do we need to update iversion of those inodes? I couldn't get intent
> of this.
>

To be honest, I wasn't sure about this either but I saw that the implementation
of RENAME_EXCHANGE in other filesystems did. For example btrfs_rename_exchange().
 
>> +error_new_dotdot:
>> +	/* data cluster is shared, serious corruption */
> 
> Sharing data cluster would happen here only if one inode success to sync
> and another one failed. Then so I/O error, we would not be able to do
> much for it.
>

I see. Thanks for the clarification.

-- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat

Re: [PATCH v3 2/3] fat: add renameat2 RENAME_EXCHANGE flag support

[OGAWA Hirofumi]

Javier Martinez Canillas <javierm@redhat.com> writes:

>> Main purpose of me is to consolidate helpers with vfat_rename(), and
>> tweak coding style to use existent fat codes.
>>
>
> Indeed. What do you think of the following plan for v4 ?
>
> 1) Keep patch "fat: add a vfat_rename2() and make existing .rename callback a helper"
>    as the first patch of the series.
> 2) Add a patch #2 with your authorship that adds the helper and use them in the
>    vfat_rename() function.
> 3) Make this patch "fat: add renameat2 RENAME_EXCHANGE flag support" to be patch #3
>    and use the helpers introduced in patch #2.
> 4) Make patch #4 to not only add a test for RENAME_EXCHANGE but also for renameat()
>    and renameat2(..., RENAME_NOREPLACE). That way it will also cover your changes in
>    patch #2.

I don't care much about it because whole is not big (in short, I'm ok
with even one patch), so the point is the patches should be able to
bisect easily if separated.

>>> +	/* update inode version and timestamps */
>>> +	inode_inc_iversion(old_inode);
>>> +	inode_inc_iversion(new_inode);
>> 
>> Why do we need to update iversion of those inodes? I couldn't get intent
>> of this.
>>
>
> To be honest, I wasn't sure about this either but I saw that the implementation
> of RENAME_EXCHANGE in other filesystems did. For example btrfs_rename_exchange().

Ok. If I'm not overlooking, it looks like only btrfs. Please remove
those inode_inc_iversion() for {new,old}_inode.

Thanks.
-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

Re: [PATCH v3 2/3] fat: add renameat2 RENAME_EXCHANGE flag support

[Javier Martinez Canillas]

On 5/31/22 14:41, OGAWA Hirofumi wrote:
> Javier Martinez Canillas <javierm@redhat.com> writes:
> 
>>> Main purpose of me is to consolidate helpers with vfat_rename(), and
>>> tweak coding style to use existent fat codes.
>>>
>>
>> Indeed. What do you think of the following plan for v4 ?
>>
>> 1) Keep patch "fat: add a vfat_rename2() and make existing .rename callback a helper"
>>    as the first patch of the series.
>> 2) Add a patch #2 with your authorship that adds the helper and use them in the
>>    vfat_rename() function.
>> 3) Make this patch "fat: add renameat2 RENAME_EXCHANGE flag support" to be patch #3
>>    and use the helpers introduced in patch #2.
>> 4) Make patch #4 to not only add a test for RENAME_EXCHANGE but also for renameat()
>>    and renameat2(..., RENAME_NOREPLACE). That way it will also cover your changes in
>>    patch #2.
> 
> I don't care much about it because whole is not big (in short, I'm ok
> with even one patch), so the point is the patches should be able to
> bisect easily if separated.
>

Yes, git bisect-ability is why I mentioned that we could do it in separate patches
but I'll integrate your changes now and see what approach I take depending on how
the code looks then.
 
>>>> +	/* update inode version and timestamps */
>>>> +	inode_inc_iversion(old_inode);
>>>> +	inode_inc_iversion(new_inode);
>>>
>>> Why do we need to update iversion of those inodes? I couldn't get intent
>>> of this.
>>>
>>
>> To be honest, I wasn't sure about this either but I saw that the implementation
>> of RENAME_EXCHANGE in other filesystems did. For example btrfs_rename_exchange().
> 
> Ok. If I'm not overlooking, it looks like only btrfs. Please remove
> those inode_inc_iversion() for {new,old}_inode.
>

Sure.

-- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat