fat: add functions to update and truncate timestamps appropriately

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.

Link: http://lkml.kernel.org/r/38af1ba3c3cf0d7381ce7b63077ef8af75901532.1538363961.git.sorenson@redhat.com
Signed-off-by: Frank Sorenson <sorenson@redhat.com>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

6 files changed, 87 insertions, 0 deletions

diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index 9d7d2d5da28b..4e1b2f6df5e6 100644
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -416,6 +416,10 @@ 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..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;
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)