ACPIVMGENID(4) | Device Drivers Manual | ACPIVMGENID(4) |
acpivmgenid
— ACPI
Virtual Machine Generation ID
acpivmgenid* at acpi?
acpivmgenid
provides a generation ID for
virtual machines.
When starting two otherwise identical virtual machines, whether from the same clean image or by cloning snapshots or any other mechanism, the VM host may choose a different generation ID. Although this generation ID is not secret, it is incorporated into the entropy(7) pool (with a measure of zero entropy) so that the two virtual machines will produce independent random output.
If a live VM is cloned, the VM host may change the generation ID
in one or both of the clones and notify them through the
acpivmgenid
device. When this happens,
NetBSD will reseed system random number generators,
so that output of /dev/urandom and
getentropy(3) will be
independent in the two clones, and the
sysctl(7) variable
kern.entropy.epoch
will advance to notify
applications that they should reseed random number generators from the
system entropy pool.
The following sysctl(7) nodes are available:
hw.acpivmgenid
N.id
hw.acpivmgenid
N.paddr
arc4random(3), getentropy(3), rnd(4), entropy(7)
Virtual Machine Generation ID, http://go.microsoft.com/fwlink/?LinkId=260709, Microsoft, 2018-08-01.
Virtual Machine Generation ID Device, https://www.qemu.org/docs/master/specs/vmgenid.html, The QEMU Project Developers.
The acpivmgenid
driver first appeared in
NetBSD 10.1.
Currently there is no cheaper way to detect VM generation ID
changes than to query sysctl. (Applications deciding whether to reseed
random number generators should generally query
kern.entropy.epoch
, not
hw.acpivmgenid
N.id
.)
August 26, 2024 | NetBSD 10.99 |