linux-kernel - Re: [Xen-devel] [PATCH 5/6] xenbus: process be_watch events in xenwatch multithreading

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Date:   Fri, 14 Sep 2018 22:33:34 +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 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.
> 
>> +		p++;
>> +	}
>> +
>> +	return domid;
>> +}
>> +
>> +/* path: backend/<pvdev>/<domid>/... */
>> +static domid_t be_get_domid(struct xenbus_watch *watch,
>> +			    const char *path,
>> +			    const char *token)
>> +{
>> +	const char *p = path;
>> +
>> +	if (char_count(path, '/') < 2)
>> +		return 0;
>> +
>> +	p = strchr(p, '/') + 1;
>> +	p = strchr(p, '/') + 1;
> 
> Drop the call of char_count() above and test p for being non-NULL
> after each call of strchr?

The usage of char_count() is copied from xenbus_dev_changed() which is used to
process pattern 'backend/<type>/...'.

I use char_count() just because I would prefer we always use the same
equation/algorithm to process xenstore path in linux kernel.

I can drop it if it is better to not change char_count() from static to global
function.

556 void xenbus_dev_changed(const char *node, struct xen_bus_type *bus)
557 {
558         int exists, rootlen;
559         struct xenbus_device *dev;
560         char type[XEN_BUS_ID_SIZE];
561         const char *p, *root;
562
563         if (char_count(node, '/') < 2)
564                 return;
565
566         exists = xenbus_exists(XBT_NIL, node, "");
567         if (!exists) {
568                 xenbus_cleanup_devices(node, &bus->bus);
569                 return;
570         }
571
572         /* backend/<type>/... or device/<type>/... */
573         p = strchr(node, '/') + 1;
574         snprintf(type, XEN_BUS_ID_SIZE, "%.*s", (int)strcspn(p, "/"), p);
575         type[XEN_BUS_ID_SIZE-1] = '\0';

Dongli Zhang

> 
> 
> Juergen
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@...ts.xenproject.org
> https://lists.xenproject.org/mailman/listinfo/xen-devel
> 

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