[RFC PATCH v3 4/5] exfat: make crtime user-settable using ptime

[koraynilay <koray.fra@gmail.com>]

Since exFAT supports user-settable file creation timestamps, map
provenance time (ptime) to exFAT file creation time (crtime) using the
newly introduced ptime API (in commit "vfs: add provenance time
(ptime)").

To do this, implement exfat_fileattr_set(), set .fileattr_set to it for
both file_inode and dir_inode operations and update exfat_fileattr_get()
and exfat_getattr().

The timestamp is now retrievable by using file_getattr() or statx(), and
is settable by using file_setattr() with the FS_XFLAG_PTIME flag.

Assisted-by: Gemini:3.8-flash-high antigravity-cli-1.4.7
Signed-off-by: koraynilay <koray.fra@gmail.com>
---
 fs/exfat/exfat_fs.h |  2 ++
 fs/exfat/file.c     | 36 +++++++++++++++++++++++++++++++++++-
 fs/exfat/namei.c    |  1 +
 3 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
index eee573d1697c..aff96afa258a 100644
--- a/fs/exfat/exfat_fs.h
+++ b/fs/exfat/exfat_fs.h
@@ -619,6 +619,8 @@ int exfat_getattr(const struct mnt_idmap *idmap, const struct path *path,
 		  unsigned int query_flags);
 struct file_kattr;
 int exfat_fileattr_get(struct dentry *dentry, struct file_kattr *fa);
+int exfat_fileattr_set(const struct mnt_idmap *idmap, struct dentry *dentry,
+		       struct file_kattr *fa);
 int exfat_file_fsync(struct file *file, loff_t start, loff_t end, int datasync);
 long exfat_ioctl(struct file *filp, unsigned int cmd, unsigned long arg);
 long exfat_compat_ioctl(struct file *filp, unsigned int cmd,
diff --git a/fs/exfat/file.c b/fs/exfat/file.c
index 1386149916bb..70e226cb4ab7 100644
--- a/fs/exfat/file.c
+++ b/fs/exfat/file.c
@@ -384,15 +384,20 @@ int exfat_getattr(const struct mnt_idmap *idmap, const struct path *path,
 
 	generic_fillattr(idmap, request_mask, inode, stat);
 	exfat_truncate_atime(&stat->atime);
-	stat->result_mask |= STATX_BTIME;
+	stat->result_mask |= (STATX_BTIME | STATX_PTIME);
 	stat->btime.tv_sec = ei->i_crtime.tv_sec;
 	stat->btime.tv_nsec = ei->i_crtime.tv_nsec;
+	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;
 }
 
 int exfat_fileattr_get(struct dentry *dentry, struct file_kattr *fa)
 {
+	struct inode *inode = d_backing_inode(dentry);
+	struct exfat_inode_info *ei = EXFAT_I(inode);
+
 	/*
 	 * exFAT compares filenames through an upcase table, so lookup
 	 * is always case-insensitive. Long names are stored in UTF-16
@@ -400,6 +405,11 @@ int exfat_fileattr_get(struct dentry *dentry, struct file_kattr *fa)
 	 */
 	fa->fsx_xflags |= FS_XFLAG_CASEFOLD;
 	fa->flags |= FS_CASEFOLD_FL;
+
+	fa->fsx_ptime.tv_sec = ei->i_crtime.tv_sec;
+	fa->fsx_ptime.tv_nsec = ei->i_crtime.tv_nsec;
+	fa->fsx_xflags |= FS_XFLAG_PTIME;
+
 	return 0;
 }
 
@@ -485,6 +495,29 @@ int exfat_setattr(const struct mnt_idmap *idmap, struct dentry *dentry,
 	return error;
 }
 
+int exfat_fileattr_set(const struct mnt_idmap *idmap, struct dentry *dentry,
+		      struct file_kattr *fa)
+{
+	struct inode *inode = d_backing_inode(dentry);
+	struct exfat_inode_info *ei = EXFAT_I(inode);
+
+	if (fileattr_has_fsx_mask(fa, FS_XFLAG_PTIME))
+		return -EOPNOTSUPP;
+
+	if (fa->flags & ~FS_CASEFOLD_FL)
+		return -EOPNOTSUPP;
+
+	if (fa->fsx_xflags & FS_XFLAG_PTIME) {
+		ei->i_crtime.tv_sec = fa->fsx_ptime.tv_sec;
+		ei->i_crtime.tv_nsec = fa->fsx_ptime.tv_nsec;
+	}
+
+	inode_set_ctime_current(inode);
+	mark_inode_dirty(inode);
+
+	return 0;
+}
+
 /*
  * modified ioctls from fat/file.c by Welmer Almesberger
  */
@@ -1110,4 +1143,5 @@ const struct inode_operations exfat_file_inode_operations = {
 	.setattr	= exfat_setattr,
 	.getattr	= exfat_getattr,
 	.fileattr_get	= exfat_fileattr_get,
+	.fileattr_set	= exfat_fileattr_set,
 };
diff --git a/fs/exfat/namei.c b/fs/exfat/namei.c
index 68ddb9c5504f..15ec7f1942c8 100644
--- a/fs/exfat/namei.c
+++ b/fs/exfat/namei.c
@@ -1349,4 +1349,5 @@ const struct inode_operations exfat_dir_inode_operations = {
 	.setattr	= exfat_setattr,
 	.getattr	= exfat_getattr,
 	.fileattr_get	= exfat_fileattr_get,
+	.fileattr_set	= exfat_fileattr_set,
 };
-- 
2.56.0