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To:     Bart Van Assche <bvanassche@acm.org>
Cc:     John Garry <john.g.garry@oracle.com>,
        Eric Biggers <ebiggers@kernel.org>, axboe@kernel.dk,
        kbusch@kernel.org, hch@lst.de, sagi@grimberg.me,
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        Prasad Singamsetty <prasad.singamsetty@oracle.com>
Subject: Re: [PATCH 03/21] fs/bdev: Add atomic write support info to statx
From:   "Martin K. Petersen" <martin.petersen@oracle.com>
Organization: Oracle Corporation
Message-ID: <yq1r0mctv2d.fsf@ca-mkp.ca.oracle.com>
References: <20230929102726.2985188-1-john.g.garry@oracle.com>
        <20230929102726.2985188-4-john.g.garry@oracle.com>
        <20230929224922.GB11839@google.com>
        <b9c266d2-d5d6-4294-9a95-764641e295b4@acm.org>
        <d3a8b9b0-b24c-a002-e77d-56380ee785a5@oracle.com>
        <2c929105-7c7f-43c5-a105-42d1813d0e29@acm.org>
Date:   Mon, 02 Oct 2023 20:28:04 -0400
In-Reply-To: <2c929105-7c7f-43c5-a105-42d1813d0e29@acm.org> (Bart Van Assche's
        message of "Mon, 2 Oct 2023 11:39:00 -0700")
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Bart,

> Neither the SCSI SBC standard nor the NVMe standard defines a "minimum
> atomic write unit". So why to introduce something in the Linux kernel
> that is not defined in common storage standards?

From SBC-5:

"The ATOMIC TRANSFER LENGTH GRANULARITY field indicates the minimum
transfer length for an atomic write command."

> I propose to leave out stx_atomic_write_unit_min from
> struct statx and also to leave out atomic_write_unit_min_sectors from
> struct queue_limits. My opinion is that we should not support block
> devices in the Linux kernel that do not write logical blocks atomically.

The statx values exist to describe the limits for I/Os sent using
RWF_ATOMIC and IOCB_ATOMIC. These limits may be different from other
reported values such as the filesystem block size and the logical block
size of the underlying device.

-- 
Martin K. Petersen	Oracle Linux Engineering