Subject: Re: Resource usages in Linux drivers

From: Sergei Shtylyov <[email-masked]>
Date: Thu, 23 Apr 2015 13:37:04 +0300

On 4/23/2015 1:08 PM, Jia-Ju Bai wrote:

>>>> I am very sorry to trouble you.

>>>> I find that resource management is error-prone when writing Linux drivers,
>>>> and
>>>> many problems may occur, such as resource leaks.
>>>> Meanwhile, I find that many applied patches in the kernel mailing list focus
>>>> on releasing allocated resources, especially in error-handling paths.

>>>> Therefore, I have a question: is it possible to automatically release
>>>> allocated resources in drivers before unloading and in error-handling paths?

>>>    Yes, there's managed device API, look for functions starting with devm_.
>>> There's one limitation though: it can be used only in the driver's probe()
>>> method, so can't be used when e.g. network device is being opened.

>> I think many APIs, such as kmalloc, can also be managed like garbage
>> collection in Java.
>> Maybe the performance is a matter.

>>>> I am looking forward to your reply, thanks!

>>>    Such questions should actually be asked on the mailing lists, not
>>> personally.

>> I am sorry for that, and I will cc to the mailing lists and other maintainers.

> I find that some common APIs are not managed, such as napi_enable and
> napi_start_queue. Is it possible to provide managed APIs for them?

    No, they're only called from ndo_open() method IIRC. The device managed 
APIs can only be called at the device probing time.

> I also find many drivers do not use these managed APIs, especially in ethernet
> card drivers (like e100, r8169). Is it possible to change them?

    Patches welcome. :-)

> Best wishes,
> Jia-Ju Bai

WBR, Sergei