Richard W.M. Jones
2022-Sep-01 16:25 UTC
[Libguestfs] [libnbd PATCH v2 03/12] api: Allow nbd_opt_list_meta_context without SR
On Thu, Sep 01, 2022 at 11:21:38AM +0200, Laszlo Ersek wrote:> On 08/31/22 16:39, Eric Blake wrote: > > Upstream NBD clarified (see NBD commit 13a4e33a8) that since > > NBD_OPT_LIST_META_CONTEXT is stateless on the server side, it is > > acceptable (but not mandatory) for servers to accept it without the > > client having pre-negotiated structured replies. We aren't quite > > stateless on the client side yet - that will be fixed in a later patch > > to keep this one small and easier to test. The testsuite changes pass > > when using modern nbdkit; however, it skips[*] if we talk to an older > > server. But since the test also skips with our pre-patch behavior, > > it's not worth separating it into a separate patch. > > > > For more history, qemu-nbd prior to commit da24597d [v6.2] and nbdkit > > prior to commit c39cba73 [v1.27.3, also backported to 1.26.6] are > > servers that chose to reject NBD_OPT_LIST_META_CONTEXT without a prior > > NBD_OPT_STRUCTURED_REPLY. > > > > [*]It's easier to skip on server failure than to try and write an > > nbdkit patch to add yet another --config feature probe just to depend > > on new-enough nbdkit to gracefully probe in advance if the server > > should succeed. > > --- > > generator/states-newstyle-opt-meta-context.c | 1 - > > lib/opt.c | 6 +---- > > tests/opt-list-meta.c | 28 +++++++++++++++++--- > > 3 files changed, 25 insertions(+), 10 deletions(-) > > > > diff --git a/generator/states-newstyle-opt-meta-context.c b/generator/states-newstyle-opt-meta-context.c > > index a6a5271..5c65454 100644 > > --- a/generator/states-newstyle-opt-meta-context.c > > +++ b/generator/states-newstyle-opt-meta-context.c > > @@ -34,7 +34,6 @@ STATE_MACHINE { > > meta_vector_reset (&h->meta_contexts); > > if (h->opt_current == NBD_OPT_LIST_META_CONTEXT) { > > assert (h->opt_mode); > > - assert (h->structured_replies); > > assert (CALLBACK_IS_NOT_NULL (h->opt_cb.fn.context)); > > opt = h->opt_current; > > } > > Can we introduce some xfuncname pattern for these "state machine" C > files? The STATE_MACHINE hunk header is totally useless. I'd like > "NEWSTYLE.OPT_META_CONTEXT.START". :)It took me a while to work out what this means, but yes I agree. It seems the following should work but does not for me: .git/config add: [diff "nbdstate"] xfuncname = "^ [A-Z.]*:$" .git/info/attributes: generator/states-*.c diff=nbdstate Rich.> Regarding the code -- with the removal of the assertion from the LIST > branch, but preserving a similar check (albeit not an assert()) on the > SET branch, the comment covering *both* branches is now out of date: > > /* If the server doesn't support SRs then we must skip this group. > > > diff --git a/lib/opt.c b/lib/opt.c > > index e5802f4..d9114f4 100644 > > --- a/lib/opt.c > > +++ b/lib/opt.c > > @@ -1,5 +1,5 @@ > > /* NBD client library in userspace > > - * Copyright (C) 2020-2021 Red Hat Inc. > > + * Copyright (C) 2020-2022 Red Hat Inc. > > * > > * This library is free software; you can redistribute it and/or > > * modify it under the terms of the GNU Lesser General Public > > @@ -290,10 +290,6 @@ nbd_unlocked_aio_opt_list_meta_context (struct nbd_handle *h, > > set_error (ENOTSUP, "server is not using fixed newstyle protocol"); > > return -1; > > } > > - if (!h->structured_replies) { > > - set_error (ENOTSUP, "server lacks structured replies"); > > - return -1; > > - } > > > > assert (CALLBACK_IS_NULL (h->opt_cb.fn.context)); > > h->opt_cb.fn.context = *context; > > diff --git a/tests/opt-list-meta.c b/tests/opt-list-meta.c > > index 9ad8e37..ccf58fc 100644 > > --- a/tests/opt-list-meta.c > > +++ b/tests/opt-list-meta.c > > @@ -17,6 +17,7 @@ > > */ > > > > /* Test behavior of nbd_opt_list_meta_context. */ > > +/* See also unit test 240 in the various language ports. */ > > > > #include <config.h> > > > > @@ -164,7 +165,10 @@ main (int argc, char *argv[]) > > nbd_opt_abort (nbd); > > nbd_close (nbd); > > > > - /* Repeat but this time without structured replies. */ > > + /* Repeat but this time without structured replies. Below this point, > > + * it is not worth porting this part of the test to non-C languages > > + * because of the potential to skip the rest of the test. > > + */ > > nbd = nbd_create (); > > if (nbd == NULL || > > nbd_set_opt_mode (nbd, true) == -1 || > > @@ -174,15 +178,31 @@ main (int argc, char *argv[]) > > exit (EXIT_FAILURE); > > } > > > > - /* FIXME: For now, we reject this client-side, but it is overly strict. */ > > + /* Older servers don't permit this, but there is no reliable indicator > > + * of whether nbdkit is new enough, so just skip the rest of the test > > + * if the attempt fails (then read the logs to see that the skip was > > + * indeed caused by the server, and not an accidental client-side bug). > > + */ > > p = (struct progress) { .count = 0 }; > > r = nbd_opt_list_meta_context (nbd, > > (nbd_context_callback) { .callback = check, > > .user_data = &p}); > > - if (r != -1) { > > - fprintf (stderr, "not expecting command to succeed\n"); > > + if (r == -1) { > > + fprintf (stderr, "Skipping test; server probably too old for listing " > > + "without structured replies: %s\n", nbd_get_error ()); > > + exit (77); > > + } > > + if (r != p.count) { > > + fprintf (stderr, "inconsistent return value %d, expected %d\n", r, p.count); > > + exit (EXIT_FAILURE); > > + } > > + if (r < 1 || !p.seen) { > > + fprintf (stderr, "server did not reply with base:allocation\n"); > > exit (EXIT_FAILURE); > > } > > > > + nbd_opt_abort (nbd); > > + nbd_close (nbd); > > + > > exit (EXIT_SUCCESS); > > } > > > > On a tangent: why do we have nbd_opt_abort() separately from > nbd_close()? What further steps would be valid between the two? > > Reviewed-by: Laszlo Ersek <lersek at redhat.com> > _______________________________________________ > Libguestfs mailing list > Libguestfs at redhat.com > https://listman.redhat.com/mailman/listinfo/libguestfs-- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW
Eric Blake
2022-Sep-01 22:00 UTC
[Libguestfs] [libnbd PATCH v2 03/12] api: Allow nbd_opt_list_meta_context without SR
On Thu, Sep 01, 2022 at 05:25:55PM +0100, Richard W.M. Jones wrote:> > > > Can we introduce some xfuncname pattern for these "state machine" C > > files? The STATE_MACHINE hunk header is totally useless. I'd like > > "NEWSTYLE.OPT_META_CONTEXT.START". :) > > It took me a while to work out what this means, but yes I agree. > It seems the following should work but does not for me: > > .git/config add: > [diff "nbdstate"] > xfuncname = "^ [A-Z.]*:$"Probably also want _0-9 in that [].> > .git/info/attributes: > generator/states-*.c diff=nbdstateWe could also put it in .gitattributes (we've already done it for *.ml files, where we give the user the 'git config' command to run to take advantage of it). It's a shame it's not quite automatic from a fresh git checkout, but the idea should work if done right. Here's what I tested. In .gitattributes: # Use the following one-time config to get nicer diffs of generator state files: # git config diff.states.xfuncname '^([a-zA-Z_]| [A-Z._0-9]*:$)' generator/states-*.c diff=states then run that git config, then looking at 'git log -p generator/states-*.c', the diff for 30ee21f6 is a lot more legible, with lines like: +++ b/generator/states-reply-structured.c @@ -89,13 +89,8 @@ REPLY.STRUCTURED_REPLY.CHECK: } /* Skip an unexpected structured reply, including to an unknown cookie. */ - if (cmd == NULL || !h->structured_replies) { where the @@ line points to the right sub-state. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org