[PATCH 6/6] exfat: map ptime to exFAT creation time with rename-over

[Sean Smith <defendthedisabled@gmail.com>]

Map ptime to the exFAT creation time field. exFAT creation time
has 10ms precision.

Getattr: report creation time as ptime.
Setattr: write ptime to i_crtime.
Rename-over: save target creation time before __exfat_rename, restore
  after. Preserves creation time across atomic saves.

Signed-off-by: Sean Smith <DefendTheDisabled@gmail.com>
---
 fs/btrfs/inode.c |  3 ++-
 fs/exfat/file.c  |  9 +++++++++
 fs/exfat/namei.c | 21 ++++++++++++++++++---
 3 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index dce80561a..918dfd4c5 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8715,7 +8715,8 @@ static int btrfs_rename(struct mnt_idmap *idmap,
 		/* Note: if rename fails below, ptime mutation is harmless —
 		 * the source file keeps its previous ptime=0 semantics since
 		 * the rename didn't complete. The in-memory value will be
-		 * overwritten on next inode read from disk. */
+		 * overwritten on next inode read from disk.
+		 */
 
 		ret = btrfs_update_inode(trans, BTRFS_I(old_inode));
 		if (unlikely(ret)) {
diff --git a/fs/exfat/file.c b/fs/exfat/file.c
index 536c8078f..b6438bd79 100644
--- a/fs/exfat/file.c
+++ b/fs/exfat/file.c
@@ -277,6 +277,11 @@ int exfat_getattr(struct mnt_idmap *idmap, const struct path *path,
 	stat->result_mask |= STATX_BTIME;
 	stat->btime.tv_sec = ei->i_crtime.tv_sec;
 	stat->btime.tv_nsec = ei->i_crtime.tv_nsec;
+	if (request_mask & STATX_PTIME) {
+		stat->result_mask |= STATX_PTIME;
+		stat->ptime.tv_sec = ei->i_crtime.tv_sec;
+		stat->ptime.tv_nsec = ei->i_crtime.tv_nsec;
+	}
 	stat->blksize = EXFAT_SB(inode->i_sb)->cluster_size;
 	return 0;
 }
@@ -337,6 +342,10 @@ int exfat_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 	if (attr->ia_valid & ATTR_SIZE)
 		inode_set_mtime_to_ts(inode, inode_set_ctime_current(inode));
 
+	if (attr->ia_valid & ATTR_PTIME) {
+		struct exfat_inode_info *exi = EXFAT_I(inode);
+		exi->i_crtime = attr->ia_ptime;
+	}
 	setattr_copy(idmap, inode, attr);
 	exfat_truncate_inode_atime(inode);
 
diff --git a/fs/exfat/namei.c b/fs/exfat/namei.c
index dfe957493..9c0b59e00 100644
--- a/fs/exfat/namei.c
+++ b/fs/exfat/namei.c
@@ -1262,9 +1262,24 @@ static int exfat_rename(struct mnt_idmap *idmap,
 	old_inode = old_dentry->d_inode;
 	new_inode = new_dentry->d_inode;
 
-	err = __exfat_rename(old_dir, EXFAT_I(old_inode), new_dir, new_dentry);
-	if (err)
-		goto unlock;
+	/* ptime rename-over: save target creation time */
+	{
+		struct timespec64 saved_crtime = {};
+		bool inherit_crtime = false;
+
+		if (new_inode && S_ISREG(old_inode->i_mode) &&
+		    S_ISREG(new_inode->i_mode) && old_inode->i_nlink == 1) {
+			saved_crtime = EXFAT_I(new_inode)->i_crtime;
+			inherit_crtime = true;
+		}
+
+		err = __exfat_rename(old_dir, EXFAT_I(old_inode), new_dir, new_dentry);
+		if (err)
+			goto unlock;
+
+		if (inherit_crtime)
+			EXFAT_I(old_inode)->i_crtime = saved_crtime;
+	}
 
 	inode_inc_iversion(new_dir);
 	simple_rename_timestamp(old_dir, old_dentry, new_dir, new_dentry);
-- 
2.53.0