[PATCH V2 2/4] fat: add functions to update and truncate timestamps appropriately

[Frank Sorenson <sorenson@redhat.com>]

Add the fat-specific inode_operation ->update_time() and
fat_truncate_time() function to truncate the inode timestamps
from 1 nanosecond to the appropriate granularity.

Signed-off-by: Frank Sorenson <sorenson@redhat.com>
---
 fs/fat/fat.h         |  2 ++
 fs/fat/file.c        |  1 +
 fs/fat/inode.c       |  5 ++++
 fs/fat/misc.c        | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 fs/fat/namei_msdos.c |  1 +
 fs/fat/namei_vfat.c  |  1 +
 6 files changed, 85 insertions(+)

diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index 9d7d2d5da28b..3976a2fc787a 100644
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -416,6 +416,8 @@ extern void fat_time_fat2unix(struct msdos_sb_info *sbi, struct timespec64 *ts,
 			      __le16 __time, __le16 __date, u8 time_cs);
 extern void fat_time_unix2fat(struct msdos_sb_info *sbi, struct timespec64 *ts,
 			      __le16 *time, __le16 *date, u8 *time_cs);
+extern int fat_truncate_time(struct inode *inode, struct timespec64 *now, int flags);
+extern int fat_update_time(struct inode *inode, struct timespec64 *now, int flags);
 extern int fat_sync_bhs(struct buffer_head **bhs, int nr_bhs);
 
 int fat_cache_init(void);
diff --git a/fs/fat/file.c b/fs/fat/file.c
index 4f3d72fb1e60..19b6b0566411 100644
--- a/fs/fat/file.c
+++ b/fs/fat/file.c
@@ -552,4 +552,5 @@ EXPORT_SYMBOL_GPL(fat_setattr);
 const struct inode_operations fat_file_inode_operations = {
 	.setattr	= fat_setattr,
 	.getattr	= fat_getattr,
+	.update_time	= fat_update_time,
 };
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index d6b81e31f9f5..3bf60f19b6d3 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -1626,6 +1626,11 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
 	sb->s_magic = MSDOS_SUPER_MAGIC;
 	sb->s_op = &fat_sops;
 	sb->s_export_op = &fat_export_ops;
+	/*
+	 * fat timestamps are complex and truncated by fat itself, so
+	 * we set 1 here to be fast
+	 */
+	sb->s_time_gran = 1;
 	mutex_init(&sbi->nfs_build_inode_lock);
 	ratelimit_state_init(&sbi->ratelimit, DEFAULT_RATELIMIT_INTERVAL,
 			     DEFAULT_RATELIMIT_BURST);
diff --git a/fs/fat/misc.c b/fs/fat/misc.c
index 2eca073fe785..7eb2a756333f 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 = (struct timespec64){ now->tv_sec & ~1, 0 };
+		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;
diff --git a/fs/fat/namei_msdos.c b/fs/fat/namei_msdos.c
index efb8c40c9d27..effbdd5fbf6e 100644
--- a/fs/fat/namei_msdos.c
+++ b/fs/fat/namei_msdos.c
@@ -637,6 +637,7 @@ static const struct inode_operations msdos_dir_inode_operations = {
 	.rename		= msdos_rename,
 	.setattr	= fat_setattr,
 	.getattr	= fat_getattr,
+	.update_time	= fat_update_time,
 };
 
 static void setup(struct super_block *sb)
diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c
index 82cd1e69cbdf..1daa57cf4bf3 100644
--- a/fs/fat/namei_vfat.c
+++ b/fs/fat/namei_vfat.c
@@ -1032,6 +1032,7 @@ static const struct inode_operations vfat_dir_inode_operations = {
 	.rename		= vfat_rename,
 	.setattr	= fat_setattr,
 	.getattr	= fat_getattr,
+	.update_time	= fat_update_time,
 };
 
 static void setup(struct super_block *sb)
-- 
2.14.4