On 04/13/2011 11:55 AM, Laine Stump wrote:
The solution is to shorten the part of the original name used to generate the tap device name. However, simply truncating it is insufficient, because the last few characters of an interface name are often a number used to indicate one of a list of several similar devices (for example, "verylongname123", "verylongname124", etc) and simple truncation would lead to duplicate names. So instead we take the first 8 characters of $bridgename ("verylong" in the example), add on the final 3 bytes ("123"), then add "-nic" (so "verylong123-nic"). Not pretty, but it is much more likely to generate a unique name, and is reproducible (unlike, say, a random number).
Should we also minimize the truncation by adding just "-n" instead of "-nic", so that there are fewer user strings being butchered? Or would that cause problems for existing users that already have bridge-nic and would now also have bridge-n?
- virAsprintf(&nicname, "%s-nic", brname); + if (strlen(brname) > (IFNAMSIZ - 5)) { + /* because the length of an ifname is limited to IFNAMSIZ-1 + * (usually 15), and we're adding 4 more characters, we must + * truncate the original name to 11 to fit. In order to catch + * a possible numeric ending (eg virbr0, virbr1, etc), we grab + * the first 8 and last 3 characters of the string. + */ + virAsprintf(&nicname, "%.*s%s-nic", + IFNAMSIZ - 8, /* space for last 3 chars + "-nic" + NULL */ + brname, brname + strlen(brname) - 3); + } else { + virAsprintf(&nicname, "%s-nic", brname); + }
ACK. -- Eric Blake eblake@redhat.com +1-801-349-2682 Libvirt virtualization library http://libvirt.org