linux-kernel - Re: [PATCH 03/21] fs/bdev: Add atomic write support info to statx

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Date:   Sun, 1 Oct 2023 06:23:31 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Eric Biggers <ebiggers@...nel.org>,
        John Garry <john.g.garry@...cle.com>
Cc:     axboe@...nel.dk, kbusch@...nel.org, hch@....de, sagi@...mberg.me,
        jejb@...ux.ibm.com, martin.petersen@...cle.com, djwong@...nel.org,
        viro@...iv.linux.org.uk, brauner@...nel.org,
        chandan.babu@...cle.com, dchinner@...hat.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
        linux-api@...r.kernel.org,
        Prasad Singamsetty <prasad.singamsetty@...cle.com>
Subject: Re: [PATCH 03/21] fs/bdev: Add atomic write support info to statx

On 9/29/23 15:49, Eric Biggers wrote:
> On Fri, Sep 29, 2023 at 10:27:08AM +0000, John Garry wrote:
>> diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
>> index 7cab2c65d3d7..c99d7cac2aa6 100644
>> --- a/include/uapi/linux/stat.h
>> +++ b/include/uapi/linux/stat.h
>> @@ -127,7 +127,10 @@ struct statx {
>>   	__u32	stx_dio_mem_align;	/* Memory buffer alignment for direct I/O */
>>   	__u32	stx_dio_offset_align;	/* File offset alignment for direct I/O */
>>   	/* 0xa0 */
>> -	__u64	__spare3[12];	/* Spare space for future expansion */
>> +	__u32	stx_atomic_write_unit_max;
>> +	__u32	stx_atomic_write_unit_min;
> 
> Maybe min first and then max?  That seems a bit more natural, and a lot of the
> code you've written handle them in that order.
> 
>> +#define STATX_ATTR_WRITE_ATOMIC		0x00400000 /* File supports atomic write operations */
> 
> How would this differ from stx_atomic_write_unit_min != 0?

Is it even possible that stx_atomic_write_unit_min == 0? My understanding
is that all Linux filesystems rely on the assumption that writing a single
logical block either succeeds or does not happen, even if a power failure
occurs between writing and reading a logical block.

Thanks,

Bart.