1 files changed, 75 insertions, 0 deletions
diff --git a/fs/fat/misc.c b/fs/fat/misc.c
index 2eca073fe785..fce0a76f3f1e 100644
--- a/fs/fat/misc.c
+++ b/fs/fat/misc.c
@@ -7,6 +7,7 @@
  */
 
 #include "fat.h"
+#include <linux/iversion.h>
 
 /*
  * fat_fs_error reports a file system problem that might indicate fa data
@@ -265,6 +266,80 @@ void fat_time_unix2fat(struct msdos_sb_info *sbi, struct timespec64 *ts,
 }
 EXPORT_SYMBOL_GPL(fat_time_unix2fat);
 
+static inline struct timespec64 fat_timespec64_trunc_2secs(struct timespec64 ts)
+{
+	return (struct timespec64){ ts.tv_sec & ~1ULL, 0 };
+}
+/*
+ * truncate the various times with appropriate granularity:
+ *   root inode:
+ *     all times always 0
+ *   all other inodes:
+ *     mtime - 2 seconds
+ *     ctime
+ *       msdos - 2 seconds
+ *       vfat  - 10 milliseconds
+ *     atime - 24 hours (00:00:00 in local timezone)
+ */
+int fat_truncate_time(struct inode *inode, struct timespec64 *now, int flags)
+{
+	struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
+	struct timespec64 ts;
+
+	if (inode->i_ino == MSDOS_ROOT_INO)
+		return 0;
+
+	if (now == NULL) {
+		now = &ts;
+		ts = current_time(inode);
+	}
+
+	if (flags & S_ATIME) {
+		/* to localtime */
+		time64_t seconds = now->tv_sec - fat_tz_offset(sbi);
+		s32 remainder;
+
+		div_s64_rem(seconds, SECS_PER_DAY, &remainder);
+		/* to day boundary, and back to unix time */
+		seconds = seconds + fat_tz_offset(sbi) - remainder;
+
+		inode->i_atime = (struct timespec64){ seconds, 0 };
+	}
+	if (flags & S_CTIME) {
+		if (sbi->options.isvfat)
+			inode->i_ctime = timespec64_trunc(*now, 10000000);
+		else
+			inode->i_ctime = fat_timespec64_trunc_2secs(*now);
+	}
+	if (flags & S_MTIME)
+		inode->i_mtime = fat_timespec64_trunc_2secs(*now);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(fat_truncate_time);
+
+int fat_update_time(struct inode *inode, struct timespec64 *now, int flags)
+{
+	int iflags = I_DIRTY_TIME;
+	bool dirty = false;
+
+	if (inode->i_ino == MSDOS_ROOT_INO)
+		return 0;
+
+	fat_truncate_time(inode, now, flags);
+	if (flags & S_VERSION)
+		dirty = inode_maybe_inc_iversion(inode, false);
+	if ((flags & (S_ATIME | S_CTIME | S_MTIME)) &&
+	    !(inode->i_sb->s_flags & SB_LAZYTIME))
+		dirty = true;
+
+	if (dirty)
+		iflags |= I_DIRTY_SYNC;
+	__mark_inode_dirty(inode, iflags);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(fat_update_time);
+
 int fat_sync_bhs(struct buffer_head **bhs, int nr_bhs)
 {
 	int i, err = 0;