[libvirt] [PATCH 2/2] Bind to both IPv4 and v6 when checking port availability

[Daniel P. Berrange]

On Tue, Oct 01, 2013 at 11:01:37AM +0200, Ján Tomko wrote:
> If IPv6 is enabled on the host, bind to :: with IPV6_V6ONLY disabled
> to check for ports available on both IPv6 and IPv4.
> ---
>  src/util/virportallocator.c | 34 +++++++++++++++++++++++++++-------
>  1 file changed, 27 insertions(+), 7 deletions(-)
> 
> diff --git a/src/util/virportallocator.c b/src/util/virportallocator.c
> index 5b7ad41..246f6cd 100644
> --- a/src/util/virportallocator.c
> +++ b/src/util/virportallocator.c
> @@ -99,14 +99,25 @@ int virPortAllocatorAcquire(virPortAllocatorPtr pa,
>      int ret = -1;
>      size_t i;
>      int fd = -1;
> +    bool ipv6 = virHostHasIPv6();
>  
>      *port = 0;
>      virObjectLock(pa);
>  
>      for (i = pa->start; i <= pa->end && !*port; i++) {
> -        int reuse = 1;
> -        struct sockaddr_in addr;
> +        int reuse = 1, v6only = 0;
> +        struct sockaddr_in addr = {
> +            .sin_family = AF_INET,
> +            .sin_port = htons(i),
> +            .sin_addr.s_addr = htonl(INADDR_ANY)
> +        };
> +        struct sockaddr_in6 addr6 = {
> +            .sin6_family = AF_INET6,
> +            .sin6_port = htons(i),
> +            .sin6_addr = IN6ADDR_ANY_INIT
> +        };
>          bool used = false;
> +        int rc;
>  
>          if (virBitmapGetBit(pa->bitmap,
>                              i - pa->start, &used) < 0) {
> @@ -118,10 +129,7 @@ int virPortAllocatorAcquire(virPortAllocatorPtr pa,
>          if (used)
>              continue;
>  
> -        addr.sin_family = AF_INET;
> -        addr.sin_port = htons(i);
> -        addr.sin_addr.s_addr = htonl(INADDR_ANY);
> -        fd = socket(PF_INET, SOCK_STREAM, 0);
> +        fd = socket(ipv6 ? PF_INET6 : PF_INET, SOCK_STREAM, 0);
>          if (fd < 0) {
>              virReportSystemError(errno, "%s",
>                                   _("Unable to open test socket"));
> @@ -134,7 +142,19 @@ int virPortAllocatorAcquire(virPortAllocatorPtr pa,
>              goto cleanup;
>          }
>  
> -        if (bind(fd, (struct sockaddr*)&addr, sizeof(addr)) < 0) {
> +        if (ipv6 && setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, (void*)&v6only,
> +                               sizeof(v6only)) < 0) {
> +            virReportSystemError(errno, "%s",
> +                                 _("Unable to unset socket IPV6_V6ONLY flag"));
> +            goto cleanup;
> +        }
> +
> +        if (ipv6)
> +            rc = bind(fd, (struct sockaddr*)&addr6, sizeof(addr6));
> +        else
> +            rc = bind(fd, (struct sockaddr*)&addr, sizeof(addr));

IMHO you could write this code without needing to have any upfront check
for whether IPv6 is enabled. Set IPV6_V6ONLY == 1.

Then unconditionally try to bind separately on IPv4, and IPv6, and catch
the error you'd get back if either IPv4 or IPv6 were disabled on the
host.

Regards,
Daniel
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