netgraph/ng_tag: Variable length data can not be set for all length

[donner]

Summary

ng_tag can operate on arbitrary data of mbuf_tags.
This should work for any data sets.

ngctl
+ mkpeer . tag t t
+ msg t sethookin { thisHook="t" tag_len=4 tag_data=[1] }

works. But the following does not:

+ msg t sethookin { thisHook="t" tag_len=1 tag_data=[1] }
ngctl: send msg: Invalid argument

Especially in the case of checking for mbuf_tag values, the length
of checked data is important.

The reason behind this behavior is, that the record size
is padded to the next multiple of the alignment. Therefore
it's sufficient to check for large enough data received.

PR: 241462

Test Plan

+ mkpeer . tag t t
+ msg t sethookin { thisHook="t" tag_len=4 tag_data=[1] }
+ msg t sethookin { thisHook="t" tag_len=1 tag_data=[1] }
+ msg t gethookin "t"
Rec'd response "gethookin" (2) from "[72]:":
Args:   { thisHook="t" tag_len=1 tag_data=[ 0x1 ] }

[donner]

sys/netgraph/ng_tag.c

366–367

Reformatted to more readability and conformance to style(9)

[afedorov]

I think you need to add people with good knowledge of the netgraph to the reviewers: JulianElischer, Gleb Smirnoff and Alexander Motin. Because apparently not all are subscribed to the network mailing list.

[donner]

Ping?

[donner]

Rebase to current

[donner]

Revert errornous comparsion

[donner]

Rebase to r366170.

[kp]

Approved by: kp (mentor)