ext4: Initialize timestamps limits

ext4 has different overflow limits for max filesystem
timestamps based on the extra bytes available.

The timestamp limits are calculated according to the
encoding table in
a4dad1aei(ext4: Fix handling of extended tv_sec):

* extra  msb of                         adjust for signed
* epoch  32-bit                         32-bit tv_sec to
* bits   time    decoded 64-bit tv_sec  64-bit tv_sec      valid time range
* 0 0    1    -0x80000000..-0x00000001  0x000000000   1901-12-13..1969-12-31
* 0 0    0    0x000000000..0x07fffffff  0x000000000   1970-01-01..2038-01-19
* 0 1    1    0x080000000..0x0ffffffff  0x100000000   2038-01-19..2106-02-07
* 0 1    0    0x100000000..0x17fffffff  0x100000000   2106-02-07..2174-02-25
* 1 0    1    0x180000000..0x1ffffffff  0x200000000   2174-02-25..2242-03-16
* 1 0    0    0x200000000..0x27fffffff  0x200000000   2242-03-16..2310-04-04
* 1 1    1    0x280000000..0x2ffffffff  0x300000000   2310-04-04..2378-04-22
* 1 1    0    0x300000000..0x37fffffff  0x300000000   2378-04-22..2446-05-10

Note that the time limits are not correct for deletion times.

Added a warn when an inode cannot be extended to incorporate an
extended timestamp.
Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Acked-by: Jeff Layton <jlayton@kernel.org>
Cc: tytso@mit.edu
Cc: adilger.kernel@dilger.ca
Cc: linux-ext4@vger.kernel.org

fs/ext4/ext4.h

@@ -828,11 +828,15 @@ static inline void ext4_decode_extra_time(struct timespec64 *time,
 
 #define EXT4_INODE_SET_XTIME(xtime, inode, raw_inode)				\
 do {										\
-	(raw_inode)->xtime = cpu_to_le32((inode)->xtime.tv_sec);		\
 	if (EXT4_FITS_IN_INODE(raw_inode, EXT4_I(inode), xtime ## _extra))     {\
+		(raw_inode)->xtime = cpu_to_le32((inode)->xtime.tv_sec);	\
 		(raw_inode)->xtime ## _extra =					\
 				ext4_encode_extra_time(&(inode)->xtime);	\
 		}								\
+	else	{\
+		(raw_inode)->xtime = cpu_to_le32(clamp_t(int32_t, (inode)->xtime.tv_sec, S32_MIN, S32_MAX));	\
+		ext4_warning_inode(inode, "inode does not support timestamps beyond 2038"); \
+	} \
 } while (0)
 
 #define EXT4_EINODE_SET_XTIME(xtime, einode, raw_inode)			       \
@@ -1632,6 +1636,10 @@ static inline void ext4_clear_state_flags(struct ext4_inode_info *ei)
 
 #define EXT4_GOOD_OLD_INODE_SIZE 128
 
+#define EXT4_EXTRA_TIMESTAMP_MAX	(((s64)1 << 34) - 1  + S32_MIN)
+#define EXT4_NON_EXTRA_TIMESTAMP_MAX	S32_MAX
+#define EXT4_TIMESTAMP_MIN		S32_MIN
+
 /*
  * Feature set definitions
  */

fs/ext4/super.c

@@ -4035,8 +4035,21 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 			       sbi->s_inode_size);
 			goto failed_mount;
 		}
-		if (sbi->s_inode_size > EXT4_GOOD_OLD_INODE_SIZE)
-			sb->s_time_gran = 1 << (EXT4_EPOCH_BITS - 2);
+		/*
+		 * i_atime_extra is the last extra field available for [acm]times in
+		 * struct ext4_inode. Checking for that field should suffice to ensure
+		 * we have extra space for all three.
+		 */
+		if (sbi->s_inode_size >= offsetof(struct ext4_inode, i_atime_extra) +
+			sizeof(((struct ext4_inode *)0)->i_atime_extra)) {
+			sb->s_time_gran = 1;
+			sb->s_time_max = EXT4_EXTRA_TIMESTAMP_MAX;
+		} else {
+			sb->s_time_gran = NSEC_PER_SEC;
+			sb->s_time_max = EXT4_NON_EXTRA_TIMESTAMP_MAX;
+		}
+
+		sb->s_time_min = EXT4_TIMESTAMP_MIN;
 	}
 
 	sbi->s_desc_size = le16_to_cpu(es->s_desc_size);