Re: [PATCH 03/14] scsi: core: Do not truncate INQUIRY data on modern devices

From: "Martin K. Petersen" <martin.petersen@oracle.com>
To: Bart Van Assche <bvanassche@acm.org>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>,
	linux-scsi@vger.kernel.org
Subject: Re: [PATCH 03/14] scsi: core: Do not truncate INQUIRY data on modern devices
Date: Thu, 03 Mar 2022 22:40:42 -0500	[thread overview]
Message-ID: <yq1mti6tmze.fsf@ca-mkp.ca.oracle.com> (raw)
In-Reply-To: <82c21426-4d23-1e5f-ef9b-212d623eb8f7@acm.org> (Bart Van Assche's message of "Wed, 2 Mar 2022 16:14:44 -0800")

Bart,

> Do the benefits of this change outweigh the additional complexity
> introduced by this code and the risk of breaking support for certain 
> devices? I'm asking this because the number of LLDs that sets
> inquiry_len is small:
>
> $ git grep -nH '>inquiry_len[[:blank:]]*=[[:blank:]]'|grep -v scsi_scan
> drivers/firewire/sbp2.c:1508:		sdev->inquiry_len = 36;
> drivers/staging/rts5208/rtsx.c:67:	sdev->inquiry_len = 36;
> drivers/usb/image/microtek.c:323:	s->inquiry_len = 0x24;
> drivers/usb/storage/scsiglue.c:77:	sdev->inquiry_len = 36;
>
> Does any of these LLDs support SPC-4 devices? Can this change
> e.g. break support for certain USB sticks?

The intent is to enable more modern protocol features on devices
attached using USB. I was concerned about blindly increasingly the
inquiry length and risk breaking older devices that we know are likely
to have problems in this department. At the same time the conservative
clamp on the inquiry length prevents several useful features from being
enabled on modern devices.

There is a risk associated with any change. This patch tries to strike a
reasonable balance between avoiding regressions and accommodating modern
USB SSDs.

-- 
Martin K. Petersen	Oracle Linux Engineering