linux-kernel - Re: [PATCH v3 1/3] scsi: Provide for avoiding trailing allocation length with VPD inquiries

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Message-ID: <a6a99a33-9124-bbc5-610b-a67d7af76c4a@gonehiking.org>
Date:   Tue, 4 Jan 2022 09:39:33 -0700
From:   Khalid Aziz and Shuah Khan <azizkhan@...ehiking.org>
To:     Christoph Hellwig <hch@....de>,
        "Maciej W. Rozycki" <macro@...am.me.uk>
Cc:     Khalid Aziz <khalid@...ehiking.org>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Nix <nix@...eri.org.uk>, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] scsi: Provide for avoiding trailing allocation
 length with VPD inquiries

On 1/3/22 01:23, Christoph Hellwig wrote:
> On Sun, Jan 02, 2022 at 11:23:45PM +0000, Maciej W. Rozycki wrote:
>> Allow SCSI hosts to request avoiding trailing allocation length with VPD
>> inquiries, and use the mechanism to work around an issue with at least
>> some BusLogic MultiMaster host bus adapters and observed with the BT-958
>> model specifically where issuing commands that return less data than
>> provided for causes fatal failures:
> Wouldn't it make more sesnse to hide this quirk insde of
> scsi_vpd_inquiry to also handle the scsi_get_vpd_buf case?  Something
> like:
>
>
> diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
> index 211aace69c22c..194a51f772aaa 100644
> --- a/drivers/scsi/scsi.c
> +++ b/drivers/scsi/scsi.c
> @@ -289,8 +289,8 @@ EXPORT_SYMBOL(scsi_track_queue_full);
>    *
>    * Returns size of the vpd page on success or a negative error number.
>    */
> -static int scsi_vpd_inquiry(struct scsi_device *sdev, unsigned char *buffer,
> -							u8 page, unsigned len)
> +static int __scsi_vpd_inquiry(struct scsi_device *sdev, unsigned char *buffer,
> +		u8 page, unsigned len)
>   {
>   	int result;
>   	unsigned char cmd[16];
> @@ -321,6 +321,20 @@ static int scsi_vpd_inquiry(struct scsi_device *sdev, unsigned char *buffer,
>   	return get_unaligned_be16(&buffer[2]) + 4;
>   }
>   
> +static int scsi_vpd_inquiry(struct scsi_device *sdev, unsigned char *buffer,
> +		u8 page, unsigned len)
> +{
> +	if (sdev->host->no_trailing_allocation_length) {
> +		int ret = __scsi_vpd_inquiry(sdev, buffer, page, min(4U, len));
> +
> +		if (ret < 4)
> +			return ret;
> +		len = min_t(unsigned int, ret, len);
> +	}
> +
> +	return __scsi_vpd_inquiry(sdev, buffer, page, len);
> +}
> +
>   /**
>    * scsi_get_vpd_page - Get Vital Product Data from a SCSI device
>    * @sdev: The device to ask

This is certainly better. It consolidates all the special cases for 
getting VPD pages in one location and ensures no cases are missed.

--
Khalid