Re: [Libguestfs] [PATCH libnbd 2/2] api: New API for reading NBD protocol.
On 9/17/19 5:02 AM, Richard W.M. Jones wrote:
This commit adds a new API which can be used from the connected to
state to read back which NBD protocol (eg. oldstyle, newstyle-fixed)
we are using.
Somewhat of an overlap with my get_handshake_flags (as newstyle-fixed
corresponds to whether handshake_flags includes the FIXED_NEWSTYLE
flag), but I don't see the redundancy as an issue.
It was helpful to add a new state in newstyle negotiation
(%NEWSTYLE.FINISHED) so we can route all successful option
negotiations through a single path before moving to the %READY state,
allowing us to set h->protocol in one place.
---
+ "get_protocol", {
+ default_call with
+ args = []; ret = RStaticString;
+ permitted_states = [ Connected; Closed ];
+ shortdesc = "return the NBD protocol variant";
+ longdesc = "\
+Return the NBD protocol variant in use on the connection. At
+the moment this returns one of the strings C<\"oldstyle\">,
+C<\"newstyle\"> or C<\"newstyle-fixed\">. Other strings
might
+be returned in future. Most modern NBD servers use
C<\"newstyle-fixed\">.
s/in/in the/
+++ b/generator/states-newstyle.c
@@ -155,4 +155,13 @@ handle_reply_error (struct nbd_handle *h)
}
return 0;
+ NEWSTYLE.FINISHED:
+ if ((h->gflags & NBD_FLAG_FIXED_NEWSTYLE) == 0)
+ h->protocol = "newstyle";
+ else
+ h->protocol = "newstyle-fixed";
Should work whether this lands before or after my set_handshake_flags patch.
+++ b/lib/handle.c
@@ -315,3 +315,15 @@ nbd_unlocked_supports_uri (struct nbd_handle *h)
return 0;
#endif
}
+
+const char *
+nbd_unlocked_get_protocol (struct nbd_handle *h)
+{
+ /* I believe that if we reach the Connected or Closed permitted
+ * states, then the state machine must have set h->protocol. So if
+ * this assertion is hit then it indicates a bug in libnbd.
+ */
+ assert (h->protocol);
Sounds correct to me.
@@ -51,6 +54,14 @@ main (int argc, char *argv[])
exit (EXIT_FAILURE);
}
+ /* Even ancient versions of nbdkit only supported newstyle-fixed. */
+ s = nbd_get_protocol (nbd);
+ if (strcmp (s, "newstyle-fixed") != 0) {
+ fprintf (stderr,
+ "incorrect protocol \"%s\", expected
\"newstyle-fixed\"\n", s);
+ exit (EXIT_FAILURE);
+ }
With nbdkit 1.16 --mask-handshake and/or my patch for
nbd_set_handshake_flags, we can also provoke a test of "newstyle" as
output; looks like it's probably better for your patch to go in and me
to rebase mine on top of yours (since I was still working on writing
interop tests for mine).
ACK.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
Attachments:
- signature.asc (application/pgp-signature — 488 bytes)