linux-kernel - Re: [PATCH 6/8] bsg-lib: handle bidi requests without block layer help

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Message-ID: <20181114154857.GA28985@lst.de>
Date:   Wed, 14 Nov 2018 16:48:57 +0100
From:   Christoph Hellwig <hch@....de>
To:     Benjamin Block <bblock@...ux.ibm.com>
Cc:     Christoph Hellwig <hch@....de>, axboe@...nel.dk,
        martin.petersen@...cle.com, ooo@...ctrozaur.com,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Benjamin Block <bblock@...ux.vnet.ibm.com>,
        linux-scsi@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/8] bsg-lib: handle bidi requests without block layer
 help

On Tue, Nov 13, 2018 at 03:35:20PM +0100, Benjamin Block wrote:
> This seems like a non-obvious user-breakage. So apart from removing the
> in-kernel stuff that uses bidirectional commands you also forbid
> userspace from every using them? That seems wrong to me.
> 
> There is other SCSI Command Sets than OSD that provide bidirectional
> commands, even SBC has some (i.e.  X*WRITE*, COMPARE AND WRITE).

Yes, there are a few.  But the only driver that even supports them
right now is iscsi_tcp to start with, and we have to drag a significant
amount of code around just to support this corner case.