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From:   Andreas Dilger <adilger@dilger.ca>
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Subject: Re: [PATCH 08/16] ext4: Initialize timestamps limits
Date:   Sun, 23 Jun 2019 21:53:26 -0600
In-Reply-To: <20190618143110.6720-8-deepa.kernel@gmail.com>
Cc:     Arnd Bergmann <arnd@arndb.de>, Theodore Ts'o <tytso@mit.edu>,
        Ext4 Developers List <linux-ext4@vger.kernel.org>
To:     Deepa Dinamani <deepa.kernel@gmail.com>
References: <20190618143110.6720-1-deepa.kernel@gmail.com>
 <20190618143110.6720-8-deepa.kernel@gmail.com>
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On Jun 18, 2019, at 8:31 AM, Deepa Dinamani <deepa.kernel@gmail.com> =
wrote:
>=20
> ext4 has different overflow limits for max filesystem
> timestamps based on the extra bytes available.
>=20
> The timestamp limits are calculated according to the
> encoding table in
> a4dad1ae24f85i(ext4: Fix handling of extended tv_sec):
>=20
> * 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
>=20
> Note that the time limits are not correct for deletion times.
>=20
> Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
> Cc: "Theodore Ts'o" <tytso@mit.edu>

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

> Cc: linux-ext4@vger.kernel.org
> ---
> fs/ext4/ext4.h  |  4 ++++
> fs/ext4/super.c | 16 ++++++++++++++--
> 2 files changed, 18 insertions(+), 2 deletions(-)
>=20
> 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)
>=20
> #define EXT4_GOOD_OLD_INODE_SIZE 128
>=20
> +#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 =3D 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 >=3D offsetof(struct ext4_inode, =
i_atime_extra) +
> +			sizeof(((struct ext4_inode *)0)->i_atime_extra)) =
{
> +			sb->s_time_gran =3D 1;
> +			sb->s_time_max =3D EXT4_EXTRA_TIMESTAMP_MAX;
> +		} else {
> +			sb->s_time_gran =3D 0;
> +			sb->s_time_max =3D EXT4_NON_EXTRA_TIMESTAMP_MAX;
> +		}
> +
> +		sb->s_time_min =3D EXT4_TIMESTAMP_MIN;
> 	}
>=20
> 	sbi->s_desc_size =3D le16_to_cpu(es->s_desc_size);
> --
> 2.17.1
>=20


Cheers, Andreas


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