linux-kernel - Re: [PATCH v2 02/12] scsi: mpt3sas: Make MPI2_CONFIG_PAGE_IO_UNIT

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Date:   Sun, 27 Aug 2023 00:05:42 -0700
From:   James Seo <james@...iv.tech>
To:     Kees Cook <keescook@...omium.org>
Cc:     Sathya Prakash <sathya.prakash@...adcom.com>,
        Sreekanth Reddy <sreekanth.reddy@...adcom.com>,
        Suganath Prabu Subramani 
        <suganath-prabu.subramani@...adcom.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        MPT-FusionLinux.pdl@...adcom.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 02/12] scsi: mpt3sas: Make
 MPI2_CONFIG_PAGE_IO_UNIT_8::Sensor[] a flexible array

On Fri, Aug 25, 2023 at 01:37:09PM -0700, Kees Cook wrote:
> On Sun, Aug 06, 2023 at 10:05:54AM -0700, James Seo wrote:
>>     Note that iounit_pg8 occurs in the middle of the per-adapter
>>     struct, not at the end. The per-adapter struct is extensively
> 
> This is especially bad/weird. Flex arrays aren't supposed to live there,
> so I think it'd be best to avoid this conversion (see below).
>
>>     used throughout mpt3sas even if its iounit_pg8 member isn't,
>>     resulting in an especially large amount of noise when comparing
>>     binary changes attributable to this commit.
> 
> Since the size reduction makes it hard to validate, how about just
> leaving it alone? Since nothing is using Sensor[], you could just make
> it a single instance:
> 
> -     MPI2_IOUNIT8_SENSOR
> -             Sensor[MPI2_IOUNITPAGE8_SENSOR_ENTRIES];/*0x10 */
> +     MPI2_IOUNIT8_SENSOR     Sensor;                 /*0x10 */
> 
> 
> or leave it as-is (i.e. drop this patch).
> 

I'd prefer not to paper it over by just up and pretending it's not a
flex array at all, but leaving things as-is feels like a waste, and I
understand the need to be conservative with storage drivers.

How do you feel about removing the struct containing the flex array
from the middle of the per-adapter struct, as per patch 8 in this
series? Moving that patch before this one in the ordering would
cleanly fix the misplaced flex array, but I imagine you'd be
especially keen on seeing Broadcom's approval for that one.

In any case, I'm fine with turning this into a single instance if it
comes down to it.