Re: [LARTC] a question about q_tbf.c of TC

[Martin Devera <devik@cdi.cz>]

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Hello,

IIRC it is ok. The TCA_KIND is used as upper level ID. TCA_TBF_PARAMS
is in second level, it is contained as data of TBF kind. Take dump
of whole NL message and study carefully.
It is like:
TCA_KIND  "TBF"
TCA_XXXX {
  TCA_TBF_PARAMS ....
  TCA_TBF_XXXX .....
}
TCA_YYY ...

So that when rtnetlink_rev_msg parses message first time it skips
all occurences of TCA_TBF_*. q_tbf is given data part of TCA_XXXX
(can't remember name) and it calls rt parse function again on the
data.
devik

> ¡¡¡¡ I want to send a command "tc qdisc add dev eth0 root tbf rate 220kbit latency 50ms burst 1540" from TC,
> I found that a attribute with type of 1 is added to the nlmsg twice:
> 
>     first time in the function of tc_qdisc_modify() in file of tc_qdisc.c:
> 	"if (k[0])
> 		addattr_l(&req.n, sizeof(req), TCA_KIND, k, strlen(k)+1);"
> 
> 	second time in the function of tbf_parse_opt() in file of q_tbf.c:
>     "addattr_l(n, 2024, TCA_TBF_PARMS, &opt, sizeof(opt));"
> 
> 	the value of TCA_KIND and TCA_TBF_PARAMS is both 1,so the nlmsg consists two attribute with type of 1.
> 
>     when this nlmsg is dealed with in the kernel,I found a problem:
> 
>     in the net/core/rtnetlink.c, function rtnetlink_rev_msg(),when:
> 
> 	"if (nlh->nlmsg_len > min_len) {
> 		int attrlen = nlh->nlmsg_len - NLMSG_ALIGN(min_len);
> 		struct rtattr *attr = (void*)nlh + NLMSG_ALIGN(min_len);
> 
> 		while (RTA_OK(attr, attrlen)) {
> 			unsigned flavor = attr->rta_type;
> 			if (flavor) {
> 				if (flavor > rta_max[sz_idx])
> 					goto err_inval;
> 				rta[flavor-1] = attr;
> 			}
> 			attr = RTA_NEXT(attr, attrlen);
> 		}
> 	}"
> 
> 	at the begining of these lines, the first attribute(TCA_KIND) can be stored in rta[1], but when handling
> the second attribute, it is stored in the same rta[1]! so the first attribute disappeared!!
>     of course the treatment followed will make a mistake.
>     who can tell me why?
> 
> 
> ¡¡¡¡¡¡best regards!
> 
>  				
> ¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Mebius Huang
> ¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡hxgang@csnet4.cs.tsinghua.edu.cn
> ¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡2000-02-21
> ,\x04S
> f¢–)à–+-ü°\x11L)šŠYšÛ=jya¶Ú~ÿùšŠYšÛ=jy\x7f™¨¥™©ÿ–+-ŠwèþV«µÁÎY3¾†Ûiûÿåj»\¢¸?

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