could fstat(1) show files in use by vnd(4)?

I had a XEN3_DOM0 kernel crash after doing "umount -f /build" (which I
did because "fstat /build" didn't find anything using that filesystem).

However there were several vnd(4) devices open by Xen domUs using files
on /build that I had completely forgotten about!

	[ 178445.6211804] fatal integer divide fault in supervisor mode
	[ 178445.6211804] trap type 8 code 0 rip 0xffffffff80936fb7 cs 0xe030 rflags 0x10246 cr2 0xffff9f82f9e21000 ilevel 0 rsp 0xffff9f8305c9ee00
	[ 178445.6211804] curlwp 0xffff9f8020cd81c0 pid 0.1268 lowest kstack 0xffff9f8305c9a2c0
	kernel: integer divide fault trap, code=0
	Stopped in pid 0.1268 (system) at       netbsd:vndthread+0x677: idivq   ffffffffffffff78(%rbp),%rax
	vndthread() at netbsd:vndthread+0x677
	ds          edf0
	es          0
	fs          81c0
	gs          800
	rdi         0
	rsi         6
	rbp         ffff9f8305c9eef0
	rbx         e0b0dc0
	rdx         0
	rcx         135
	rax         0
	r8          0
	r9          97a7c
	r10         ffff9f806119f040
	r11         fffffffe
	r12         0
	r13         800
	r14         ffff9f8021e3c800
	r15         0
	rip         ffffffff80936fb7    vndthread+0x677
	cs          e030
	rflags      10246
	rsp         ffff9f8305c9ee00
	ss          e02b
	netbsd:vndthread+0x677: idivq   ffffffffffffff78(%rbp),%rax
	db{4}>

After a reboot we can see the vnd(4) uses:

	# vndconfig -l
	vnd0: /build (/dev/mapper/vg0-build) inode 861956
	vnd1: /build (/dev/mapper/vg0-build) inode 861966
	vnd2: /build (/dev/mapper/vg0-build) inode 861953
	vnd3: not in use

So, might it be possible to have fstat show these somehow?  (perhaps
with the/a kernel thread identified as having them open)

Also, is this a crash that should be fixed, or is "umount -f" always a
Buyer-Beware operation with expected "undefined behaviour"?

--
					Greg A. Woods <[email protected]>

Kelowna, BC     +1 250 762-7675           RoboHack <[email protected]>
Planix, Inc. <[email protected]>     Avoncote Farms <[email protected]>

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