linux-kernel - Re: [PATCH v2 3/5] soc: qcom: smem: Support global partition

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Date:   Wed, 4 Oct 2017 21:15:23 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Chris Lew <clew@...eaurora.org>
Cc:     andy.gross@...aro.org, david.brown@...aro.org,
        aneela@...eaurora.org, linux-arm-msm@...r.kernel.org,
        linux-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/5] soc: qcom: smem: Support global partition

On Fri 15 Sep 14:02 PDT 2017, Chris Lew wrote:

> 
> 
> On 9/15/2017 11:33 AM, Bjorn Andersson wrote:
> > On Thu 14 Sep 14:25 PDT 2017, Chris Lew wrote:
> > 
> > [..]
> > > +static struct smem_ptable *qcom_smem_get_ptable(struct qcom_smem *smem)
> > >   {
> > > -	struct smem_partition_header *header;
> > > -	struct smem_ptable_entry *entry;
> > >   	struct smem_ptable *ptable;
> > > -	unsigned remote_host;
> > > -	u32 version, host0, host1;
> > > -	int i;
> > > +	u32 version;
> > >   	ptable = smem->regions[0].virt_base + smem->regions[0].size - SZ_4K;
> > >   	if (memcmp(ptable->magic, SMEM_PTABLE_MAGIC, sizeof(ptable->magic)))
> > > -		return 0;
> > > +		return NULL;
> > >   	version = le32_to_cpu(ptable->version);
> > >   	if (version != 1) {
> > >   		dev_err(smem->dev,
> > >   			"Unsupported partition header version %d\n", version);
> > > +		return ERR_PTR(-EINVAL);
> > 
> > In the calling places NULL and -EINVAL are both treated as -EINVAL, so I
> > think it's better to just return NULL here as well as check for !ptable
> > in callers.
> > 
> > Regards,
> > Bjorn
> > 
> 
> qcom_smem_enumerate_partitions allowed the partition table to be optional
> before. I want to keep that behavior for V11 where smem might only have the
> global heap. The probe will continue with a NULL/0 return from
> qcom_get_ptable/qcom_smem_enumerate_partitions.
> 

You're right, I missed that detail.

Which allows me to argue that I do not feel that testing with
IS_ERR_OR_NULL() to let a 0 pass through to the caller is not obvious.

I think it's better if you replace the NULL with ERR_PTR(-ENOENT), which
you test and forward in both callers and then for the one caller where
partitions are optional you check if ret < 0 && ret != -ENOENT.

(Alternatively you check for NULL in enumerate_partitions() and return 0
with a nice comment saying that everything is okay)

Regards,
Bjorn