netdev - Re: [PATCH iproute2-next v2 1/6] ipaddress: Improve print

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Date:   Thu, 1 Feb 2018 12:59:17 +0200
From:   Serhey Popovych <serhe.popovych@...il.com>
To:     David Ahern <dsahern@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH iproute2-next v2 1/6] ipaddress: Improve print_linkinfo()

David Ahern wrote:
> On 1/30/18 11:09 AM, Serhey Popovych wrote:
> 
>> diff --git a/ip/ipaddress.c b/ip/ipaddress.c
>> index 051a05f..f8fd392 100644
>> --- a/ip/ipaddress.c
>> +++ b/ip/ipaddress.c
>> @@ -948,14 +948,14 @@ int print_linkinfo_brief(const struct sockaddr_nl *who,
>>  	parse_rtattr(tb, IFLA_MAX, IFLA_RTA(ifi), len);
>>  	if (tb[IFLA_IFNAME] == NULL) {
>>  		fprintf(stderr, "BUG: device with ifindex %d has nil ifname\n", ifi->ifi_index);
>> -		name = "<nil>";
>> +		name = ll_index_to_name(ifi->ifi_index);
> 
> This is one of those "should never happen checks" since the kernel
> always adds IFLA_IFNAME. Going to a cache to get a name for the index
> when the existing message is missing that attribute seems wrong. I
> realize the expectation is that the cache is empty today so if%d is
> returned, but that could change and it is the idea of consulting a cache
> that I think is wrong.
> 
> If that intention is to have a name I think it is safer to just have it
> set to if%d here (or in a helper that the cache also uses).

In my opinion in print_*() functions it is expected that cache isn't
empty. That's actually point where we benefit from cache.

I understand side effects this change may introduce and your concerns
about them. Will present small set of changes to export "if%d" template
from lib/ll_map.c for use here.

Using "<nil>" of something other, even for "should never happen" case
seems wrong to me.

> 
>>  	} else {
>>  		name = rta_getattr_str(tb[IFLA_IFNAME]);
>>  	}
>>  
>>  	if (pfilter->label &&
>>  	    (!pfilter->family || pfilter->family == AF_PACKET) &&
>> -	    fnmatch(pfilter->label, RTA_DATA(tb[IFLA_IFNAME]), 0))
>> +	    fnmatch(pfilter->label, name, 0))
>>  		return -1;
>>  
>>  	if (tb[IFLA_GROUP]) {
>> @@ -1057,6 +1057,7 @@ int print_linkinfo(const struct sockaddr_nl *who,
>>  	struct ifinfomsg *ifi = NLMSG_DATA(n);
>>  	struct rtattr *tb[IFLA_MAX+1];
>>  	int len = n->nlmsg_len;
>> +	const char *name;
>>  	unsigned int m_flag = 0;
>>  
>>  	if (n->nlmsg_type != RTM_NEWLINK && n->nlmsg_type != RTM_DELLINK)
>> @@ -1067,18 +1068,22 @@ int print_linkinfo(const struct sockaddr_nl *who,
>>  		return -1;
>>  
>>  	if (filter.ifindex && ifi->ifi_index != filter.ifindex)
>> -		return 0;
>> +		return -1;
>>  	if (filter.up && !(ifi->ifi_flags&IFF_UP))
>> -		return 0;
>> +		return -1;
>>  
>>  	parse_rtattr(tb, IFLA_MAX, IFLA_RTA(ifi), len);
>> -	if (tb[IFLA_IFNAME] == NULL)
>> +	if (tb[IFLA_IFNAME] == NULL) {
>>  		fprintf(stderr, "BUG: device with ifindex %d has nil ifname\n", ifi->ifi_index);
>> +		name = ll_index_to_name(ifi->ifi_index);
> 
> same here
> 
> 
>> +	} else {
>> +		name = rta_getattr_str(tb[IFLA_IFNAME]);
>> +	}
>>  
>>  	if (filter.label &&
>>  	    (!filter.family || filter.family == AF_PACKET) &&
>> -	    fnmatch(filter.label, RTA_DATA(tb[IFLA_IFNAME]), 0))
>> -		return 0;
>> +	    fnmatch(filter.label, name, 0))
>> +		return -1;
>>  
>>  	if (tb[IFLA_GROUP]) {
>>  		int group = rta_getattr_u32(tb[IFLA_GROUP]);
>> @@ -1105,16 +1110,7 @@ int print_linkinfo(const struct sockaddr_nl *who,
>>  		print_bool(PRINT_ANY, "deleted", "Deleted ", true);
>>  
>>  	print_int(PRINT_ANY, "ifindex", "%d: ", ifi->ifi_index);
>> -	if (tb[IFLA_IFNAME]) {
>> -		print_color_string(PRINT_ANY,
>> -				   COLOR_IFNAME,
>> -				   "ifname", "%s",
>> -				   rta_getattr_str(tb[IFLA_IFNAME]));
>> -	} else {
>> -		print_null(PRINT_JSON, "ifname", NULL, NULL);
>> -		print_color_null(PRINT_FP, COLOR_IFNAME,
>> -				 "ifname", "%s", "<nil>");
>> -	}
>> +	print_color_string(PRINT_ANY, COLOR_IFNAME, "ifname", "%s", name);
>>  
>>  	if (tb[IFLA_LINK]) {
>>  		int iflink = rta_getattr_u32(tb[IFLA_LINK]);
>>
> 




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