Support configurable MTU in Intel82599 driver

The MTU is now configurable individually for each instance of the
driver.  The MTU includes the L2 header, but not the CRC.  The driver
enables jumbo frames if the MTU exceeds 1514 bytes.  Receive buffers
must be large enough to hold a full-sized packet.  Packets which
exceed the MTU are discarded by transmit().

src/apps/intel/intel10g.lua

@@ -25,10 +25,34 @@ num_descriptors = 512
 --num_descriptors = 32
 
 -- Defaults for configurable items
-local default = { snmp = {
-		     status_timer = 5, -- Interval for IF status check and MIB update
-		  }
-	       }
+local default = {
+   -- The MTU configured through the MAXFRS.MFS register includes the
+   -- Ethernet header and CRC. It is limited to 65535 bytes.  We use
+   -- the convention that the configurable MTU includes the Ethernet
+   -- header but not the CRC.  This is "natural" in the sense that the
+   -- unit of data handed to the driver contains a complete Ethernet
+   -- packet.
+   --
+   -- For untagged packets, the Ethernet overhead is 14 bytes.  If
+   -- 802.1q tagging is used, the Ethernet overhead is increased by 4
+   -- bytes per tag.  This overhead must be included in the MTU if
+   -- tags are handled by the software.  However, the NIC always
+   -- accepts packets of size MAXFRS.MFS+4 and MAXFRS.MFS+8 if single-
+   -- or double tagged packets are received (see section 8.2.3.22.13).
+   -- In this case, we will actually accept packets which exceed the
+   -- MTU.
+   --
+   -- XXX If hardware support for VLAN tag adding or stripping is
+   -- enabled, one should probably not include the tags in the MTU.
+   --
+   -- The default MTU allows for an IP packet of a total size of 9000
+   -- bytes without VLAN tagging.
+   mtu = 9014,
+
+   snmp = {
+      status_timer = 5, -- Interval for IF status check and MIB update
+   }
+}
 
 local function pass (...) return ... end
 
@@ -38,6 +62,7 @@ local M_sf = {}; M_sf.__index = M_sf
 
 function new_sf (conf)
    local dev = { pciaddress = conf.pciaddr, -- PCI device address
+                 mtu = (conf.mtu or default.mtu),
                  fd = false,       -- File descriptor for PCI memory
                  r = {},           -- Configuration registers
                  s = {},           -- Statistics registers
@@ -225,16 +250,23 @@ function M_sf:init_receive ()
    self.r.RXCTRL:clr(bits{RXEN=0})
    self:set_promiscuous_mode() -- NB: don't need to program MAC address filter
    self.r.HLREG0(bits{
-      TXCRCEN=0, RXCRCSTRP=1, JUMBOEN=2, rsv2=3, TXPADEN=10,
+      TXCRCEN=0, RXCRCSTRP=1, rsv2=3, TXPADEN=10,
       rsvd3=11, rsvd4=13, MDCSPD=16
    })
-   self.r.MAXFRS(lshift(9000+18, 16))
+   if self.mtu > 1514 then
+      self.r.HLREG0:set(bits{ JUMBOEN=2 })
+      -- MAXFRS is set to a hard-wired default of 1518 if JUMBOEN is
+      -- not set.  The MTU does *not* include the 4-byte CRC, but
+      -- MAXFRS does.
+      self.r.MAXFRS(lshift(self.mtu+4, 16))
+   end
    self:set_receive_descriptors()
    self.r.RXCTRL:set(bits{RXEN=0})
    return self
 end
 
 function M_sf:set_rx_buffersize(rx_buffersize)
+   assert(rx_buffersize >= self.mtu)
    rx_buffersize = math.min(16, math.floor((rx_buffersize or 16384) / 1024))  -- size in KB, max 16KB
    assert (rx_buffersize > 0, "rx_buffersize must be more than 1024")
    self.rx_buffersize = rx_buffersize * 1024
@@ -285,10 +317,14 @@ end
 local txdesc_flags = bits{ifcs=25, dext=29, dtyp0=20, dtyp1=21, eop=24}
 
 function M_sf:transmit (p)
-   self.txdesc[self.tdt].address = memory.virtual_to_physical(p.data)
-   self.txdesc[self.tdt].options = bor(p.length, txdesc_flags, lshift(p.length+0ULL, 46))
-   self.txpackets[self.tdt] = p
-   self.tdt = band(self.tdt + 1, num_descriptors - 1)
+   if p.length > self.mtu then
+      packet.free(p)
+   else
+      self.txdesc[self.tdt].address = memory.virtual_to_physical(p.data)
+      self.txdesc[self.tdt].options = bor(p.length, txdesc_flags, lshift(p.length+0ULL, 46))
+      self.txpackets[self.tdt] = p
+      self.tdt = band(self.tdt + 1, num_descriptors - 1)
+   end
 end
 
 function M_sf:sync_transmit ()
@@ -467,6 +503,7 @@ local M_pf = {}; M_pf.__index = M_pf
 
 function new_pf (conf)
    local dev = { pciaddress = conf.pciaddr, -- PCI device address
+                 mtu = (conf.mtu or default.mtu),
                  r = {},           -- Configuration registers
                  s = {},           -- Statistics registers
                  qs = {},          -- queue statistic registers