Re: [Libguestfs] [libnbd PATCH] RFC: api: Add nbd_supports_vsock()

On 08/31/22 21:51, Eric Blake wrote: > Similar to nbd_supports_tls(), it is nice to know from a feature probe > whether we are likely to have VSOCK support before even trying more > expensive APIs like nbd_connect_uri("nbd+vsock://..."). > > --- > > https://bugzilla.redhat.com/show_bug.cgi?id=2069558 documents a case > where AF_VSOCK is compiled, but vsock still doesn't work because > vsock_loopback is not loaded. Should we make nbd_supports_vsock() > return true only when ALL aspects of vsock are known to be working? > --- > generator/API.ml | 25 ++++++++++++++++++++++--- > lib/handle.c | 17 +++++++++++++++++ > 2 files changed, 39 insertions(+), 3 deletions(-) I think the nbd_supports_tls(3) manual is a good example to follow here: "Returns true if libnbd was compiled with gnutls which is required to support TLS encryption, or false if not." It says "necessary" but does not say "sufficient", and the distinction is clear, too. So I think the present patch is good, but we should perhaps add a hint to longdesc about the necessary kernel modules. Rich always says that error reports and such should recommend actions for the user, and I think extending longdesc with kernel module hints should cover that. (Making nbd_supports_vsock() check for the kernel module, but *not* reporting it human-readably as the failure reason, would be too obscure IMO.)

So with the longdesc expansion: Acked-by: Laszlo Ersek <lersek(a)redhat.com&gt;