From: Darrick J. Wong <djwong@xxxxxxxxxx>
generic/192 fails like this even before we start adding iomap code:
--- tests/generic/192.out 2025-04-30 16:20:44.512675591 -0700
+++ tests/generic/192.out.bad 2025-07-06 22:26:11.666015735 -0700
@@ -1,5 +1,6 @@
QA output created by 192
sleep for 5 seconds
test
-delta1 is in range
+delta1 has value of 0
+delta1 is NOT in range 5 .. 7
delta2 is in range
The cause of this regression is that the timestamp comparisons account
only for seconds, not nanoseconds. If a write came in 100ms after the
last read but still in the same second, then we fail to update atime on
a subsequent read.
Fix this by converting the timespecs to doubles so that we can include
the nanoseconds component, and then perform the comparison in floating
point mode.
Cc: <linux-ext4@xxxxxxxxxxxxxxx> # v1.43
Fixes: 81cbf1ef4f5dab ("misc: add fuse2fs, a FUSE server for e2fsprogs")
Signed-off-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
---
misc/fuse2fs.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index ab3efea66d3def..b7201f7c8ed185 100644
--- a/misc/fuse2fs.c
+++ b/misc/fuse2fs.c
@@ -461,6 +461,7 @@ static int update_atime(ext2_filsys fs, ext2_ino_t ino)
errcode_t err;
struct ext2_inode_large inode, *pinode;
struct timespec atime, mtime, now;
+ double datime, dmtime, dnow;
if (!(fs->flags & EXT2_FLAG_RW))
return 0;
@@ -472,11 +473,17 @@ static int update_atime(ext2_filsys fs, ext2_ino_t ino)
EXT4_INODE_GET_XTIME(i_atime, &atime, pinode);
EXT4_INODE_GET_XTIME(i_mtime, &mtime, pinode);
get_now(&now);
+
+ datime = atime.tv_sec + ((double)atime.tv_nsec / 1000000000);
+ dmtime = mtime.tv_sec + ((double)mtime.tv_nsec / 1000000000);
+ dnow = now.tv_sec + ((double)now.tv_nsec / 1000000000);
+
/*
* If atime is newer than mtime and atime hasn't been updated in thirty
- * seconds, skip the atime update. Same idea as Linux "relatime".
+ * seconds, skip the atime update. Same idea as Linux "relatime". Use
+ * doubles to account for nanosecond resolution.
*/
- if (atime.tv_sec >= mtime.tv_sec && atime.tv_sec >= now.tv_sec - 30)
+ if (datime >= dmtime && datime >= dnow - 30)
return 0;
EXT4_INODE_SET_XTIME(i_atime, &now, &inode);
