nexoniarz/SchOS
nexoniarz/SchOS
Watch
1
0
Fork
You've already forked SchOS
 0
Code Issues Pull requests Projects Releases 1 Packages Wiki Activity Actions

hybrid: /dev/pci -- a driver can live outside the kernel now

Browse source 
docs/plan/hybrid.md mechanisms 2 and 4: MMIO and DMA to a process.

A process can enumerate the bus, claim a device exclusively, map its BARs and
get memory the device can be pointed at. Proven end to end against an e1000e
-- the exact device class we cannot drive and would want a foreign driver for:

    device 7: 8086:10d3 (network)
      claimed
      BAR0 at 0x81060000, 128 KB
      regs[0..3] = 0x00140261 0x00000000 0x00080283 0x00000000
      MMIO reaches the device
      DMA 8 KB at virtual 0x40001000, physical 0x3f8eb000

Those are the e1000e's CTRL and STATUS with full-duplex and link-up set, which
is how you tell a real mapping from one reading 0xFFFFFFFF off an unmapped
address. Claiming a device the kernel drives is refused -- two writers of one
register set looks like hardware that has started lying -- and everything a
process held is released when it exits, because a driver that crashed must not
keep its hardware away from its replacement.

mmap's offset is the BAR's physical address, checked against the BARs of
devices *this process has claimed*. Without that check the device is /dev/mem
with extra steps and a process could map the kernel's own memory. Mappings are
write-through: a cached write to a doorbell arrives whenever the cache feels
like it, which from a driver's side is indistinguishable from hardware that
ignores you.

The interface is about PCI devices, not about any driver model, and its first
users will be SchOS's own drivers when virtio-gpu is evicted. That ordering is
the design rather than an accident: an interface whose first consumers are
native drivers is a general mechanism something foreign can use later, instead
of a hole shaped like something foreign.

Also: PROT_* and MAP_* moved to include/posix.h. They were defined only in
sys_mem.c, so cmd/fbinfo carried a private copy and this wanted a third --
two copies of a number the kernel compares against, where a mismatch shows up
as a mapping with the wrong permissions rather than an error.

No IOMMU, so this isolates a driver against its own bugs and not against its
own DMA. The plan says so at length and it is still true.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2
This commit is contained in:
Nexoniarz 2026-09-13 15:34:28 +02:00
commit 24f79194ab
14 changed files with 678 additions and 11 deletions
Download patch file Download diff file Expand all files Collapse all files

17
include/posix.h
View file

@ -350,6 +350,23 @@ struct statfs {
#define FALLOC_FL_KEEP_SIZE 1
// poll(2) event bits (Linux values)
// mmap(2) protection and flags.
//
// These lived only in kernel/sys/sys_mem.c, so every userspace caller wrote
// its own copy -- cmd/fbinfo had one and cmd/pcitest wanted a third. Two
// private copies of a number the kernel compares against is a mismatch
// waiting to happen, and the symptom would be a mapping with the wrong
// permissions rather than an error.
#define PROT_NONE 0x0
#define PROT_READ 0x1
#define PROT_WRITE 0x2
#define PROT_EXEC 0x4
#define MAP_SHARED 0x01
#define MAP_PRIVATE 0x02
#define MAP_FIXED 0x10
#define MAP_ANONYMOUS 0x20
// waitpid() options. The kernel tests `options & 1`; this is that bit, named.
#define WNOHANG 0x001