new file mode 100644
@@ -0,0 +1,156 @@
+.TH STAB 8 "25 February 2009" iproute2 Linux
+.
+.SH NAME
+tc\-stab \- Generic size table manipulations
+.
+.SH SYNOPSIS
+.nf
+tc qdisc add ... stab \\
+.RS 4
+[ \fBmtu\fR BYTES ] [ \fBtsize\fR SLOTS ] \\
+[ \fBmpu\fR BYTES ] [ \fBoverhead\fR BYTES ] [ \fBlinklayer\fR TYPE ] ...
+.RE
+
+TYPE := adsl | atm | ethernet
+.fi
+
+For the description of BYTES \- please refer to the \fBUNITS\fR
+section of \fBtc\fR(8).
+
+.IP \fBmtu\fR 4
+.br
+maximum packet size we create size table for, assumed 2048 if not specified explicitly
+.IP \fBtsize\fR
+.br
+required table size, assumed 512 if not specified explicitly
+.IP \fBmpu\fR
+.br
+minimum packet size used in computations
+.IP \fBoverhead\fR
+.br
+per\-packet size overhead (can be negative) used in computations
+.IP \fBlinklayer\fR
+.br
+required linklayer adaptation.
+.PP
+.
+.SH DESCRIPTION
+.
+Size tables allow manipulation of packet size, as seen by whole scheduler
+framework (of course, the actual packet size remains the same). Adjusted packet
+size is calculated only once \- when a qdisc enqueues the packet. Initial root
+enqueue initializes it to the real packet's size.
+
+Each qdisc can use different size table, but the adjusted size is stored in
+area shared by whole qdisc hierarchy attached to the interface (technically,
+it's stored in skb). The effect is, that if you have such setup, the last qdisc
+with a stab in a chain "wins". For example, consider HFSC with simple pfifo
+attached to one of its leaf classes. If that pfifo qdisc has stab defined, it
+will override lengths calculated during HFSC's enqueue, and in turn, whenever
+HFSC tries to dequeue a packet, it will use potentially invalid size in its
+calculations. Normal setups will usually include stab defined only on root
+qdisc, but further overriding gives extra flexibility for less usual setups.
+
+Initial size table is calculated by \fBtc\fR tool using \fBmtu\fR and
+\fBtsize\fR parameters. The algorithm sets each slot's size to the smallest
+power of 2 value, so the whole \fBmtu\fR is covered by the size table. Neither
+\fBtsize\fR, nor \fBmtu\fR have to be power of 2 value, so the size
+table will usually support more than is required by \fBmtu\fR.
+
+For example, with \fBmtu\fR\~=\~1500 and \fBtsize\fR\~=\~128, a table with 128
+slots will be created, where slot 0 will correspond to sizes 0\-16, slot 1 to
+17\~\-\~32, \&..., slot 127 to 2033\~\-\~2048. Note, that the sizes
+are shifted 1 byte (normally you would expect 0\~\-\~15, 16\~\-\~31, \&...,
+2032\~\-\~2047). Sizes assigned to each slot depend on \fBlinklayer\fR parameter.
+
+Stab calculation is also safe for an unusual case, when a size assigned to a
+slot would be larger than 2^16\-1 (you will lose the accuracy though).
+
+During kernel part of packet size adjustment, \fBoverhead\fR will be added to
+original size, and after subtracting 1 (to land in the proper slot \- see above
+about shifting by 1 byte) slot will be calculated. If the size would cause
+overflow, more than 1 slot will be used to get the final size. It of course will
+affect accuracy, but it's only a guard against unusual situations.
+
+Currently there're two methods of creating values stored in the size table \-
+ethernet and atm (adsl):
+
+.IP ethernet 4
+.br
+This is basically 1\-1 mapping, so following our example from above
+(disregarding \fBmpu\fR for a moment) slot 0 would have 8, slot 1 would have 16
+and so on, up to slot 127 with 2048. Note, that \fBmpu\fR\~>\~0 must be
+specified, and slots that would get less than specified by \fBmpu\fR, will get
+\fBmpu\fR instead. If you don't specify \fBmpu\fR, the size table will not be
+created at all, although any \fBoverhead\fR value will be respected during
+calculations.
+.IP "atm, adsl"
+.br
+ATM linklayer consists of 53 byte cells, where each of them provides 48 bytes
+for payload. Also all the cells must be fully utilized, thus the last one is
+padded if/as necessary.
+
+When size table is calculated, adjusted size that fits properly into lowest
+amount of cells is assigned to a slot. For example, a 100 byte long packet
+requires three 48\-byte payloads, so the final size would require 3 ATM cells
+\- 159 bytes.
+
+For ATM size tables, 16\~bytes sized slots are perfectly enough. The default
+values of \fBmtu\fR and \fBtsize\fR create 4\~bytes sized slots.
+.PP
+.
+.SH "TYPICAL OVERHEADS"
+The following values are typical for different adsl scenarios (based on
+\fB[1]\fR and \fB[2]\fR):
+
+.nf
+LLC based:
+.RS 4
+PPPoA \- 14 (PPP \- 2, ATM \- 12)
+PPPoE \- 40+ (PPPoE \- 8, ATM \- 18, ethernet 14, possibly FCS \- 4+padding)
+Bridged \- 32 (ATM \- 18, ethernet 14, possibly FCS \- 4+padding)
+IPoA \- 16 (ATM \- 16)
+.RE
+
+VC Mux based:
+.RS 4
+PPPoA \- 10 (PPP \- 2, ATM \- 8)
+PPPoE \- 32+ (PPPoE \- 8, ATM \- 10, ethernet 14, possibly FCS \- 4+padding)
+Bridged \- 24+ (ATM \- 10, ethernet 14, possibly FCS \- 4+padding)
+IPoA \- 8 (ATM \- 8)
+.RE
+.fi
+\p There're few important things regarding the above overheads:
+.
+.IP \(bu 4
+IPoA in LLC case requires SNAP, instead of LLC\-NLPID (see rfc2684) \- this is
+the reason, why it actually takes more space than PPPoA.
+.IP \(bu
+In rare cases, FCS might be preserved on protocols that include ethernet frame
+(Bridged and PPPoE). In such situation, any ethernet specific padding
+guaranteeing 64 bytes long frame size has to be included as well (see rfc2684).
+In the other words, it also guarantees that any packet you send will take
+minimum 2 atm cells. You should set \fBmpu\fR accordingly for that.
+.IP \(bu
+When size table is consulted, and you're shaping traffic for the sake of
+another modem/router, ethernet header (without padding) will already be added
+to initial packet's length. You should compensate for that by subtracting 14
+from the above overheads in such case. If you're shaping directly on the router
+(for example, with speedtouch usb modem) using ppp daemon, layer2 header will
+not be added yet.
+
+For more thorough explanations, please see \fB[1]\fR and \fB[2]\fR.
+.
+.SH "SEE ALSO"
+.
+\fBtc\fR(8), \fBtc\-hfsc\fR(7), \fBtc\-hfsc\fR(8),
+.br
+\fB[1]\fR http://ace\-host.stuart.id.au/russell/files/tc/tc\-atm/
+.br
+\fB[2]\fR http://www.faqs.org/rfcs/rfc2684.html
+
+Please direct bugreports and patches to: <netdev@vger.kernel.org>
+.
+.SH "AUTHOR"
+.
+Manpage created by Michal Soltys (soltys@ziu.info)
@@ -155,12 +155,12 @@ int tc_calc_size_table(struct tc_sizespec *s, __u16 **stab)
}
if (s->mtu == 0)
- s->mtu = 2047;
+ s->mtu = 2048;
if (s->tsize == 0)
s->tsize = 512;
s->cell_log = 0;
- while ((s->mtu >> s->cell_log) > s->tsize - 1)
+ while ((s->mtu - 1 >> s->cell_log) > s->tsize - 1)
s->cell_log++;
*stab = malloc(s->tsize * sizeof(__u16));
@@ -32,11 +32,12 @@ static void stab_help(void)
fprintf(stderr,
"Usage: ... stab [ mtu BYTES ] [ tsize SLOTS ] [ mpu BYTES ] \n"
" [ overhead BYTES ] [ linklayer TYPE ] ...\n"
- " mtu : max packet size we create rate map for {2047}\n"
+ "TYPE := adsl | atm | ethernet\n"
+ " mtu : max packet size we create size table for {2048}\n"
" tsize : how many slots should size table have {512}\n"
- " mpu : minimum packet size used in rate computations\n"
- " overhead : per-packet size overhead used in rate computations\n"
- " linklayer : adapting to a linklayer e.g. atm\n"
+ " mpu : minimum packet size used in size table computations\n"
+ " overhead : per-packet size overhead used in size table computations\n"
+ " linklayer : required linklayer adaptation, (adsl and atm are synonyms)\n"
"Example: ... stab overhead 20 linklayer atm\n");
return;