[PATCH V2 1/2] fat: implement fat_update_time for inode timestamps

[Frank Sorenson <sorenson@xxxxxxxxxx>]

Author: Frank Sorenson <sorenson@xxxxxxxxxx>
Date:   2018-04-03 20:09:35 -0500

    fat: implement fat_update_time for inode timestamps
    
    Add a fat_update_time function to update and truncate
    the inode's timestamps as needed for msdos/vfat filesystems.
    
    If called with the timespec pointer set to NULL, current time
    is used.
    
    Signed-off-by: Frank Sorenson <sorenson@xxxxxxxxxx>

diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index 8fc1093da47d..54d1b08b8ecf 100644
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -410,6 +410,7 @@ extern void fat_time_fat2unix(struct msdos_sb_info *sbi, struct timespec *ts,
 			      __le16 __time, __le16 __date, u8 time_cs);
 extern void fat_time_unix2fat(struct msdos_sb_info *sbi, struct timespec *ts,
 			      __le16 *time, __le16 *date, u8 *time_cs);
+extern int fat_update_time(struct inode *inode, struct timespec *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/misc.c b/fs/fat/misc.c
index f9bdc1e01c98..8df9409bcf66 100644
--- a/fs/fat/misc.c
+++ b/fs/fat/misc.c
@@ -262,6 +262,54 @@ void fat_time_unix2fat(struct msdos_sb_info *sbi, struct timespec *ts,
 }
 EXPORT_SYMBOL_GPL(fat_time_unix2fat);
 
+int fat_update_time(struct inode *inode, struct timespec *now, int flags)
+{
+	int iflags = I_DIRTY_TIME;
+	struct timespec ts;
+
+	if (inode->i_ino == MSDOS_ROOT_INO) {
+		ts = (struct timespec){0, 0};
+		if (flags & S_ATIME)
+			inode->i_atime = ts;
+		if (flags & S_MTIME)
+			inode->i_mtime = ts;
+		if (flags & S_CTIME)
+			inode->i_ctime = ts;
+	} else {
+		struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
+		__le16 time;
+		__le16 date;
+		u8 ctime_cs;
+
+		if (now == NULL) {
+			now = &ts;
+			ts = current_time(inode);
+		}
+
+		if (flags & S_ATIME) {
+			fat_time_unix2fat(sbi, now, &time, &date, NULL);
+			fat_time_fat2unix(sbi, &inode->i_atime, 0, date, 0);
+		}
+		if (flags & S_MTIME) {
+			fat_time_unix2fat(sbi, now, &time, &date, NULL);
+			fat_time_fat2unix(sbi, &inode->i_mtime, time, date, 0);
+		}
+		if (flags & S_CTIME) {
+			fat_time_unix2fat(sbi, now, &time, &date,
+				sbi->options.isvfat ? &ctime_cs :  NULL);
+			fat_time_fat2unix(sbi, &inode->i_ctime, time, date,
+				sbi->options.isvfat ? ctime_cs : 0);
+		}
+	}
+	if ((flags & (S_ATIME | S_CTIME | S_MTIME)) &&
+	    !(inode->i_sb->s_flags & SB_LAZYTIME))
+		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/file.c b/fs/fat/file.c
index 4724cc9ad650..63ec4a5bde77 100644
--- a/fs/fat/file.c
+++ b/fs/fat/file.c
@@ -519,4 +519,5 @@ 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/namei_msdos.c b/fs/fat/namei_msdos.c
index 582ca731a6c9..f157df4c1e51 100644
--- a/fs/fat/namei_msdos.c
+++ b/fs/fat/namei_msdos.c
@@ -641,6 +641,7 @@ 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 2649759c478a..3d24b44cb93d 100644
--- a/fs/fat/namei_vfat.c
+++ b/fs/fat/namei_vfat.c
@@ -1043,6 +1043,7 @@ 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)