The patch titled
Subject: fat: add renameat2 RENAME_EXCHANGE flag support
has been added to the -mm mm-nonmm-unstable branch. Its filename is
fat-add-renameat2-rename_exchange-flag-support.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fat-add-renameat2-rename_exchange-flag-support.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Javier Martinez Canillas <javierm@xxxxxxxxxx>
Subject: fat: add renameat2 RENAME_EXCHANGE flag support
Date: Fri, 10 Jun 2022 09:57:20 +0200
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.
Link: https://lkml.kernel.org/r/20220610075721.1182745-4-javierm@xxxxxxxxxx
Signed-off-by: Javier Martinez Canillas <javierm@xxxxxxxxxx>
Acked-by: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
Cc: Alexander Larsson <alexl@xxxxxxxxxx>
Cc: Christian Kellner <ckellner@xxxxxxxxxx>
Cc: Chung-Chiang Cheng <cccheng@xxxxxxxxxxxx>
Cc: Colin Walters <walters@xxxxxxxxxx>
Cc: Lennart Poettering <lennart@xxxxxxxxxxxxxx>
Cc: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
Cc: Peter Jones <pjones@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/fat/namei_vfat.c | 123 +++++++++++++++++++++++++++++++++++++++++-
1 file changed, 122 insertions(+), 1 deletion(-)
--- a/fs/fat/namei_vfat.c~fat-add-renameat2-rename_exchange-flag-support
+++ a/fs/fat/namei_vfat.c
@@ -1042,13 +1042,134 @@ error_inode:
goto out;
}
+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 void vfat_move_nlink(struct inode *src, struct inode *dst)
+{
+ drop_nlink(src);
+ inc_nlink(dst);
+}
+
+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_de(old_inode, &old_dotdot_bh,
+ &old_dotdot_de);
+ if (err)
+ goto out;
+
+ err = vfat_get_dotdot_de(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;
+
+ vfat_exchange_ipos(old_inode, new_inode, old_i_pos, new_i_pos);
+
+ err = vfat_sync_ipos(old_dir, new_inode);
+ if (err)
+ goto error_exchange;
+ 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_de(new_dir, old_inode, old_dotdot_bh,
+ old_dotdot_de);
+ if (err)
+ goto error_old_dotdot;
+ }
+ if (new_dotdot_de) {
+ err = vfat_update_dotdot_de(old_dir, new_inode, new_dotdot_bh,
+ new_dotdot_de);
+ if (err)
+ goto error_new_dotdot;
+ }
+
+ /* if cross directory and only one is a directory, adjust nlink */
+ if (!old_dotdot_de != !new_dotdot_de) {
+ if (old_dotdot_de)
+ vfat_move_nlink(old_dir, new_dir);
+ else
+ vfat_move_nlink(new_dir, old_dir);
+ }
+
+ 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:
+ if (new_dotdot_de) {
+ corrupt |= vfat_update_dotdot_de(new_dir, new_inode,
+ new_dotdot_bh, new_dotdot_de);
+ }
+
+error_old_dotdot:
+ if (old_dotdot_de) {
+ corrupt |= vfat_update_dotdot_de(old_dir, old_inode,
+ old_dotdot_bh, old_dotdot_de);
+ }
+
+error_exchange:
+ 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,
+ "%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);
}
_
Patches currently in -mm which might be from javierm@xxxxxxxxxx are
fat-add-a-vfat_rename2-and-make-existing-rename-callback-a-helper.patch
fat-add-renameat2-rename_exchange-flag-support.patch
selftests-filesystems-add-a-vfat-rename_exchange-test.patch
