Alpine's libinput, libseat, seatd, xf86-input-libinput and usbutils join the
image, and seatd runs from schinit. libinput lists the keyboard and pointer as
an ordinary user, Xorg now drives both through libinput, and a program linked
to libseat running as schos opens seat0 through seatd, is handed
/dev/input/event0 and reads its name through the descriptor.
Two kernel bugs stood in the way, and both would have stopped a Wayland
compositor too. The socket connect() queues for a listener was allocated with
its domain at zero, so sendmsg refused SCM_RIGHTS on the accepted end: a server
could receive descriptors and never send one. And sendmsg treated a control
buffer longer than its messages as an error, where Linux takes a following
header too short to be one as the end; seatd passes a zeroed CMSG_SPACE array
with one descriptor at the front.
Found with /proc/strace and a temporary kinfo in sendmsg's EINVAL sites.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EVRhxi9zpdW2uDUN4FVcao
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
udevd and a one-shot trigger run from schinit, 10-schos.conf no longer lists
event0/event1, and the docs say what udev covers and what it does not.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EVRhxi9zpdW2uDUN4FVcao
