lx: mkfifo blocks forever in Gentoo LX zone

[ismell]

SmartOS version: 20201118T153314Z

Install the gentoo lx zone from here: https://github.com/ismell/gentoo-lx-brand-image-builder

Then try the following:

mkfifo -m 600 /tmp/foo3

The command will block forever.

Using truss we can see the brand call that blocks:

# /native/usr/bin/truss mkfifo -m 600 /tmp/foo3
...

lwp_sigmask(SIG_SETMASK, 0x00000000, 0x00000000, 0x00000000, 0x00000000) = 0xFFBFFEFF [0xFFFFFFFF]
mmap(0x00000000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, 4294967295, 0) = 0x7FFFEF0D0000
getcontext(0x7FFFEF0D0040)
sysconfig(_CONFIG_STACK_PROT)			= 3
mmap(0x00000000, 262144, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_NORESERVE|MAP_ANON, 4294967295, 0) = 0x7FFFEF08F000
brand(147, 0x7FFFEF0CF000, 0x7FFFEF392E80, 0xFFFFFFFF, 0x00000000) = 0
getcontext(0x7FFFFFEFEE60)
brand(139, 0x7FFFFFEFEE60, 0x00000000, 0x00000000, 0x000003FF) = 0
mknod("/tmp/foo9", 010600, 0x00000000)		= 0
brand(130, 0x7FFFEF0CECA0, 0x00000085, 0x00000000, 0x00000000) = 0

[jasonbking]

Currently, mknod() in LX is a no-op (since most stuff shouldn't need to be talking to drivers directly). That's almost certainly part of the problem. I suspect it wouldn't be too difficult to allow FIFOs, and either ignore or error for other types of devices.

That LX mknod doesn't return an error today leads me to believe there's probably software out there that do try to create explicit device nodes that will fail if it returns an error, but otherwise seems to ignore it.