linux-kernel - Re: [PATCHv2 1/7] block: check for valid bio while splitting

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Message-ID: <aJz9EUxTutWLxQmk@kbusch-mbp>
Date: Wed, 13 Aug 2025 15:01:05 -0600
From: Keith Busch <kbusch@...nel.org>
To: Bart Van Assche <bvanassche@....org>
Cc: Keith Busch <kbusch@...a.com>, linux-block@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	snitzer@...nel.org, axboe@...nel.dk, dw@...idwei.uk,
	brauner@...nel.org, Hannes Reinecke <hare@...e.de>
Subject: Re: [PATCHv2 1/7] block: check for valid bio while splitting

On Wed, Aug 13, 2025 at 01:41:49PM -0700, Bart Van Assche wrote:
> On 8/13/25 1:06 PM, Keith Busch wrote:
> > But I can't make that change because many scsi devices don't set the dma
> > alignment and get the default 511 value. This is fine for the memory
> > address offset, but the lengths sent for various inquriy commands are
> > much smaller, like 4 and 32 byte lengths. That length wouldn't pass the
> > dma alignment granularity, so I think the default value is far too
> > conservative. Does the address start size need to be a different limit
> > than minimum length? I feel like they should be the same, but maybe
> > that's just an nvme thing.
> 
> Hi Keith,
> 
> Maybe I misunderstood your question. It seems to me that the SCSI core
> sets the DMA alignment by default to four bytes. From
> drivers/scsi/hosts.c:

Thanks, I think you got my meaning. 

I'm using the AHCI driver. It looks like ata_scsi_dev_config() overrides
the dma_alignment to sector_size - 1, and that pattern goes way back,
almost 20 years ago, so maybe I can't change it.