tree-wide: make format_ifname() or friends return negative errno on failure

Also,
- drop unnecessary +1 from buffer size, as IF_NAMESIZE or IFNAMSIZ
  includes the nul at the end.
- format_ifname() does not update buffer on failure,
- introduces format_ifname_alloc(), FORMAT_IFNAME(), and their friends.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/machine/machinectl.c b/src/machine/machinectl.c
index c3a2384f15..d18374dda0 100644
--- a/src/machine/machinectl.c
+++ b/src/machine/machinectl.c
@@ -557,9 +557,9 @@ static void print_machine_status_info(sd_bus *bus, MachineStatusInfo *i) {
                 fputs("\t   Iface:", stdout);
 
                 for (size_t c = 0; c < i->n_netif; c++) {
-                        char name[IF_NAMESIZE+1];
+                        char name[IF_NAMESIZE];
 
-                        if (format_ifname(i->netif[c], name)) {
+                        if (format_ifname(i->netif[c], name) >= 0) {
                                 fputc(' ', stdout);
                                 fputs(name, stdout);