The AF_VSOCK protocol added in Linux 5.6 uses a 32 bit port number. For NBD we map this to simple URIs[1] like nbd+vsock://CID:PORT (where CID is a number that acts a bit like a hostname and PORT is a 32 bit port number). eg: nbd+vsock://1:1000000000/ would be port 10^9 on the loopback address VMADDR_CID_LOCAL (== 1). The problem is that libxml2 arbitrarily limits port numbers to 999,999,999. I don't see any support for this limit in RFC 3986 [2]. Here is the code: https://github.com/GNOME/libxml2/blob/46837d47d59c7b8c9bd1d08a6a717a90a7f... It doesn't even return an error, just truncates the port number. You can see the problem with the program [3] below. It seems like libxml2 chose to do this for convenience rather than correctness. I think it should accept port numbers at least up to signed int (the type used to store port numbers), and give an error if the port number overflows. Is there anything I'm missing or would a patch which implements that be acceptable? Also could the uri->port field be changed to unsigned int without breaking ABI? Rich. [1] https://github.com/NetworkBlockDevice/nbd/blob/master/doc/uri.md [2] https://tools.ietf.org/html/rfc3986#section-3.2.3 [3] $ cat port.c #include <stdio.h> #include <stdlib.h> #include <stdint.h> #include <inttypes.h> #include <libxml/uri.h> int main (int argc, char *argv[]) { xmlURIPtr uri = xmlParseURI (argv[1]); if (!uri) { fprintf (stderr, "xmlParseURI failed\n"); exit (EXIT_FAILURE); } printf ("%s => uri->port = %d\n", argv[1], uri->port); exit (EXIT_SUCCESS); } $ ./port nbd+vsock://1:1000 nbd+vsock://1:1000 => uri->port = 1000 $ ./port nbd+vsock://1:100000 nbd+vsock://1:100000 => uri->port = 100000 $ ./port nbd+vsock://1:10000000 nbd+vsock://1:10000000 => uri->port = 10000000 $ ./port nbd+vsock://1:1000000000 nbd+vsock://1:1000000000 => uri->port = 99999999 -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-top is 'top' for virtual machines. Tiny program with many powerful monitoring features, net stats, disk stats, logging, etc. http://people.redhat.com/~rjones/virt-top