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lguest: documentation III: Drivers

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Documentation: The Drivers

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rusty Russell
2007-07-26 10:41:03 -07:00
committed by Linus Torvalds
parent b2b47c214f
commit e2c9784325
6 changed files with 562 additions and 39 deletions
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218
drivers/net/lguest_net.c
View File

@@ -1,6 +1,13 @@
/* A simple network driver for lguest.
/*D:500
* The Guest network driver.
*
* Copyright 2006 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
* This is very simple a virtual network driver, and our last Guest driver.
* The only trick is that it can talk directly to multiple other recipients
* (ie. other Guests on the same network). It can also be used with only the
* Host on the network.
:*/
/* Copyright 2006 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
@@ -28,23 +35,28 @@
#define MAX_LANS 4
#define NUM_SKBS 8
/*D:530 The "struct lguestnet_info" contains all the information we need to
* know about the network device. */
struct lguestnet_info
{
/* The shared page(s). */
/* The mapped device page(s) (an array of "struct lguest_net"). */
struct lguest_net *peer;
/* The physical address of the device page(s) */
unsigned long peer_phys;
/* The size of the device page(s). */
unsigned long mapsize;
/* The lguest_device I come from */
struct lguest_device *lgdev;
/* My peerid. */
/* My peerid (ie. my slot in the array). */
unsigned int me;
/* Receive queue. */
/* Receive queue: the network packets waiting to be filled. */
struct sk_buff *skb[NUM_SKBS];
struct lguest_dma dma[NUM_SKBS];
};
/*:*/
/* How many bytes left in this page. */
static unsigned int rest_of_page(void *data)
@@ -52,39 +64,82 @@ static unsigned int rest_of_page(void *data)
return PAGE_SIZE - ((unsigned long)data % PAGE_SIZE);
}
/* Simple convention: offset 4 * peernum. */
/*D:570 Each peer (ie. Guest or Host) on the network binds their receive
* buffers to a different key: we simply use the physical address of the
* device's memory page plus the peer number. The Host insists that all keys
* be a multiple of 4, so we multiply the peer number by 4. */
static unsigned long peer_key(struct lguestnet_info *info, unsigned peernum)
{
return info->peer_phys + 4 * peernum;
}
/* This is the routine which sets up a "struct lguest_dma" to point to a
* network packet, similar to req_to_dma() in lguest_blk.c. The structure of a
* "struct sk_buff" has grown complex over the years: it consists of a "head"
* linear section pointed to by "skb->data", and possibly an array of
* "fragments" in the case of a non-linear packet.
*
* Our receive buffers don't use fragments at all but outgoing skbs might, so
* we handle it. */
static void skb_to_dma(const struct sk_buff *skb, unsigned int headlen,
struct lguest_dma *dma)
{
unsigned int i, seg;
/* First, we put the linear region into the "struct lguest_dma". Each
* entry can't go over a page boundary, so even though all our packets
* are 1514 bytes or less, we might need to use two entries here: */
for (i = seg = 0; i < headlen; seg++, i += rest_of_page(skb->data+i)) {
dma->addr[seg] = virt_to_phys(skb->data + i);
dma->len[seg] = min((unsigned)(headlen - i),
rest_of_page(skb->data + i));
}
/* Now we handle the fragments: at least they're guaranteed not to go
* over a page. skb_shinfo(skb) returns a pointer to the structure
* which tells us about the number of fragments and the fragment
* array. */
for (i = 0; i < skb_shinfo(skb)->nr_frags; i++, seg++) {
const skb_frag_t *f = &skb_shinfo(skb)->frags[i];
/* Should not happen with MTU less than 64k - 2 * PAGE_SIZE. */
if (seg == LGUEST_MAX_DMA_SECTIONS) {
/* We will end up sending a truncated packet should
* this ever happen. Plus, a cool log message! */
printk("Woah dude! Megapacket!\n");
break;
}
dma->addr[seg] = page_to_phys(f->page) + f->page_offset;
dma->len[seg] = f->size;
}
/* If after all that we didn't use the entire "struct lguest_dma"
* array, we terminate it with a 0 length. */
if (seg < LGUEST_MAX_DMA_SECTIONS)
dma->len[seg] = 0;
}
/* We overload multicast bit to show promiscuous mode. */
/*
* Packet transmission.
*
* Our packet transmission is a little unusual. A real network card would just
* send out the packet and leave the receivers to decide if they're interested.
* Instead, we look through the network device memory page and see if any of
* the ethernet addresses match the packet destination, and if so we send it to
* that Guest.
*
* This is made a little more complicated in two cases. The first case is
* broadcast packets: for that we send the packet to all Guests on the network,
* one at a time. The second case is "promiscuous" mode, where a Guest wants
* to see all the packets on the network. We need a way for the Guest to tell
* us it wants to see all packets, so it sets the "multicast" bit on its
* published MAC address, which is never valid in a real ethernet address.
*/
#define PROMISC_BIT 0x01
/* This is the callback which is summoned whenever the network device's
* multicast or promiscuous state changes. If the card is in promiscuous mode,
* we advertise that in our ethernet address in the device's memory. We do the
* same if Linux wants any or all multicast traffic. */
static void lguestnet_set_multicast(struct net_device *dev)
{
struct lguestnet_info *info = netdev_priv(dev);
@@ -95,11 +150,14 @@ static void lguestnet_set_multicast(struct net_device *dev)
info->peer[info->me].mac[0] &= ~PROMISC_BIT;
}
/* A simple test function to see if a peer wants to see all packets.*/
static int promisc(struct lguestnet_info *info, unsigned int peer)
{
return info->peer[peer].mac[0] & PROMISC_BIT;
}
/* Another simple function to see if a peer's advertised ethernet address
* matches a packet's destination ethernet address. */
static int mac_eq(const unsigned char mac[ETH_ALEN],
struct lguestnet_info *info, unsigned int peer)
{
@@ -109,6 +167,8 @@ static int mac_eq(const unsigned char mac[ETH_ALEN],
return memcmp(mac+1, info->peer[peer].mac+1, ETH_ALEN-1) == 0;
}
/* This is the function which actually sends a packet once we've decided a
* peer wants it: */
static void transfer_packet(struct net_device *dev,
struct sk_buff *skb,
unsigned int peernum)
@@ -116,76 +176,134 @@ static void transfer_packet(struct net_device *dev,
struct lguestnet_info *info = netdev_priv(dev);
struct lguest_dma dma;
/* We use our handy "struct lguest_dma" packing function to prepare
* the skb for sending. */
skb_to_dma(skb, skb_headlen(skb), &dma);
pr_debug("xfer length %04x (%u)\n", htons(skb->len), skb->len);
/* This is the actual send call which copies the packet. */
lguest_send_dma(peer_key(info, peernum), &dma);
/* Check that the entire packet was transmitted. If not, it could mean
* that the other Guest registered a short receive buffer, but this
* driver should never do that. More likely, the peer is dead. */
if (dma.used_len != skb->len) {
dev->stats.tx_carrier_errors++;
pr_debug("Bad xfer to peer %i: %i of %i (dma %p/%i)\n",
peernum, dma.used_len, skb->len,
(void *)dma.addr[0], dma.len[0]);
} else {
/* On success we update the stats. */
dev->stats.tx_bytes += skb->len;
dev->stats.tx_packets++;
}
}
/* Another helper function to tell is if a slot in the device memory is unused.
* Since we always set the Local Assignment bit in the ethernet address, the
* first byte can never be 0. */
static int unused_peer(const struct lguest_net peer[], unsigned int num)
{
return peer[num].mac[0] == 0;
}
/* Finally, here is the routine which handles an outgoing packet. It's called
* "start_xmit" for traditional reasons. */
static int lguestnet_start_xmit(struct sk_buff *skb, struct net_device *dev)
{
unsigned int i;
int broadcast;
struct lguestnet_info *info = netdev_priv(dev);
/* Extract the destination ethernet address from the packet. */
const unsigned char *dest = ((struct ethhdr *)skb->data)->h_dest;
pr_debug("%s: xmit %02x:%02x:%02x:%02x:%02x:%02x\n",
dev->name, dest[0],dest[1],dest[2],dest[3],dest[4],dest[5]);
/* If it's a multicast packet, we broadcast to everyone. That's not
* very efficient, but there are very few applications which actually
* use multicast, which is a shame really.
*
* As etherdevice.h points out: "By definition the broadcast address is
* also a multicast address." So we don't have to test for broadcast
* packets separately. */
broadcast = is_multicast_ether_addr(dest);
/* Look through all the published ethernet addresses to see if we
* should send this packet. */
for (i = 0; i < info->mapsize/sizeof(struct lguest_net); i++) {
/* We don't send to ourselves (we actually can't SEND_DMA to
* ourselves anyway), and don't send to unused slots.*/
if (i == info->me || unused_peer(info->peer, i))
continue;
/* If it's broadcast we send it. If they want every packet we
* send it. If the destination matches their address we send
* it. Otherwise we go to the next peer. */
if (!broadcast && !promisc(info, i) && !mac_eq(dest, info, i))
continue;
pr_debug("lguestnet %s: sending from %i to %i\n",
dev->name, info->me, i);
/* Our routine which actually does the transfer. */
transfer_packet(dev, skb, i);
}
/* An xmit routine is expected to dispose of the packet, so we do. */
dev_kfree_skb(skb);
/* As per kernel convention, 0 means success. This is why I love
* networking: even if we never sent to anyone, that's still
* success! */
return 0;
}
/* Find a new skb to put in this slot in shared mem. */
/*D:560
* Packet receiving.
*
* First, here's a helper routine which fills one of our array of receive
* buffers: */
static int fill_slot(struct net_device *dev, unsigned int slot)
{
struct lguestnet_info *info = netdev_priv(dev);
/* Try to create and register a new one. */
/* We can receive ETH_DATA_LEN (1500) byte packets, plus a standard
* ethernet header of ETH_HLEN (14) bytes. */
info->skb[slot] = netdev_alloc_skb(dev, ETH_HLEN + ETH_DATA_LEN);
if (!info->skb[slot]) {
printk("%s: could not fill slot %i\n", dev->name, slot);
return -ENOMEM;
}
/* skb_to_dma() is a helper which sets up the "struct lguest_dma" to
* point to the data in the skb: we also use it for sending out a
* packet. */
skb_to_dma(info->skb[slot], ETH_HLEN + ETH_DATA_LEN, &info->dma[slot]);
/* This is a Write Memory Barrier: it ensures that the entry in the
* receive buffer array is written *before* we set the "used_len" entry
* to 0. If the Host were looking at the receive buffer array from a
* different CPU, it could potentially see "used_len = 0" and not see
* the updated receive buffer information. This would be a horribly
* nasty bug, so make sure the compiler and CPU know this has to happen
* first. */
wmb();
/* Now we tell hypervisor it can use the slot. */
/* Writing 0 to "used_len" tells the Host it can use this receive
* buffer now. */
info->dma[slot].used_len = 0;
return 0;
}
/* This is the actual receive routine. When we receive an interrupt from the
* Host to tell us a packet has been delivered, we arrive here: */
static irqreturn_t lguestnet_rcv(int irq, void *dev_id)
{
struct net_device *dev = dev_id;
struct lguestnet_info *info = netdev_priv(dev);
unsigned int i, done = 0;
/* Look through our entire receive array for an entry which has data
* in it. */
for (i = 0; i < ARRAY_SIZE(info->dma); i++) {
unsigned int length;
struct sk_buff *skb;
@@ -194,10 +312,16 @@ static irqreturn_t lguestnet_rcv(int irq, void *dev_id)
if (length == 0)
continue;
/* We've found one! Remember the skb (we grabbed the length
* above), and immediately refill the slot we've taken it
* from. */
done++;
skb = info->skb[i];
fill_slot(dev, i);
/* This shouldn't happen: micropackets could be sent by a
* badly-behaved Guest on the network, but the Host will never
* stuff more data in the buffer than the buffer length. */
if (length < ETH_HLEN || length > ETH_HLEN + ETH_DATA_LEN) {
pr_debug(KERN_WARNING "%s: unbelievable skb len: %i\n",
dev->name, length);
@@ -205,36 +329,72 @@ static irqreturn_t lguestnet_rcv(int irq, void *dev_id)
continue;
}
/* skb_put(), what a great function! I've ranted about this
* function before (http://lkml.org/lkml/1999/9/26/24). You
* call it after you've added data to the end of an skb (in
* this case, it was the Host which wrote the data). */
skb_put(skb, length);
/* The ethernet header contains a protocol field: we use the
* standard helper to extract it, and place the result in
* skb->protocol. The helper also sets up skb->pkt_type and
* eats up the ethernet header from the front of the packet. */
skb->protocol = eth_type_trans(skb, dev);
/* This is a reliable transport. */
/* If this device doesn't need checksums for sending, we also
* don't need to check the packets when they come in. */
if (dev->features & NETIF_F_NO_CSUM)
skb->ip_summed = CHECKSUM_UNNECESSARY;
/* As a last resort for debugging the driver or the lguest I/O
* subsystem, you can uncomment the "#define DEBUG" at the top
* of this file, which turns all the pr_debug() into printk()
* and floods the logs. */
pr_debug("Receiving skb proto 0x%04x len %i type %i\n",
ntohs(skb->protocol), skb->len, skb->pkt_type);
/* Update the packet and byte counts (visible from ifconfig,
* and good for debugging). */
dev->stats.rx_bytes += skb->len;
dev->stats.rx_packets++;
/* Hand our fresh network packet into the stack's "network
* interface receive" routine. That will free the packet
* itself when it's finished. */
netif_rx(skb);
}
/* If we found any packets, we assume the interrupt was for us. */
return done ? IRQ_HANDLED : IRQ_NONE;
}
/*D:550 This is where we start: when the device is brought up by dhcpd or
* ifconfig. At this point we advertise our MAC address to the rest of the
* network, and register receive buffers ready for incoming packets. */
static int lguestnet_open(struct net_device *dev)
{
int i;
struct lguestnet_info *info = netdev_priv(dev);
/* Set up our MAC address */
/* Copy our MAC address into the device page, so others on the network
* can find us. */
memcpy(info->peer[info->me].mac, dev->dev_addr, ETH_ALEN);
/* Turn on promisc mode if needed */
/* We might already be in promisc mode (dev->flags & IFF_PROMISC). Our
* set_multicast callback handles this already, so we call it now. */
lguestnet_set_multicast(dev);
/* Allocate packets and put them into our "struct lguest_dma" array.
* If we fail to allocate all the packets we could still limp along,
* but it's a sign of real stress so we should probably give up now. */
for (i = 0; i < ARRAY_SIZE(info->dma); i++) {
if (fill_slot(dev, i) != 0)
goto cleanup;
}
/* Finally we tell the Host where our array of "struct lguest_dma"
* receive buffers is, binding it to the key corresponding to the
* device's physical memory plus our peerid. */
if (lguest_bind_dma(peer_key(info,info->me), info->dma,
NUM_SKBS, lgdev_irq(info->lgdev)) != 0)
goto cleanup;
@@ -245,22 +405,29 @@ cleanup:
dev_kfree_skb(info->skb[i]);
return -ENOMEM;
}
/*:*/
/* The close routine is called when the device is no longer in use: we clean up
* elegantly. */
static int lguestnet_close(struct net_device *dev)
{
unsigned int i;
struct lguestnet_info *info = netdev_priv(dev);
/* Clear all trace: others might deliver packets, we'll ignore it. */
/* Clear all trace of our existence out of the device memory by setting
* the slot which held our MAC address to 0 (unused). */
memset(&info->peer[info->me], 0, sizeof(info->peer[info->me]));
/* Deregister sg lists. */
/* Unregister our array of receive buffers */
lguest_unbind_dma(peer_key(info, info->me), info->dma);
for (i = 0; i < ARRAY_SIZE(info->dma); i++)
dev_kfree_skb(info->skb[i]);
return 0;
}
/*D:510 The network device probe function is basically a standard ethernet
* device setup. It reads the "struct lguest_device_desc" and sets the "struct
* net_device". Oh, the line-by-line excitement! Let's skip over it. :*/
static int lguestnet_probe(struct lguest_device *lgdev)
{
int err, irqf = IRQF_SHARED;
@@ -290,10 +457,16 @@ static int lguestnet_probe(struct lguest_device *lgdev)
dev->stop = lguestnet_close;
dev->hard_start_xmit = lguestnet_start_xmit;
/* Turning on/off promisc will call dev->set_multicast_list.
* We don't actually support multicast yet */
/* We don't actually support multicast yet, but turning on/off
* promisc also calls dev->set_multicast_list. */
dev->set_multicast_list = lguestnet_set_multicast;
SET_NETDEV_DEV(dev, &lgdev->dev);
/* The network code complains if you have "scatter-gather" capability
* if you don't also handle checksums (it seem that would be
* "illogical"). So we use a lie of omission and don't tell it that we
* can handle scattered packets unless we also don't want checksums,
* even though to us they're completely independent. */
if (desc->features & LGUEST_NET_F_NOCSUM)
dev->features = NETIF_F_SG|NETIF_F_NO_CSUM;
@@ -325,6 +498,9 @@ static int lguestnet_probe(struct lguest_device *lgdev)
}
pr_debug("lguestnet: registered device %s\n", dev->name);
/* Finally, we put the "struct net_device" in the generic "struct
* lguest_device"s private pointer. Again, it's not necessary, but
* makes sure the cool kernel kids don't tease us. */
lgdev->private = dev;
return 0;
@@ -352,3 +528,11 @@ module_init(lguestnet_init);
MODULE_DESCRIPTION("Lguest network driver");
MODULE_LICENSE("GPL");
/*D:580
* This is the last of the Drivers, and with this we have covered the many and
* wonderous and fine (and boring) details of the Guest.
*
* "make Launcher" beckons, where we answer questions like "Where do Guests
* come from?", and "What do you do when someone asks for optimization?"
*/