linux-kernel - Re: [PATCH v2] exfat: do not clear VolumeDirty in writeback

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Date:   Thu, 17 Mar 2022 09:47:42 +0000
From:   "Kohada.Tetsuhiro@...MitsubishiElectric.co.jp" 
        <Kohada.Tetsuhiro@...MitsubishiElectric.co.jp>
To:     "Yuezhang.Mo@...y.com" <Yuezhang.Mo@...y.com>,
        Namjae Jeon <linkinjeon@...nel.org>
CC:     "sj1557.seo@...sung.com" <sj1557.seo@...sung.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Andy.Wu@...y.com" <Andy.Wu@...y.com>,
        "Wataru.Aoyama@...y.com" <Wataru.Aoyama@...y.com>
Subject: Re: [PATCH v2] exfat: do not clear VolumeDirty in writeback

Hi Yuezhang.Mo

> exfat_clear_volume_dirty() is only called in sync or umount context.
> In sync or umount context, all requests will be issued with REQ_SYNC regardless of whether REQ_SYNC is
> set when submitting buffer.
> 
> And since the request of set VolumeDirty is issued with REQ_SYNC. So for simplicity, call sync_dirty_buffer()
> unconditionally.

REQ_FUA and REQ_PREFLUSH may not make much sense on SD cards or USB sticks.
However, the behavior of SCSI/ATAPI type devices with lazy write cache is
 - Issue the SYNCHRONIZE_CACHE command to write all the data to the medium.
 - Issue a WRITE command with FORCE_UNIT_ACCESS (device does not use write cache) for the boot sector.
This guarantees a strict write order.

BR
T.Kohada