nbd: Implement NBD_OPT_GO on client
NBD_OPT_EXPORT_NAME is lousy: per the NBD protocol, any failure
requires the server to close the connection rather than report an
error to us. Therefore, upstream NBD recently added NBD_OPT_GO as
the improved version of the option that does what we want [1]: it
reports sane errors on failures, and on success provides at least
as much info as NBD_OPT_EXPORT_NAME.
[1] https://github.com/NetworkBlockDevice/nbd/blob/extension-info/doc/proto.md
This is a first cut at use of the information types. Note that we
do not need to use NBD_OPT_INFO, and that use of NBD_OPT_GO means
we no longer have to use NBD_OPT_LIST to learn whether a server
requires TLS (this requires servers that gracefully handle unknown
NBD_OPT, many servers prior to qemu 2.5 were buggy, but I have patched
qemu, upstream nbd, and nbdkit in the meantime, in part because of
interoperability testing with this patch). We still fall back to
NBD_OPT_LIST when NBD_OPT_GO is not supported on the server, as it
is still one last chance for a nicer error message. Later patches
will use further info, like NBD_INFO_BLOCK_SIZE.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20170707203049.534-8-eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/nbd/trace-events b/nbd/trace-events
index 5230c61..bd09fab 100644
--- a/nbd/trace-events
+++ b/nbd/trace-events
@@ -3,6 +3,9 @@
nbd_send_option_request(uint32_t opt, const char *name, uint32_t len) "Sending option request %" PRIu32" (%s), len %" PRIu32
nbd_receive_option_reply(uint32_t option, const char *optname, uint32_t type, const char *typename, uint32_t length) "Received option reply %" PRIx32" (%s), type %" PRIx32" (%s), len %" PRIu32
nbd_reply_err_unsup(uint32_t option, const char *name) "server doesn't understand request %" PRIx32 " (%s), attempting fallback"
+nbd_opt_go_start(const char *name) "Attempting NBD_OPT_GO for export '%s'"
+nbd_opt_go_success(void) "Export is good to go"
+nbd_opt_go_info_unknown(int info, const char *name) "Ignoring unknown info %d (%s)"
nbd_receive_query_exports_start(const char *wantname) "Querying export list for '%s'"
nbd_receive_query_exports_success(const char *wantname) "Found desired export name '%s'"
nbd_receive_starttls_request(void) "Requesting TLS from server"
