debug.nr

早期freebsd实现

are used.
The program \fItpdiscard\fR or a simple file transfer
is run with various window
and maximum TPDU sizes, various acknoledgment strategies, and
various retransmission strategies,
and the activity is observed with the trace.
The debug option
\fBT.reneg\fR
must be used to fake a reneging of credit, since
the ARGO transport entity does not renege its advertised credit
under normal operation.
At the beginning of a connection a closed window may almost always
be observed.
The receiving user process may be stopped 
to force a window to shut down.
The interesting statistics are
.(b
.nf
\fIn\fR times local cdt reneged (receiving)
\fIn\fR foreign window closed (sending)
\fIn\fR faked reneging of cdt
\fIn\fR DT TPDUs (sent)
\fIn\fR DT TPDUs (received)
\fIn\fR AK TPDUs (sent)
\fIn\fR AK TPDUs (received)
ACK reasons:
\fIn\fR not acked immediately
\fIn\fR strategy==each
\fIn\fR strategy==fullwindow
\fIn\fR duplicate DT
\fIn\fR EOTSDU
\fIn\fR reordered
\fIn\fR user rcvd
\fIn\fR fcc reqd
.fi
.)b
.sh 4 "Retransmission and retention until acknowledgment:"
.pp
To observe that the sender retains TPDUs until they are
acknowledged, one needs only to use the
\fBT.drop\fR
debug option to cause TPDUs to be dropped by the receiving side.
They are then retransmitted by the sender
and finally dropped when the acknowledgment arrives.
That the buffers used to hold retained TPDUs are freed 
can be observed by 
running \fInetstat(8)\fR with the -m option
on a quiescent system to observe the number of mbufs in use,
then
running a test with the 
\fBT.drop\fR debug option on to cause retransmission,
and 
finally
running netstat -m again after the test is over,
to see that all the mbufs have been freed by TP.
The actual retransmission activity can be observed in a trace
with the
\fBT.ndata, \fR
\fBT.emit\fR and 
\fBT.input\fR trace options.
The retransmission strategy to be used is controlled by the
ARGO directory service.
The statistics
.(b
.nf
\fIn\fR DT (retransmissions)
\fIn\fR XPD (retransmissions)
\fIn\fR CR (retransmissions)
\fIn\fR CC (retransmissions)
\fIn\fR DR (retransmissions)
.fi
.)b
.lp
indicate the number of retransmissions that actually occurred.
.sh 4 "Timers:"
.pp
The debug and trace option
\fBT.timer\fR
dumps information about the timers as they are set,
as they are cancelled, and as they expire.
The statistics
.(b
.nf
\fIn\fR ticks 
\fIn\fR timers set 
\fIn\fR timers expired 
\fIn\fR timers cancelled
\fIn\fR inactive timers cancelled
\fIn\fR connections dropped due to retrans limit
\fIn\fR CCs sent to zero dref
.fi
.)b
.lp
are printed for both the E-type timers and for the C-type timers.
The effect of timers can be seen by observing retransmissions.
Two simple ways to force retransmissions are:
.np
to use the \fBT.zdref\fR debug option,
which causes CCs to contain a zero destination reference,
so that connection establishment will time out, and
.np
to attempt to open a connection to a transport selector on which
no process is listening.
Either of these actions, along with the 
\fBT.connect\fR
trace or debug option will permit
observation of the timeout facilities.
.sh 4 "TPDU creation and parsing:"
.pp
TPDUs are created for output in 
\fItp_emit()\fR.
The 
\fBT.emit\fR
trace
option dumps TPDUs as they are transmitted.
\fITp_input()\fR parses TPDUs on input.
The 
\fBT.input\fR
trace
option dumps TPDUs as they are received.
The debug options \fBT.emit\fR and \fBT.input\fR dump a lot of excess information
to the console, and are used primarily for debugging
extremely pathological behavior.
.pp
By tracing the execution of 
\fItpdiscard\fR or a simple file transfer,
with a variety protocol and service options,
using the 
\fBT.connect,\fR
\fBT.emit,\fR
\fBT.input,\fR
\fBT.ndata,\fR
\fBT.aks,\fR
\fBT.akr,\fR
and 
\fBT.xpd\fR
options,
one can verify the correct placement of TPDU options
on all types of TPDUs.
The interesting statistics are
.(b
.nf
\fIn\fR variable parameters ignored 
\fIn\fR invalid parameter codes
\fIn\fR invalid parameter values
\fIn\fR invalid dutypes
\fIn\fR invalid negotiation failures
\fIn\fR invalid destinagion referencess
\fIn\fR invalid suffix parameters
\fIn\fR invalid checksums
\fIn\fR connections used extended format
\fIn\fR connections allowed transport XPD
\fIn\fR connections turned off checksumming
\fIn\fR TP 4 connections 
\fIn\fR TP 0 connections 
.fi
.)b
.sh 4 "Separation and concatenation:"
.pp
Concatenation is not supported by this implementation.
Separation is supported, however, and to test separation,
some sort of concatenated TPDUs had to be created.
The code for this is no longer supported.
After testing locally with some temporary code to create concatenated
TPDUs,
the ARGO transport implementation was tested with another transport
implementation that does generate concatenated TPDUs.
The interesting statistics are:
.(b
.nf
\fIn\fR concatenated TPDUs
\fIn\fR TPDUs input
.fi
.)b
.sh 4 "Length limits for TPDUs:"
.pp
Some TPDUs may take user data:
the CR, CC, DR, DT, and XPD.
All of these but the DT TPDU have limits to the amount
of data they may carry.
The limits are enforced for CR, CC, and DR TPDUs by
\fItp_ctloutput()\fR,
the routine that accepts data from the user.
The limit for XPD TPDUs is enforced by
\fItp_usrreq()\fR, which accepts expedited
data from the user.
To test the effectiveness of the checks on output, one may attempt
to send expedited data with amounts larger than the limit (16 bytes).
.pp
On input the limits are checked in
\fItp_input()\fR.
To test the effectiveness of the checks on input, it was necessary
to create an illegally large TPDU.
The
\fBT.badsize\fR
debug option
does this - it will turn a legitimate
XPD TPDU into a XPD TPDU with 18 bytes
of expedited data.
The interesting statistics are:
.(b
.nf
\fIn\fR illegally large XPD TPDU
\fIn\fR invalid length
.fi
.)b
.sh 4 "Frozen References:"
.pp
The key issue here is to see that references are not reassigned
until the reference timer expires.
This can be observed by watching the timer activity as described
above and by observing the reference numbers chosen for sockets
with the \fBT.emit\fR
or \fBT.input\fR trace options, which trace the TPDU headers.
.sh 4 "Inactivity Control:"
.pp
Inactivity control can be observed by turning on the trace options
\fBT.aks\fR, \fBT.akr\fR and \fBT.emit\fR
during a simple file transfer.
In the middle of the transfer, if the sender process
is stopped, both TP entities continue
to send acknowledgments. 
This can be observed in the trace.
If the file tranfer is between machines, taking down one of the machines
will cause the inactivity timer on the other machine to expire.
The TP entity will respond to this by sending a DR TPDU
to close the connection, which can be observed in the trace.
The expiration of the timer can be observed in a trace if the
\fBT.driver\fR option is used.
This option traces all events and state changes in the 
TP
finite state machine.
.sh 4 "Connection establishment:"
.pp
The process of connection establishment can be observed with the
\fBT.connect\fR
trace and debug options, and
the 
\fBT.driver \fR
trace option.
Various states of the connection establishment state machine
may be observed with the
the debug option
\fBT.zdref\fR.
This option
causes \fItp_input()\fR
to change the foreign reference on an incoming CC TPDU to zero,
eventually causing the CC TPDU to be dropped,
retransmissions of the CC to occur,
and the connection to time out before being established.
The statistics of interest are:
.(b
.nf
\fIn\fR CCs sent to zero dref
\fIn\fR invalid dest refs
\fIn\fR CC (received)
\fIn\fR CC (sent)
\fIn\fR CC (retransmitted)
\fIn\fR (connections) timed out on retrans
.fi
.)b
.sh 4 "Disconnection:"
.pp
Various states of the connection breakdown part of the state machine
may be observed with the
the trace options
\fBT.input\fR
or
\fBT.emit\fR, 
\fBT.driver\fR
and
running the
discard or file transfer programs.
.sh 4 "Association of TPDUs with Transport Connection:"
.pp
The problem of locating a transport connection
given a TPDU is handled in 
\fItp_input()\fR in one of two ways.
For an incoming CR TPDU, the transport suffix
is used to locate a transport protocol
control block (PCB), to which a transport
connection is made by creating a new socket and PCB.
For all other TPDU types, the destination reference is used
to locate the appropriate transport connection.
This is done by scanning the list of reference blocks.
Debug and trace options
were used to debug these sections of code but have since been
removed due to their effect on the readability 
and maintainability of this code.
The trace options
\fBT.connect\fR
and
\fBT.newsock\fR
creates trace records that contain the address of the
socket as well as that of the PCB
when a socket is opened.
When a TPDU arrives for a given socket,
the trace records created by the
\fBT.input \fR
option will also contain the address of the PCB that is found
in 
\fItp_input()\fR.
These two addresses can be compared in the trace output to observe
that the proper association is made.
.sh 4 "Protocol Errors and the ER TPDU:"
.pp
Certain types of errors are intended to evoke the response
from the TP entity of sending an ER or a DR TPDU.
The routine
\fItp_error_emit()\fR
creates ER and DR TPDUs for this purpose.
The debug and trace option
\fBT.erroremit\fR
dumps information about the activity of this routine.
Since ER TPDUs are not generated under normal circumstances,
the parsing of ER TPDUs was tested in this
implementation by code that generated (illegitimate) ER TPDUs,
This code was removed because it significantly complicated code maintenance.
.sh 4 "User Interface:"
.pp
The debug and trace options
\fBT.request\fR, 
\fBT.params,\fR
\fBT.indication\fR 
and
\fBT.syscall\fR and
dump information about the user interface.
Most of the debugging code added to the socket-layer
routines for debugging has since been removed so that
the source (which is functionally unchanged from the 4.3 release)
would not unnecessarily be changed.
\fIRlogin.iso\fR, the TP version of remote login,
exercises some of the original BSD data transfer system calls 
(\fIread()\fR and \fIwrite()\fR)
rather than \fIsendv()\fR and \fIrecv()\fR.
The interesting statistics are
.(b
.nf
\fIn\fR EOT indications
\fIn\fR user rcvd
\fIn\fR connections used extended format
\fIn\fR connections allowed transport XPD
\fIn\fR connections turned off checksumming
\fIn\fR TP 4 connections 
\fIn\fR TP 0 connections 
.fi
.)b