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

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Date:   Mon, 02 Oct 2023 20:28:04 -0400
From:   "Martin K. Petersen" <martin.petersen@...cle.com>
To:     Bart Van Assche <bvanassche@....org>
Cc:     John Garry <john.g.garry@...cle.com>,
        Eric Biggers <ebiggers@...nel.org>, 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


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