Re: [Libguestfs] [nbdkit PATCH v2] main: Add option to disable SR advertisement

When we added support for .extents, we had nbdkit unconditionally support structured replies if the client requests them, and the plugin's .can_extents has no impact on what the server advertises. However, while the plugin API doesn't care whether the client requested SR, there are still integration situations where not advertising SR can be useful (such as comparison on what a client does with no block status vs. a block status that always reports allocated). We already have the command line options -o/-n for tweaking core server functionality; add --no-sr to the mix. In particular, doing this found that 'qemu-nbd --list' from qemu 4.2 is rather picky: it hangs up on a server that replies with NBD_REP_ERR_POLICY, rather than silently proceeding without SR support (at least libnbd is more tolerant). Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; --- Looks much different as a command line option instead of a hack to the noextents filter, but I like the result a lot better. I'm open to bike-shed opinions on the option name, or even if we want to emulate a tri-state option --protocol=[old|no-sr|new] (with -o and -n remaining synonyms for 2 of the 3 options for back-compat). I purposefully did not burn a short-option letter on the new option, as it is unlikely to be commonly needed. docs/nbdkit-plugin.pod | 5 +++- docs/nbdkit-protocol.pod | 21 ++++++++++++---- docs/nbdkit.pod | 12 ++++++++-- docs/synopsis.txt | 2 +- server/internal.h | 1 + server/options.h | 4 +++- server/main.c | 5 ++++ server/protocol-handshake-newstyle.c | 14 +++++++++++ tests/test-eflags.sh | 36 ++++++++++++++++++++++++++++ 9 files changed, 91 insertions(+), 9 deletions(-)