linux-kernel - Re: [PATCH][next] qed/qed_ll2: Replace one-element array with flexible-array member

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Message-ID: <20200929131915.GC28922@embeddedor>
Date:   Tue, 29 Sep 2020 08:19:15 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     David Miller <davem@...emloft.net>
Cc:     aelior@...vell.com, kuba@...nel.org,
        GR-everest-linux-l2@...vell.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, keescook@...omium.org
Subject: Re: [PATCH][next] qed/qed_ll2: Replace one-element array with
 flexible-array member

On Mon, Sep 28, 2020 at 06:48:14PM -0700, David Miller wrote:
> From: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> Date: Mon, 28 Sep 2020 10:16:17 -0500
> 
> > There is a regular need in the kernel to provide a way to declare having
> > a dynamically sized set of trailing elements in a structure. Kernel code
> > should always use “flexible array members”[1] for these cases. The older
> > style of one-element or zero-length arrays should no longer be used[2].
> > 
> > Refactor the code according to the use of a flexible-array member in
> > struct qed_ll2_tx_packet, instead of a one-element array and use the
> > struct_size() helper to calculate the size for the allocations. Commit
> > f5823fe6897c ("qed: Add ll2 option to limit the number of bds per packet")
> > was used as a reference point for these changes.
> > 
> > Also, it's important to notice that flexible-array members should occur
> > last in any structure, and structures containing such arrays and that
> > are members of other structures, must also occur last in the containing
> > structure. That's why _cur_completing_packet_ is now moved to the bottom
> > in struct qed_ll2_tx_queue. _descq_mem_ and _cur_send_packet_ are also
> > moved for unification.
> > 
> > [1] https://en.wikipedia.org/wiki/Flexible_array_member
> > [2] https://www.kernel.org/doc/html/v5.9-rc1/process/deprecated.html#zero-length-and-one-element-arrays
> > 
> > Tested-by: kernel test robot <lkp@...el.com>
> 
> I find such tags enormously misleading, because the kernel test robot
> didn't perform any functional testing of this change and honestly
> that's the part I'm more concerned about rather than "does it build".
> 
> Anyone can check test the build.
> 

I agree.  I should add a Built-Tested-by tag instead next time.

> > Link: https://lore.kernel.org/lkml/5f707198.PA1UCZ8MYozYZYAR%25lkp@intel.com/
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> 
> Applied.

Thanks
--
Gustavo