sunrpc: Add comment defining gssd upcall API keywords

During review, it was found that the target, service, and srchost
keywords are easily conflated. Add an explainer.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
index 1943e11..2460759 100644 (file)
--- a/net/sunrpc/auth_gss/auth_gss.c
+++ b/net/sunrpc/auth_gss/auth_gss.c
@@ -461,12 +461,28 @@ static int gss_encode_v1_msg(struct gss_upcall_msg *gss_msg,
        buflen -= len;
        p += len;
        gss_msg->msg.len = len;
+
+       /*
+        * target= is a full service principal that names the remote
+        * identity that we are authenticating to.
+        */
        if (target_name) {
                len = scnprintf(p, buflen, "target=%s ", target_name);
                buflen -= len;
                p += len;
                gss_msg->msg.len += len;
        }
+
+       /*
+        * gssd uses service= and srchost= to select a matching key from
+        * the system's keytab to use as the source principal.
+        *
+        * service= is the service name part of the source principal,
+        * or "*" (meaning choose any).
+        *
+        * srchost= is the hostname part of the source principal. When
+        * not provided, gssd uses the local hostname.
+        */
        if (service_name) {
                char *c = strchr(service_name, '@');
 
@@ -482,6 +498,7 @@ static int gss_encode_v1_msg(struct gss_upcall_msg *gss_msg,
                p += len;
                gss_msg->msg.len += len;
        }
+
        if (mech->gm_upcall_enctypes) {
                len = scnprintf(p, buflen, "enctypes=%s ",
                                mech->gm_upcall_enctypes);