util: add virGetUNIXSocketPath helper

When receiving multiple socket FDs from systemd, it is critical to know
what socket address each corresponds to so we can setup the right
protocols on each.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

src/libvirt_private.syms

@@ -2980,6 +2980,7 @@ virGetListenFDs;
 virGetSelfLastChanged;
 virGetSystemPageSize;
 virGetSystemPageSizeKB;
+virGetUNIXSocketPath;
 virGetUnprivSGIOSysfsPath;
 virGetUserCacheDirectory;
 virGetUserConfigDirectory;

src/util/virutil.c

@@ -68,6 +68,10 @@
 # include <shlobj.h>
 #endif
 
+#ifdef HAVE_SYS_UN_H
+# include <sys/un.h>
+#endif
+
 #include "c-ctype.h"
 #include "mgetgroups.h"
 #include "virerror.h"
@@ -1978,6 +1982,47 @@ virGetListenFDs(void)
 
 #endif /* WIN32 */
 
+#ifdef HAVE_SYS_UN_H
+char *virGetUNIXSocketPath(int fd)
+{
+    struct sockaddr_storage ss = { 0 };
+    struct sockaddr_un *un = (struct sockaddr_un *)&ss;
+    socklen_t len = sizeof(ss);
+    char *path;
+
+    if (getsockname(fd, (struct sockaddr *)&ss, &len) < 0) {
+        virReportSystemError(errno, _("Unable to get address of FD %d"), fd);
+        return NULL;
+    }
+
+    if (ss.ss_family != AF_UNIX) {
+        virReportSystemError(EINVAL, _("FD %d is not a UNIX socket, has af=%d"),
+                             fd, ss.ss_family);
+        return NULL;
+    }
+
+    if (un->sun_path[0] == '\0')
+        un->sun_path[0] = '@';
+
+    if (VIR_ALLOC_N(path, sizeof(un->sun_path) + 1) < 0)
+        return NULL;
+
+    memcpy(path, un->sun_path, sizeof(un->sun_path));
+    path[sizeof(un->sun_path)] = '\0';
+    return path;
+}
+
+#else /* HAVE_SYS_UN_H */
+
+char *virGetUNIXSocketPath(int fd)
+{
+    virReportSystemError(ENOSYS, "%s",
+                         _("UNIX sockets not supported on this platform");
+    return NULL;
+}
+
+#endif /* HAVE_SYS_UN_H */
+
 #ifndef WIN32
 long virGetSystemPageSize(void)
 {

src/util/virutil.h

@@ -207,6 +207,7 @@ verify((int)VIR_TRISTATE_BOOL_NO == (int)VIR_TRISTATE_SWITCH_OFF);
 verify((int)VIR_TRISTATE_BOOL_ABSENT == (int)VIR_TRISTATE_SWITCH_ABSENT);
 
 unsigned int virGetListenFDs(void);
+char *virGetUNIXSocketPath(int fd);
 
 long virGetSystemPageSize(void) ATTRIBUTE_NOINLINE;
 long virGetSystemPageSizeKB(void) ATTRIBUTE_NOINLINE;