[Libguestfs] [nbdkit PATCH] vddk: advise user on obscure thumbprint mismatch error condition

[Laszlo Ersek]

If the thumbprint parameter is wrong, it's only reported in
VixDiskLib_Open(), and then with the non-descript VIX_E_FAIL error code.
If the user typed or cut-and-pasted the thumbprint incorrectly, said
"Unkown error" message is not helpful for fixing the nbkit command line.
Hint at the thumbprint as the potential culprit.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1905772
Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---
 plugins/vddk/vddk-structs.h |  1 +
 plugins/vddk/vddk.c         | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/plugins/vddk/vddk-structs.h b/plugins/vddk/vddk-structs.h
index 799c4aecc5b8..4c7c6fe2e4fc 100644
--- a/plugins/vddk/vddk-structs.h
+++ b/plugins/vddk/vddk-structs.h
@@ -43,6 +43,7 @@
 
 typedef uint64_t VixError;
 #define VIX_OK 0
+#define VIX_E_FAIL 1
 #define VIX_E_NOT_SUPPORTED 6
 #define VIX_ASYNC 25000
 
diff --git a/plugins/vddk/vddk.c b/plugins/vddk/vddk.c
index 2ea071d641e6..dbd3fdbe09af 100644
--- a/plugins/vddk/vddk.c
+++ b/plugins/vddk/vddk.c
@@ -769,6 +769,26 @@ vddk_open (int readonly)
   VDDK_CALL_END (VixDiskLib_Open, 0);
   if (err != VIX_OK) {
     VDDK_ERROR (err, "VixDiskLib_Open: %s", filename);
+
+    /* Attempt to advise the user on the extremely helpful "Unknown error"
+     * result of VixDiskLib_Open().  The one reason we've seen for this error
+     * mode is a thumbprint mismatch (RHBZ#1905772).  Note that:
+     *
+     * (1) The thumbprint (as a part of "h->params") is passed to
+     *     VixDiskLib_ConnectEx() above, but the fingerprint mismatch is
+     *     detected only inside VixDiskLib_Open().
+     *
+     * (2) "thumb_print" may be NULL -- vddk_config_complete() is correct not to
+     *     require a non-NULL "thumb_print" for a remote connection; the sample
+     *     program "vixDiskLibSample.cpp" in vddk-7.0.3 explicitly permits
+     *     "-thumb" to be absent.
+     */
+    if (is_remote && err == VIX_E_FAIL)
+      nbdkit_error ("Please verify whether the \"thumbprint\" parameter (%s) "
+                    "matches the SHA1 fingerprint of the remote VMware "
+                    "server.  Refer to nbdkit-vddk-plugin(1) section "
+                    "\"THUMBPRINTS\" for details.",
+                    thumb_print == NULL ? "not specified" : thumb_print);
     goto err2;
   }
 

base-commit: 5007409b03486fa4b43526412d3db8de50325efd
-- 
2.19.1.3.g30247aa5d201