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PCI and USB devices in the /sys/devices tree, with uevents and USB hot-plug

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PCI devices live at /sys/devices/pci0000:00/<addr> and USB devices under the
xHCI controller that carries their bus, below that bus's root hub usbN;
/sys/bus/pci/devices and /sys/bus/usb/devices are symlinks into it, and every
device has its subsystem and driver links, which is how udev learns SUBSYSTEM
and DRIVER. Writing to a device's uevent now announces it with MODALIAS,
PCI_ID, PRODUCT and the rest, so udevadm trigger covers them, and the USB core
sends add when a device is attached and remove as it goes. The root hub is
announced when the controller comes up, before anything is plugged in.

Checked under QEMU: lspci and udevadm info through the links, udevadm monitor
showing the kernel and udev add event for device_add usb-kbd/usb-mouse and
the remove event for device_del, and a triggered add for usb1 and 1-5.

Known limits: the bus-to-controller mapping is a convention (bus N is the Nth
xHCI in PCI order); PCI bridges are not parents; USB interfaces and
/dev/bus/usb nodes are absent; busybox's lsusb reads /dev/bus/usb and prints
nothing.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EVRhxi9zpdW2uDUN4FVcao
This commit is contained in:
Nexoniarz 2026-10-26 15:51:28 +01:00
commit 8d836c66b2
8 changed files with 526 additions and 67 deletions
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9
kernel/dev/kdev.c
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@ -146,6 +146,13 @@ kdev_path(int i, char *buf, int cap)
static uint kseq;
// One counter for every uevent the kernel sends, whoever builds it.
uint
kdev_seqnum(void)
{
return ++kseq;
}
static int
put(char *b, int cap, int n, const char *s)
{
@ -190,7 +197,7 @@ vars(int i, char *buf, int cap, const char *action, int nl)
buf[n++] = sep;
if (action) {
n = put(buf, cap, n, "SEQNUM=");
n = putnum(buf, cap, n, ++kseq);
n = putnum(buf, cap, n, kdev_seqnum());
buf[n++] = sep;
}
if (k.devname[0]) {