linux-kernel - Re: [PATCH 4/5] iommu: Regulate errno in ->attach

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Message-ID: <YyGaqsXSDMn8R12R@nvidia.com>
Date:   Wed, 14 Sep 2022 06:11:06 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>
Cc:     Nicolin Chen <nicolinc@...dia.com>, joro@...tes.org,
        suravee.suthikulpanit@....com, will@...nel.org,
        robin.murphy@....com, robdclark@...il.com, dwmw2@...radead.org,
        baolu.lu@...ux.intel.com, agross@...nel.org,
        bjorn.andersson@...aro.org, konrad.dybcio@...ainline.org,
        matthias.bgg@...il.com, heiko@...ech.de, orsonzhai@...il.com,
        baolin.wang@...ux.alibaba.com, zhang.lyra@...il.com,
        thierry.reding@...il.com, sricharan@...eaurora.org,
        yong.wu@...iatek.com, vdumpa@...dia.com, jonathanh@...dia.com,
        tglx@...utronix.de, shameerali.kolothum.thodi@...wei.com,
        thunder.leizhen@...wei.com, christophe.jaillet@...adoo.fr,
        yangyingliang@...wei.com, jon@...id-run.com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-tegra@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 4/5] iommu: Regulate errno in ->attach_dev callback
 functions

On Tue, Sep 13, 2022 at 01:27:03PM +0100, Jean-Philippe Brucker wrote:
> I think in the future it will be too easy to forget about the constrained
> return value of attach() while modifying some other part of the driver,
> and let an external helper return EINVAL. So I'd rather not propagate ret
> from outside of viommu_domain_attach() and finalise().

Fortunately, if -EINVAL is wrongly returned it only creates an
inefficiency, not a functional problem. So we do not need to be
precise here.

> Since we can't guarantee that APIs like virtio or ida won't ever return
> EINVAL, we should set all return values:

I dislike this alot, it squashes all return codes to try to optimize
an obscure failure path :(

Jason