On Jun 18, 2019, at 8:31 AM, Deepa Dinamani <deepa.kernel@xxxxxxxxx> wrote:
>
> 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
> a4dad1ae24f85i(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.
>
> Signed-off-by: Deepa Dinamani <deepa.kernel@xxxxxxxxx>
> Cc: "Theodore Ts'o" <tytso@xxxxxxx>
Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx>
> Cc: linux-ext4@xxxxxxxxxxxxxxx
> ---
> fs/ext4/ext4.h | 4 ++++
> fs/ext4/super.c | 16 ++++++++++++++--
> 2 files changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 1cb67859e051..3f13cf12ae7f 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1631,6 +1631,10 @@ 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
> */
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 4079605d437a..0357acdeb6d3 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -4035,8 +4035,20 @@ 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 spaces 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 = 0;
> + 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);
> --
> 2.17.1
>
Cheers, Andreas
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