SchOS/kernel/net/net.c

// SPDX-License-Identifier: Apache-2.0
//
// The network thread, and the one place the TCP/IP stack is started.
//
// lwIP with NO_SYS=1 has no threads of its own, so something has to feed it
// received frames and run its timers. That something is a kernel thread rather
// than the e1000 interrupt handler, and the reason is the lock: a call into
// lwIP can reach the driver, the driver can sleep, and an interrupt handler
// cannot. So the interrupt keeps doing what it always did -- clear the cause
// register -- and this thread polls.
//
// Polling costs a wakeup every few milliseconds when the link is idle. The
// alternative, waking this thread from the interrupt, is a worthwhile change
// later; it is deliberately not the first version, because a receive path that
// is woken from an interrupt is much harder to debug than one that is asked.

#include "types.h"
#include "defs.h"
#include "param.h"
#include "spinlock.h"
#include "sleeplock.h"
#include "proc.h"

#include "lwip/opt.h"
#include "lwip/init.h"
#include "lwip/timeouts.h"
#include "lwip/netif.h"
#include "lwip/dhcp.h"
#include "lwip/ip4_addr.h"

// Wait until the next timer tick. `ticks` advances at 100 Hz, so this is a
// sleep of up to 10 ms -- and, more importantly, it is the kernel's only timed
// sleep: there is no higher-resolution timer to wait on. The lwIP lock must not
// be held across it, or nothing else could touch the stack while the link is
// idle, which is most of the time.
static void
wait_tick(void)
{
    acquire(&tickslock);
    uint start = ticks;
    while (ticks == start)
        sleep(&ticks, &tickslock);
    release(&tickslock);
}

static int net_started;

// Set once DHCP has bound, so `ifconfig`-ish output and /proc/net have
// something true to say rather than reporting 0.0.0.0 forever.
static int net_bound;

int
net_is_up(void)
{
    return net_bound;
}

static void
net_thread(void)
{
    // lwIP's own initialisation has to happen in this thread, not in main():
    // it allocates from lwIP's pools and registers timers, and doing that
    // before there is a process context means doing it somewhere that cannot
    // sleep if the allocator ever needs to.
    lwip_sys_init();

    lwip_sys_lock();
    lwip_init();
    if (net_e1000_attach() != 0) {
        lwip_sys_unlock();
        cprintf("net: no e1000; the network thread has nothing to drive\n");
        // Not a panic and not an exit: a kernel thread must never return, and
        // a machine with no NIC is an ordinary machine.
        for (;;)
            wait_tick();
    }
    struct netif *nif = net_e1000_netif();
    dhcp_start(nif);
    lwip_sys_unlock();

    cprintf("net: lwIP %d.%d.%d up, requesting an address\n",
            LWIP_VERSION_MAJOR, LWIP_VERSION_MINOR, LWIP_VERSION_REVISION);

    int announced = 0;

    for (;;) {
        int moved;

        lwip_sys_lock();
        moved = net_e1000_poll();
        sys_check_timeouts();

        // Report the address once, when it first arrives. Anyone who has spent
        // an evening wondering whether the guest has an address at all wants
        // this on the console rather than in a file they have to know about.
        if (!announced && !ip4_addr_isany_val(*netif_ip4_addr(nif))) {
            const ip4_addr_t *a  = netif_ip4_addr(nif);
            const ip4_addr_t *m  = netif_ip4_netmask(nif);
            const ip4_addr_t *gw = netif_ip4_gw(nif);
            cprintf("net: %d.%d.%d.%d/%d.%d.%d.%d via %d.%d.%d.%d\n",
                    ip4_addr1(a),  ip4_addr2(a),  ip4_addr3(a),  ip4_addr4(a),
                    ip4_addr1(m),  ip4_addr2(m),  ip4_addr3(m),  ip4_addr4(m),
                    ip4_addr1(gw), ip4_addr2(gw), ip4_addr3(gw), ip4_addr4(gw));
            announced = 1;
            net_bound = 1;
        }
        lwip_sys_unlock();

        // Busy while there is traffic, idle otherwise. Sleeping even 1 ms with
        // frames waiting would cap throughput at one burst per tick.
        if (moved == 0)
            wait_tick();
    }
}

/* ------------------------------------------------------------------ */
/* /proc/netif                                                         */
/* ------------------------------------------------------------------ */
//
// Named netif rather than net, and that is deliberate: on Linux /proc/net is a
// *directory* of a dozen files, and putting a plain file there would mean
// anything reaching for the familiar /proc/net/dev got ENOTDIR from a path that
// looks like it exists. This is one interface's state, so it is named for what
// it holds and leaves the Linux name free for the day there is a directory to
// put under it.
//
// No snprintf in the kernel, so this appends by hand in the same style as
// kernel/dev/pci.c.

static int
put_str(char *out, const char *s)
{
    int n = 0;
    while (s[n]) { out[n] = s[n]; n++; }
    return n;
}

static int
put_u(char *out, uint64 v)
{
    char tmp[24];
    int  i = 0, n = 0;

    if (v == 0) { out[0] = '0'; return 1; }
    while (v && i < (int)sizeof(tmp)) { tmp[i++] = '0' + (char)(v % 10); v /= 10; }
    while (i--) out[n++] = tmp[i];
    return n;
}

static int
put_ip4(char *out, const ip4_addr_t *a)
{
    int n = 0;
    n += put_u(out + n, ip4_addr1(a)); out[n++] = '.';
    n += put_u(out + n, ip4_addr2(a)); out[n++] = '.';
    n += put_u(out + n, ip4_addr3(a)); out[n++] = '.';
    n += put_u(out + n, ip4_addr4(a));
    return n;
}

static int
put_mac(char *out, const unsigned char *m)
{
    static const char d[] = "0123456789abcdef";
    int n = 0;
    for (int i = 0; i < 6; i++) {
        if (i) out[n++] = ':';
        out[n++] = d[m[i] >> 4];
        out[n++] = d[m[i] & 0xF];
    }
    return n;
}

// One "name value" pair per line, which is the shape /proc/schfs and
// /proc/fsstat already use here -- a reader that can scan one can scan all of
// them.
static int
put_field(char *out, const char *name)
{
    int n = put_str(out, name);
    while (n < 12)
        out[n++] = ' ';
    return n;
}

int
net_info(char *buf, int cap)
{
    int len = 0;

    if (cap < 512)
        return 0;

    if (!net_started) {
        len += put_field(buf + len, "state");
        len += put_str(buf + len, e1000_present() ? "down\n" : "no interface\n");
        return len;
    }

    struct netif *nif = net_e1000_netif();

    lwip_sys_lock();

    len += put_field(buf + len, "interface");
    buf[len++] = nif->name[0];
    buf[len++] = nif->name[1];
    len += put_u(buf + len, nif->num);
    buf[len++] = '\n';

    len += put_field(buf + len, "mac");
    len += put_mac(buf + len, nif->hwaddr);
    buf[len++] = '\n';

    len += put_field(buf + len, "state");
    len += put_str(buf + len, net_bound ? "up\n" : "no address\n");

    len += put_field(buf + len, "address");
    len += put_ip4(buf + len, netif_ip4_addr(nif));
    buf[len++] = '\n';

    len += put_field(buf + len, "netmask");
    len += put_ip4(buf + len, netif_ip4_netmask(nif));
    buf[len++] = '\n';

    len += put_field(buf + len, "gateway");
    len += put_ip4(buf + len, netif_ip4_gw(nif));
    buf[len++] = '\n';

    len += put_field(buf + len, "mtu");
    len += put_u(buf + len, nif->mtu);
    buf[len++] = '\n';

    lwip_sys_unlock();

    uint64 rx, tx;
    net_e1000_counts(&rx, &tx);

    len += put_field(buf + len, "rx_frames");
    len += put_u(buf + len, rx);
    buf[len++] = '\n';

    len += put_field(buf + len, "tx_frames");
    len += put_u(buf + len, tx);
    buf[len++] = '\n';

    return len;
}

// Start the stack. Called from main() once processes exist.
void
netinit(void)
{
    if (net_started)
        return;
    // Before the check below, not after: the lock it initialises has to be
    // valid on a machine with no NIC too. Nothing can reach a wait there --
    // inet_new refuses while the stack is down -- but a lock whose validity
    // depends on that reasoning holding forever is not worth the two lines
    // saved.
    inet_init();
    if (!e1000_present()) {
        // Silent: a machine without an e1000 is not misconfigured, and this
        // runs on every boot.
        return;
    }
    net_started = 1;
    if (kthread_create(net_thread, "netd") < 0)
        cprintf("net: could not start the network thread\n");
}