On Apr 16, 2019, at 8:34 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>
> Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx>
> Cc: linux-ext4@xxxxxxxxxxxxxxx
Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx>
> #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 f5b828bf1299..3a63a23219a8 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3930,8 +3930,20 @@ 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.
There was never a time when only i_ctime_extra or i_mtime_extra was present in the
inode, so this should be totally safe. The code may check for them independently
for correctness reasons (e.g. in case of some corruption of the on-disk inode or
whatever), but for a global state like this it is totally safe to check all three
of the fields based on the presence of i_atime_extra.
> + */
> + 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
Attachment:
signature.asc
Description: Message signed with OpenPGP
