| authors | state |
|---|---|
George V. Neville-Neil <[email protected]> |
draft |
Data in BSD derived network stacks resides in mbuf chains. The D
language does not currently have any routines for giving D programs
access to chained mbuf data. The current RFD aims to add a new D
subroutine for use by D programs in looking at data in an mbuf
chain.
One new sub-routines will be defined to give access to data in mbuf
chains. The interface is described in the following sections.
copyoutmbuf(struct mbuf *m, size_t length, [size_t offset])
The copyoutmbuf subroutine operates in a similar manner to the
currently existing copy interfaces in OpenDTrace It has two required
arguments: a pointer to an mbuf structure (struct mbuf *) and a
length. If the length is specified as 0 then the subroutine will
attempt to copy out all of the data in the mbuf chain, starting from
the beginning. It is possible for D's limited scratch space to run
out during this operation and so the subroutine may fail with an out
of memory condition. An optional third argument, offset, allows the
caller to request data starting after the beginning of the mbuf
chain, which can be used to skip over headers that are not of interest
to the caller.
The following is an example of using the copyoutmbuf routine in a D
one liner. Show the first 64 bytes of the data that arrives in an
mbuf passed to tcp_input().
dtrace -n ':::tcp_input:entry { tracemem(copyoutmbuf(*args[0], 64), 64); }'
dtrace: description ':::tcp_input:entry ' matched 1 probe
CPU ID FUNCTION:NAME
3 34345 tcp_input:entry
0 1 2 3 4 5 6 7 8 9 a b c d e f 0123456789abcdef
0: 45 10 00 34 46 f4 40 00 40 06 70 0a c0 a8 01 01 E..4F.@[email protected].....
10: c0 a8 01 64 3d 3c 00 16 70 7d fa 57 c2 cc f1 4b ...d=<..p}.W...K
20: 80 10 04 10 b5 a5 00 00 01 01 08 0a 3a c8 04 ae ............:...
30: 94 3c 09 5f 00 00 00 00 00 00 00 00 00 00 00 00 .<._............
This second example skips the first 20 bytes of data, which should be the IPv4 header:
dtrace -n ':::tcp_input:entry { tracemem(copyoutmbuf(*args[0], 64, 20), 64); }'
dtrace: description ':::tcp_input:entry ' matched 1 probe
CPU ID FUNCTION:NAME
3 34345 tcp_input:entry
0 1 2 3 4 5 6 7 8 9 a b c d e f 0123456789abcdef
0: 3d 3c 00 16 70 7d fd 03 c2 cd 25 33 80 10 04 10 =<..p}....%3....
10: 1c a6 00 00 01 01 08 0a 3a c8 b5 e5 94 3c ba 92 ........:....<..
20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
Both of the new public subroutines described above depend on a single,
new, internal interface, dtrace_mbuf_copydata(), which operates in a
similar manner to the FreeBSD kernel's mbuf_copydata() routine but
which is implemented using the OpenDTrace safe copy routines.
The new subroutine has no effect on existing systems as the they are completely new, and do not modify existing interfaces.
The version of DTrace will be increased once the new subroutine is added.
The new subroutine present no new security issues for the OpenDTrace system.