Re: [libvirt] [PATCH] network: truncate bridges' dummy tap device names to IFNAMSIZ (15) chars

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).

- 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); + }