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Message-ID: <b9c266d2-d5d6-4294-9a95-764641e295b4@acm.org>
Date:   Sun, 1 Oct 2023 06:23:31 -0700
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Subject: Re: [PATCH 03/21] fs/bdev: Add atomic write support info to statx
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To:     Eric Biggers <ebiggers@kernel.org>,
        John Garry <john.g.garry@oracle.com>
Cc:     axboe@kernel.dk, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me,
        jejb@linux.ibm.com, martin.petersen@oracle.com, djwong@kernel.org,
        viro@zeniv.linux.org.uk, brauner@kernel.org,
        chandan.babu@oracle.com, dchinner@redhat.com,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-nvme@lists.infradead.org, linux-xfs@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, tytso@mit.edu, jbongio@google.com,
        linux-api@vger.kernel.org,
        Prasad Singamsetty <prasad.singamsetty@oracle.com>
References: <20230929102726.2985188-1-john.g.garry@oracle.com>
 <20230929102726.2985188-4-john.g.garry@oracle.com>
 <20230929224922.GB11839@google.com>
From:   Bart Van Assche <bvanassche@acm.org>
In-Reply-To: <20230929224922.GB11839@google.com>
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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.