libnbd/0001-generator-Print-full-error-in-handle_reply_error.patch

From 9e51ca3dc11b4abe2e5145837ae80863fc300646 Mon Sep 17 00:00:00 2001
From: "Richard W.M. Jones" <rjones@redhat.com>
Date: Tue, 23 Jul 2024 17:22:12 +0100
Subject: [PATCH] generator: Print full error in handle_reply_error

Print the full error from the server during handshaking.  This
modifies the contract of handle_reply_error so it calls set_error,
which can be overridden by callers or ignored completely.

(cherry picked from commit cf49a49adc8abc8c917437db7461ed9956583877)
---
 generator/states-newstyle-opt-go.c           | 32 +--------
 generator/states-newstyle-opt-list.c         |  5 +-
 generator/states-newstyle-opt-meta-context.c |  8 +--
 generator/states-newstyle.c                  | 68 ++++++++++++++++++--
 4 files changed, 69 insertions(+), 44 deletions(-)

diff --git a/generator/states-newstyle-opt-go.c b/generator/states-newstyle-opt-go.c
index 5bc9a9ae..f6eb8afc 100644
--- a/generator/states-newstyle-opt-go.c
+++ b/generator/states-newstyle-opt-go.c
@@ -247,37 +247,9 @@ STATE_MACHINE {
       SET_NEXT_STATE (%.DEAD);
       return 0;
     }
-    /* Decode expected known errors into a nicer string */
-    switch (reply) {
-    case NBD_REP_ERR_UNSUP:
+    if (reply == NBD_REP_ERR_UNSUP)
       assert (h->opt_current == NBD_OPT_INFO);
-      set_error (ENOTSUP, "handshake: server lacks NBD_OPT_INFO support");
-      break;
-    case NBD_REP_ERR_POLICY:
-    case NBD_REP_ERR_PLATFORM:
-      set_error (0, "handshake: server policy prevents NBD_OPT_GO");
-      break;
-    case NBD_REP_ERR_INVALID:
-    case NBD_REP_ERR_TOO_BIG:
-      set_error (EINVAL, "handshake: server rejected NBD_OPT_GO as invalid");
-      break;
-    case NBD_REP_ERR_TLS_REQD:
-      set_error (ENOTSUP, "handshake: server requires TLS encryption first");
-      break;
-    case NBD_REP_ERR_UNKNOWN:
-      set_error (ENOENT, "handshake: server has no export named '%s'",
-                 h->export_name);
-      break;
-    case NBD_REP_ERR_SHUTDOWN:
-      set_error (ESHUTDOWN, "handshake: server is shutting down");
-      break;
-    case NBD_REP_ERR_BLOCK_SIZE_REQD:
-      set_error (EINVAL, "handshake: server requires specific block sizes");
-      break;
-    default:
-      set_error (0, "handshake: unknown reply from NBD_OPT_GO: 0x%" PRIx32,
-                 reply);
-    }
+
     nbd_internal_reset_size_and_flags (h);
     h->meta_valid = false;
     err = nbd_get_errno () ? : ENOTSUP;
diff --git a/generator/states-newstyle-opt-list.c b/generator/states-newstyle-opt-list.c
index cdd4676e..6605ee0a 100644
--- a/generator/states-newstyle-opt-list.c
+++ b/generator/states-newstyle-opt-list.c
@@ -127,9 +127,8 @@ STATE_MACHINE {
       SET_NEXT_STATE (%.DEAD);
       return 0;
     }
-    err = ENOTSUP;
-    set_error (err, "unexpected response, possibly the server does not "
-               "support listing exports");
+    debug (h, "unexpected response, possibly the server does not "
+           "support listing exports");
     break;
   }
 
diff --git a/generator/states-newstyle-opt-meta-context.c b/generator/states-newstyle-opt-meta-context.c
index 6f016e66..3945411e 100644
--- a/generator/states-newstyle-opt-meta-context.c
+++ b/generator/states-newstyle-opt-meta-context.c
@@ -270,12 +270,8 @@ STATE_MACHINE {
     }
 
     if (opt == h->opt_current) {
-      /* XXX Should we decode specific expected errors, like
-       * REP_ERR_UNKNOWN to ENOENT or REP_ERR_TOO_BIG to ERANGE?
-       */
-      err = ENOTSUP;
-      set_error (err, "unexpected response, possibly the server does not "
-                 "support meta contexts");
+      debug (h, "unexpected response, possibly the server does not "
+             "support meta contexts");
       CALL_CALLBACK (h->opt_cb.completion, &err);
       nbd_internal_free_option (h);
       SET_NEXT_STATE (%.NEGOTIATING);
diff --git a/generator/states-newstyle.c b/generator/states-newstyle.c
index 45893a8b..6c7cc45c 100644
--- a/generator/states-newstyle.c
+++ b/generator/states-newstyle.c
@@ -79,14 +79,18 @@ prepare_for_reply_payload (struct nbd_handle *h, uint32_t opt)
   return 0;
 }
 
-/* Check an unexpected server reply. If it is an error, log any
- * message from the server and return 0; otherwise, return -1.
+/* Check an unexpected server reply error.
+ *
+ * This calls set_error with a descriptive error message and returns
+ * 0.  Unless there is a further unexpected error while processing
+ * this error, in which case it calls set_error and returns -1.
  */
 static int
 handle_reply_error (struct nbd_handle *h)
 {
   uint32_t len;
   uint32_t reply;
+  char *msg = NULL;
 
   len = be32toh (h->sbuf.or.option_reply.replylen);
   reply = be32toh (h->sbuf.or.option_reply.reply);
@@ -101,9 +105,63 @@ handle_reply_error (struct nbd_handle *h)
     return -1;
   }
 
-  if (len > 0)
-    debug (h, "handshake: server error message: %.*s", (int)len,
-           h->sbuf.or.payload.err_msg);
+  /* Decode expected errors into a nicer string.
+   *
+   * XXX Note this string comes directly from the server, and most
+   * libnbd users simply print the error using 'fprintf'.  We really
+   * ought to quote this string somehow, but we don't have a useful
+   * function for that.
+   */
+  if (len > 0) {
+    if (asprintf (&msg, ": %.*s",
+                  (int)len, h->sbuf.or.payload.err_msg) == -1) {
+      set_error (errno, "asprintf");
+      return -1;
+    }
+  }
+
+  switch (reply) {
+  case NBD_REP_ERR_UNSUP:
+    set_error (ENOTSUP, "the operation is not supported by the server%s",
+               msg ? : "");
+      break;
+    case NBD_REP_ERR_POLICY:
+      set_error (0, "server policy prevents the operation%s",
+                 msg ? : "");
+      break;
+    case NBD_REP_ERR_PLATFORM:
+      set_error (0, "the operation is not supported by the server platform%s",
+                 msg ? : "");
+      break;
+    case NBD_REP_ERR_INVALID:
+      set_error (EINVAL, "the server rejected this operation as invalid%s",
+                 msg ? : "");
+      break;
+    case NBD_REP_ERR_TOO_BIG:
+      set_error (EINVAL, "the operation is too large to process%s",
+                 msg ? : "");
+      break;
+    case NBD_REP_ERR_TLS_REQD:
+      set_error (ENOTSUP, "the server requires TLS encryption first%s",
+                 msg ? : "");
+      break;
+    case NBD_REP_ERR_UNKNOWN:
+      set_error (ENOENT, "the server has no export named '%s'%s",
+                 h->export_name, msg ? : "");
+      break;
+    case NBD_REP_ERR_SHUTDOWN:
+      set_error (ESHUTDOWN, "the server is shutting down%s",
+                 msg ? : "");
+      break;
+    case NBD_REP_ERR_BLOCK_SIZE_REQD:
+      set_error (EINVAL, "the server requires specific block sizes%s",
+                 msg ? : "");
+      break;
+    default:
+      set_error (0, "handshake: unknown reply from the server: 0x%" PRIx32 "%s",
+                 reply, msg ? : "");
+    }
+  free (msg);
 
   return 0;
 }
-- 
2.43.0