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Date:   Sun, 23 Jun 2019 21:53:26 -0600
From:   Andreas Dilger <adilger@...ger.ca>
To:     Deepa Dinamani <deepa.kernel@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Theodore Ts'o <tytso@....edu>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 08/16] ext4: Initialize timestamps limits

On Jun 18, 2019, at 8:31 AM, Deepa Dinamani <deepa.kernel@...il.com> 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@...il.com>
> Cc: "Theodore Ts'o" <tytso@....edu>

Reviewed-by: Andreas Dilger <adilger@...ger.ca>

> Cc: linux-ext4@...r.kernel.org
> ---
> 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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