linux-kernel - Re: [PATCH v2 09/24] quota: avoid time_t in v1_disk

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Message-ID: <20191216131419.GG22157@quack2.suse.cz>
Date:   Mon, 16 Dec 2019 14:14:19 +0100
From:   Jan Kara <jack@...e.cz>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     y2038@...ts.linaro.org, linux-kernel@...r.kernel.org,
        Jan Kara <jack@...e.com>
Subject: Re: [PATCH v2 09/24] quota: avoid time_t in v1_disk_dqblk definition

On Fri 13-12-19 21:52:14, Arnd Bergmann wrote:
> The time_t type is part of the user interface and not always the
> same, with the move to 64-bit timestamps and the difference between
> architectures.
> 
> Make the quota format definition independent of this type and use
> a basic type of the same length. Make it unsigned in the process
> to keep the v1 format working until year 2106 instead of 2038
> on 32-bit architectures.
> 
> Hopefully, everybody has already moved to a newer format long
> ago (v2 was introduced with linux-2.4), but it's hard to be sure.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

What's worse, time_t is actually a part of on-disk format for this ancient
quota format making format incompatible between 32-bit and 64-bit
systems... Anyway, your patch looks good, I'll add it to my tree (speak up
if you want to merge it yourself due to something depending on it).

								Honza

> ---
>  fs/quota/quotaio_v1.h | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/quota/quotaio_v1.h b/fs/quota/quotaio_v1.h
> index bd11e2c08119..31dca9a89176 100644
> --- a/fs/quota/quotaio_v1.h
> +++ b/fs/quota/quotaio_v1.h
> @@ -25,8 +25,10 @@ struct v1_disk_dqblk {
>  	__u32 dqb_ihardlimit;	/* absolute limit on allocated inodes */
>  	__u32 dqb_isoftlimit;	/* preferred inode limit */
>  	__u32 dqb_curinodes;	/* current # allocated inodes */
> -	time_t dqb_btime;	/* time limit for excessive disk use */
> -	time_t dqb_itime;	/* time limit for excessive inode use */
> +
> +	/* below fields differ in length on 32-bit vs 64-bit architectures */
> +	unsigned long dqb_btime; /* time limit for excessive disk use */
> +	unsigned long dqb_itime; /* time limit for excessive inode use */
>  };
>  
>  #define v1_dqoff(UID)      ((loff_t)((UID) * sizeof (struct v1_disk_dqblk)))
> -- 
> 2.20.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR