Re: [PATCH v5 4/7] PCI/sysfs: Allow userspace to query and set device reset mechanism

[Shanker R Donthineni <sdonthineni@nvidia.com>]

Hi Krzysztof,

On 6/6/21 7:58 AM, Krzysztof Wilczyński wrote:
> External email: Use caution opening links or attachments
>
>
> Hi Amey and Shanker,
>
> [...]
>> +static ssize_t reset_method_show(struct device *dev,
>> +                              struct device_attribute *attr,
>> +                              char *buf)
>> +{
>> +     struct pci_dev *pdev = to_pci_dev(dev);
>> +     ssize_t len = 0;
>> +     int i, prio;
>> +
>> +     for (prio = PCI_RESET_METHODS_NUM; prio; prio--) {
>> +             for (i = 0; i < PCI_RESET_METHODS_NUM; i++) {
>> +                     if (prio == pdev->reset_methods[i]) {
>> +                             len += sysfs_emit_at(buf, len, "%s%s",
>> +                                                  len ? "," : "",
>> +                                                  pci_reset_fn_methods[i].name);
>> +                             break;
>> +                     }
>> +             }
>> +
>> +             if (i == PCI_RESET_METHODS_NUM)
>> +                     break;
>> +     }
>> +
>> +     return len;
>> +}
> Make sure to include trailing newline when exposing values through the
> sysfs object to the userspace in the above show() function.

Agree new line is needed. Will fix it.
> [...]
>> +static ssize_t reset_method_store(struct device *dev,
>> +                               struct device_attribute *attr,
>> +                               const char *buf, size_t count)
> [...]
>> +
>> +     while ((name = strsep((char **)&buf, ",")) != NULL) {
> [...]
>
> This is something that I wonder could benefit from the following:
>
>   char *options, *end;
>
>   if (count >= (PAGE_SIZE - 1))
>         return -EINVAL;
>
>   options = kstrndup(buf, count, GFP_KERNEL);
>   if (!options)
>         return -ENOMEM;
>
>   while ((name = strsep(&options, ",")) != NULL) {
>         ...
>   }
>
>   ...
>
>   kfree(options);
>
> Why?  To avoid changing the string buffer that has been passed to
> reset_method_store() as strsep() while parsing will update the content
> of the buffer.  The cast to (char **), aside of most definitely allowing
> to suppress the probable compiler warning, will also allow for what
> should be a technically a constant string (to which we got a pointer to)
> to be modified.  I am not sure how much could this be of a problem, but
> I would try not to do it, if possible.

Thanks, will use temporary buffer for parsing string.
>
> [...]
>> +set_reset_methods:
>> +     memcpy(pdev->reset_methods, reset_methods, sizeof(reset_methods));
>> +     return count;
>> +}
>> +
>> +static DEVICE_ATTR_RW(reset_method);
> A small nitpikc: customary there is no space (a newline) between the
> function and the macro, the macro follows immediately after.

Will fix it.
>         Krzysztof