[PATCH 5.4 106/151] erofs: derive atime instead of leaving it empty

[Greg Kroah-Hartman]

From: Gao Xiang <hsiangkao@xxxxxxxxxx>

commit d3938ee23e97bfcac2e0eb6b356875da73d700df upstream.

EROFS has _only one_ ondisk timestamp (ctime is currently
documented and recorded, we might also record mtime instead
with a new compat feature if needed) for each extended inode
since EROFS isn't mainly for archival purposes so no need to
keep all timestamps on disk especially for Android scenarios
due to security concerns. Also, romfs/cramfs don't have their
own on-disk timestamp, and squashfs only records mtime instead.

Let's also derive access time from ondisk timestamp rather than
leaving it empty, and if mtime/atime for each file are really
needed for specific scenarios as well, we can also use xattrs
to record them then.

Link: https://lore.kernel.org/r/20201031195102.21221-1-hsiangkao@xxxxxxx
[ Gao Xiang: It'd be better to backport for user-friendly concern. ]
Fixes: 431339ba9042 ("staging: erofs: add inode operations")
Cc: stable <stable@xxxxxxxxxxxxxxx> # 4.19+
Reported-by: nl6720 <nl6720@xxxxxxxxx>
Reviewed-by: Chao Yu <yuchao0@xxxxxxxxxx>
Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/erofs/inode.c |   21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

--- a/fs/erofs/inode.c
+++ b/fs/erofs/inode.c
@@ -107,11 +107,9 @@ static struct page *erofs_read_inode(str
 		i_gid_write(inode, le32_to_cpu(die->i_gid));
 		set_nlink(inode, le32_to_cpu(die->i_nlink));
 
-		/* ns timestamp */
-		inode->i_mtime.tv_sec = inode->i_ctime.tv_sec =
-			le64_to_cpu(die->i_ctime);
-		inode->i_mtime.tv_nsec = inode->i_ctime.tv_nsec =
-			le32_to_cpu(die->i_ctime_nsec);
+		/* extended inode has its own timestamp */
+		inode->i_ctime.tv_sec = le64_to_cpu(die->i_ctime);
+		inode->i_ctime.tv_nsec = le32_to_cpu(die->i_ctime_nsec);
 
 		inode->i_size = le64_to_cpu(die->i_size);
 
@@ -149,11 +147,9 @@ static struct page *erofs_read_inode(str
 		i_gid_write(inode, le16_to_cpu(dic->i_gid));
 		set_nlink(inode, le16_to_cpu(dic->i_nlink));
 
-		/* use build time to derive all file time */
-		inode->i_mtime.tv_sec = inode->i_ctime.tv_sec =
-			sbi->build_time;
-		inode->i_mtime.tv_nsec = inode->i_ctime.tv_nsec =
-			sbi->build_time_nsec;
+		/* use build time for compact inodes */
+		inode->i_ctime.tv_sec = sbi->build_time;
+		inode->i_ctime.tv_nsec = sbi->build_time_nsec;
 
 		inode->i_size = le32_to_cpu(dic->i_size);
 		if (erofs_inode_is_data_compressed(vi->datalayout))
@@ -167,6 +163,11 @@ static struct page *erofs_read_inode(str
 		goto err_out;
 	}
 
+	inode->i_mtime.tv_sec = inode->i_ctime.tv_sec;
+	inode->i_atime.tv_sec = inode->i_ctime.tv_sec;
+	inode->i_mtime.tv_nsec = inode->i_ctime.tv_nsec;
+	inode->i_atime.tv_nsec = inode->i_ctime.tv_nsec;
+
 	if (!nblks)
 		/* measure inode.i_blocks as generic filesystems */
 		inode->i_blocks = roundup(inode->i_size, EROFS_BLKSIZ) >> 9;