Hi,
I'd like to query the host TAP interface name of a network backend via QMP,
especially when the TAP FD is passed to QEMU using SCM_RIGHTS
and then assigned to a backend through fd=.
In my current setup, retrieving this information externally requires
CAP_SYS_PTRACE. This gives the management process far more access
than needed and conflicts with the Landlock sandboxing I want to apply, due to
Landlock's ptrace restrictions [1].
QEMU already owns the FD, and tap_fd_get_ifname() can retrieve the name using
TUNGETIFF on Linux. For a TAP passed through fd=, x-query-
network currently reports the following (simplified):
{
"name": "hostnet0",
"type": "tap",
"info-str": "fd=42"
}
I'd like to obtain the actual interface name in a structured field, regardless
of how the TAP was created or passed to QEMU. For example:
{
"name": "hostnet0",
"type": "tap",
"info-str": "fd=42",
"data": {
"ifname": "vnet7"
}
}
Would extending x-query-network be the preferred approach? If so, would you
prefer a dedicated ifname field or a type-specific data object
selected by the existing type field?
Personally, I'd prefer an approach that is reasonably easy to backport
downstream to older QEMU releases. Since x-query-network is
relatively new, extending it would also require bringing that command to
releases which don't have it yet, potentially increasing the
backporting effort.
A type-specific data object could also accommodate additional TAP properties
later, such as multiqueue mode or vnet_hdr. However, those
are outside my current scope, I only need the interface name.
Is there an existing alternative I've missed?
Thanks!
[1] https://docs.kernel.org/userspace-api/landlock.html#ptrace-restrictions
