linux-kernel - Re: [PATCH v11 24/26] virt: gunyah: Add irqfd interface

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Message-ID: <35e383da-2d4a-686d-5492-2ad3b8b4a039@linaro.org>
Date:   Tue, 18 Apr 2023 07:55:31 -0500
From:   Alex Elder <elder@...aro.org>
To:     Elliot Berman <quic_eberman@...cinc.com>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Prakruthi Deepak Heragu <quic_pheragu@...cinc.com>,
        Jonathan Corbet <corbet@....net>
Cc:     Murali Nalajala <quic_mnalajal@...cinc.com>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        Srivatsa Vaddagiri <quic_svaddagi@...cinc.com>,
        Carl van Schaik <quic_cvanscha@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        Will Deacon <will@...nel.org>, Andy Gross <agross@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Jassi Brar <jassisinghbrar@...il.com>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v11 24/26] virt: gunyah: Add irqfd interface

On 4/17/23 5:55 PM, Elliot Berman wrote:
>>>
>>> +struct gh_fn_irqfd_arg {
>>> +    __u32 fd;
>>
>> Should the "fd" field be signed?  Should it be an int?  (Perhaps
>> you're trying to define a fixed kernel API, so __s32 if signed would
>> be better.)
>>
> 
> It looked to me like some interfaces use __u32 and some use __s32. Is 
> one technically correct?

Good question.  It depends on how you use it.

It's a file descriptor, so it should be an int, and it appears
that's always a 32-bit signed (for 32 and 64 bit machines).
So the size seems to be right.

Whether it's signed or not I think depends on whether you
ever save an error value in this field.  I doubt you do,
but if you do, it should be signed.  Otherwise, the largest
value will never exceed INT_MAX/S32_MAX; and in that case
either is fine.

Will Gunyah ever run on a 32-bit machine?

					-Alex