linux-kernel - Re: [Xen-devel] [PATCH 5/6] xenbus: process be

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Date:   Fri, 14 Sep 2018 22:29:58 +0800
From:   Dongli Zhang <dongli.zhang@...cle.com>
To:     Juergen Gross <jgross@...e.com>, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org
Cc:     wei.liu2@...rix.com, konrad.wilk@...cle.com,
        srinivas.eeda@...cle.com, paul.durrant@...rix.com,
        boris.ostrovsky@...cle.com, roger.pau@...rix.com
Subject: Re: [Xen-devel] [PATCH 5/6] xenbus: process be_watch events in
 xenwatch multithreading

Hi Juergen,

On 09/14/2018 10:26 PM, Juergen Gross wrote:
> On 14/09/18 16:18, Dongli Zhang wrote:
>> Hi Juergen,
>>
>> On 09/14/2018 05:12 PM, Juergen Gross wrote:
>>> On 14/09/18 09:34, Dongli Zhang wrote:
>>>> This is the 5th patch of a (6-patch) patch set.
>>>>
>>>> With this patch, watch event in relative path pattern
>>>> 'backend/<pvdev>/<domid>i/...' can be processed in per-domU xenwatch
>>>
>>> superfluous "i" ----------^
>>>
>>>> thread.
>>>>
>>>> Signed-off-by: Dongli Zhang <dongli.zhang@...cle.com>
>>>> ---
>>>>  drivers/xen/xenbus/xenbus_probe.c         |  2 +-
>>>>  drivers/xen/xenbus/xenbus_probe_backend.c | 32 +++++++++++++++++++++++++++++++
>>>>  include/xen/xenbus.h                      |  2 ++
>>>>  3 files changed, 35 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
>>>> index ba0644c..aa1b15a 100644
>>>> --- a/drivers/xen/xenbus/xenbus_probe.c
>>>> +++ b/drivers/xen/xenbus/xenbus_probe.c
>>>> @@ -552,7 +552,7 @@ int xenbus_probe_devices(struct xen_bus_type *bus)
>>>>  }
>>>>  EXPORT_SYMBOL_GPL(xenbus_probe_devices);
>>>>  
>>>> -static unsigned int char_count(const char *str, char c)
>>>> +unsigned int char_count(const char *str, char c)
>>>
>>> Please change the name of the function when making it globally
>>> visible, e.g. by prefixing "xenbus_".
>>>
>>> Generally I think you don't need to use it below.
>>>
>>>>  {
>>>>  	unsigned int i, ret = 0;
>>>>  
>>>> diff --git a/drivers/xen/xenbus/xenbus_probe_backend.c b/drivers/xen/xenbus/xenbus_probe_backend.c
>>>> index b0bed4f..50df86a 100644
>>>> --- a/drivers/xen/xenbus/xenbus_probe_backend.c
>>>> +++ b/drivers/xen/xenbus/xenbus_probe_backend.c
>>>> @@ -211,9 +211,41 @@ static void backend_changed(struct xenbus_watch *watch,
>>>>  	xenbus_dev_changed(path, &xenbus_backend);
>>>>  }
>>>>  
>>>> +static domid_t path_to_domid(const char *path)
>>>> +{
>>>> +	const char *p = path;
>>>> +	domid_t domid = 0;
>>>> +
>>>> +	while (*p) {
>>>> +		if (*p < '0' || *p > '9')
>>>> +			break;
>>>> +		domid = (domid << 3) + (domid << 1) + (*p - '0');
>>>
>>> reinventing atoi()?
>>>
>>> Please don't do that. kstrtou16() seems to be a perfect fit.
>>
>> I did use kstrtou*() in the early prototype and realized kstrtou16() returns 0
>> if the input string contains non-numerical characters.
>>
>> E.g., the example of input can be "1/0/state", where 1 is fotherend_id
>> (frontend_id) and 0 is handle.
>>
>> When "1/0/state" is used at input, kstrtou16() returns 0 (returned integer) and
>> -22 (error).
> 
> Aah, okay. Then simple_strtoul()?

I did consider simple_strtoul() initially. Unfortunately, it is obsolete (below
line 81). AFAIR, the patch would not be able to pass the check_patch script when
this function is used.

  75 /**
  76  * simple_strtoul - convert a string to an unsigned long
  77  * @cp: The start of the string
  78  * @endp: A pointer to the end of the parsed string will be placed here
  79  * @base: The number base to use
  80  *
  81  * This function is obsolete. Please use kstrtoul instead.
  82  */
  83 unsigned long simple_strtoul(const char *cp, char **endp, unsigned int base)
  84 {
  85         return simple_strtoull(cp, endp, base);
  86 }

Dongli Zhang

> 
> 
> Juergen
>