netdev - Re: [PATCH v2 4/4] wcn36xx: Add debugfs entry to read firmware feature strings

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Date:   Wed, 27 Jul 2022 14:08:30 +0300
From:   Kalle Valo <kvalo@...nel.org>
To:     Bryan O'Donoghue <bryan.odonoghue@...aro.org>
Cc:     loic.poulain@...aro.org, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, wcn36xx@...ts.infradead.org,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2 4/4] wcn36xx: Add debugfs entry to read firmware feature strings

Bryan O'Donoghue <bryan.odonoghue@...aro.org> writes:

> On 27/07/2022 11:31, Kalle Valo wrote:
>> Bryan O'Donoghue <bryan.odonoghue@...aro.org> writes:
>
>>> +static ssize_t read_file_firmware_feature_caps(struct file *file,
>>> +					       char __user *user_buf,
>>> +					       size_t count, loff_t *ppos)
>>> +{
>>> +	struct wcn36xx *wcn = file->private_data;
>>> +	unsigned long page = get_zeroed_page(GFP_KERNEL);
>>> +	char *p = (char *)page;
>>> +	int i;
>>> +	int ret;
>>> +
>>> +	if (!p)
>>> +		return -ENOMEM;
>>> +
>>> +	mutex_lock(&wcn->hal_mutex);
>>> +	for (i = 0; i < MAX_FEATURE_SUPPORTED; i++) {
>>> +		if (wcn36xx_firmware_get_feat_caps(wcn->fw_feat_caps, i)) {
>>> +			p += sprintf(p, "%s\n",
>>> +				     wcn36xx_firmware_get_cap_name(i));
>>> +		}
>>> +	}
>>> +	mutex_unlock(&wcn->hal_mutex);
>>> +
>>> +	ret = simple_read_from_buffer(user_buf, count, ppos, (char *)page,
>>> +				      (unsigned long)p - page);
>>> +
>>> +	free_page(page);
>>> +	return ret;
>>> +}
>>
>> Why not use the normal use kzalloc() and kfree()? That way you would not
>> need a separate page variable. What's the benefit from
>> get_zeroed_page()?
>
>
> TBH I did a copy/paste here from another driver... I forget which
>>
>> Also I don't see any checks for a memory allocation failure.
>>
>
> its there
>
> char *p = (char*) page;
>
> if (!p)
>     return -ENOMEM;

Ah, it's pretty evil to have the error handling so far away from the
actual call :)

> I can V2 this for kzalloc and kfree if you prefer though

Yes, please do that. We should use standard infrastructure as much as
possible.

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