[PATCH 4.19.y] erofs: derive atime instead of leaving it empty

[Gao Xiang]

From: Gao Xiang <hsiangkao at redhat.com>

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@aol.com
[ Gao Xiang: It'd be better to backport for user-friendly concern. ]
Fixes: 431339ba9042 ("staging: erofs: add inode operations")
Cc: stable <stable at vger.kernel.org> # 4.19+
Reported-by: nl6720 <nl6720 at gmail.com>
Reviewed-by: Chao Yu <yuchao0 at huawei.com>
[ Gao Xiang: Manually backport to 4.19.y due to trivial conflicts. ]
Signed-off-by: Gao Xiang <hsiangkao at redhat.com>
---
 drivers/staging/erofs/inode.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/drivers/staging/erofs/inode.c b/drivers/staging/erofs/inode.c
index 7448744cc515..12a5be95457f 100644
--- a/drivers/staging/erofs/inode.c
+++ b/drivers/staging/erofs/inode.c
@@ -53,11 +53,9 @@ static int read_inode(struct inode *inode, void *data)
 		i_gid_write(inode, le32_to_cpu(v2->i_gid));
 		set_nlink(inode, le32_to_cpu(v2->i_nlink));
 
-		/* ns timestamp */
-		inode->i_mtime.tv_sec = inode->i_ctime.tv_sec =
-			le64_to_cpu(v2->i_ctime);
-		inode->i_mtime.tv_nsec = inode->i_ctime.tv_nsec =
-			le32_to_cpu(v2->i_ctime_nsec);
+		/* extended inode has its own timestamp */
+		inode->i_ctime.tv_sec = le64_to_cpu(v2->i_ctime);
+		inode->i_ctime.tv_nsec = le32_to_cpu(v2->i_ctime_nsec);
 
 		inode->i_size = le64_to_cpu(v2->i_size);
 	} else if (__inode_version(advise) == EROFS_INODE_LAYOUT_V1) {
@@ -83,11 +81,9 @@ static int read_inode(struct inode *inode, void *data)
 		i_gid_write(inode, le16_to_cpu(v1->i_gid));
 		set_nlink(inode, le16_to_cpu(v1->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(v1->i_size);
 	} else {
@@ -97,6 +93,11 @@ static int read_inode(struct inode *inode, void *data)
 		return -EIO;
 	}
 
+	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;
+
 	/* measure inode.i_blocks as the generic filesystem */
 	inode->i_blocks = ((inode->i_size - 1) >> 9) + 1;
 	return 0;
-- 
2.24.0