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ldls: a network, in a process

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docs/plan/ldls.md L3a -- the class bridge, and the first of the three pieces
L3 turned out to be.

/dev/netdev is /dev/pci with the arrows reversed. That hands a device to a
process; this lets a process be one. The kernel side is netdev_ops and nothing
else -- transmit, receive, mac, link_up, the same four entries e1000
publishes -- so a process claims the device, supplies a MAC, and from then on
read() gives it frames the stack wants sent and write() hands it frames that
arrived.

cmd/netecho proves it and is deliberately not a driver: no hardware, none
claimed, every frame answered by the program itself. DHCP so the interface
gets an address at all, ARP so the stack can find it, ICMP so it can be
pinged. All built by hand from RFCs 826, 791, 792 and 2131.

    # netecho &
    netuser: ldls0 is a process now, 2:4c:44:4c:53:1
    netecho: I am 10.9.0.1 and will offer 10.9.0.2
    netecho: answered DHCP, offering an address

    # cat /proc/netif
    interface ldls0   driver netuser   address 10.9.0.2   gateway 10.9.0.1

    # ping 10.9.0.1 3
    netecho: answered an ARP
    netecho: answered a ping
    3 packets transmitted, 3 received, 0% packet loss

The interface got its address by DHCP from a process and then answered ping
from one. lwIP never learns that the thing behind netdev_ops is not a driver,
which is the whole property the bridge exists to have.

It dies the way it should, too. kill the process and link_up() answers false
immediately, so the stack refuses to send -- "ping: sendto: -5" -- rather than
swallowing packets into a driver that is not there. Start another and the
*same* interface comes back, keeping its address. That came free:
netuser_release_all() sits beside pciuser_release_all() in exit() for exactly
the same reason, and the reason is that a process holding a device is one that
may crash.

One thing the kernel needed: netinit() starts DHCP on the devices that exist
when it runs, so an interface created later -- which is how an LDLS-hosted
driver arrives -- would have come up with no address and no way to get one.
net_attach_late() fixes that, and lives in kernel/net/net.c because that is
the only file allowed to include lwIP's headers.

Recorded as not done, because it is not: this proves the bridge, not a driver.
Nothing in that test loads a module. That is why it was done first -- if ping
had not worked here the bridge would be wrong, and now a failure with a real
driver can only be the driver's side. L3b is the SchOS-side host, L3c is the
fifteen symbols for real, and L3 is the two joined.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2
This commit is contained in:
Nexoniarz 2026-09-14 08:31:06 +02:00
commit 2a441af3c6
14 changed files with 953 additions and 5 deletions
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31
kernel/net/net.c
View file

@ -177,6 +177,37 @@ htonl_u32(uint v)
return ntohl_u32(v);
}
// Attach an interface that appeared after boot.
//
// netinit() walks the devices that exist when it runs and starts DHCP on each.
// An interface created later -- by a process claiming /dev/netdev, which is
// how an LDLS-hosted driver arrives -- misses that entirely, and would come up
// with no address and no way to ever get one.
//
// It lives here rather than in kernel/dev/netuser.c because this is the only
// file allowed to include lwIP's headers; reaching into the stack from a
// device driver would put them on every kernel file's include path. See the
// note on /proc/netif in kernel/dev/procfs.c, which is the same rule.
int
net_attach_late(struct device *d)
{
int idx;
if (!net_ready)
return -1; // netinit() has not run; it will pick this up
lwip_sys_lock();
idx = net_eth_attach(d);
if (idx >= 0)
dhcp_start(net_eth_netif(idx));
lwip_sys_unlock();
if (idx >= 0)
cprintf("net: %s attached as interface %d, asking for an address\n",
d->name, idx);
return idx;
}
static void
net_thread(void)
{