Re: [Libguestfs] [PATCH nbdkit] server: Add nbdkit_export_name() to allow export name to be read.

This allows plugins (or filters) to read the export name which was passed to the server from the client. UNFINISHED: - Needs tests --- TODO | 8 ++++++ docs/nbdkit-plugin.pod | 39 ++++++++++++++++++++++++++++ server/connections.c | 1 + server/internal.h | 1 + server/protocol-handshake-newstyle.c | 30 ++++++++++++--------- server/public.c | 10 +++++++ 6 files changed, 77 insertions(+), 12 deletions(-) diff --git a/TODO b/TODO index 49b60b1..2468d74 100644 --- a/TODO +++ b/TODO @@ -62,6 +62,12 @@ General ideas for improvements and also look at the implementation of the -swap option in nbd-client. +* Clients should be able to list export names supported by plugins. + Current behaviour is not really correct: We only list the -e + parameter from the command line, which is different from the export + name(s) that a plugin might want to support. Probably we should + deprecate the -e option entirely since it does nothing useful.

+++ b/docs/nbdkit-plugin.pod @@ -362,6 +362,45 @@ requested, or -1 after calling C<nbdkit_error> if there is no point in continuing the current command. Attempts to sleep more than C<INT_MAX> seconds are treated as an error. +=head1 EXPORT NAME + +If the client negotiated an NBD export name with nbdkit then plugins +may read this from any connected callbacks. Nbdkit's normal behaviour +is to accept any export name passed by the client, log it in debug +output, but otherwise ignore it. By using C<nbdkit_export_name> +plugins may choose to filter by export name or serve different +content.

+ +=head2 C<nbdkit_export_name> + + const char *nbdkit_export_name (void); + +Return the optional NBD export name if one was negotiated with the +current client (this uses thread-local magic so no parameter is +required). The returned string is only valid while the client is +connected, so if you need to store it in the plugin you must copy it. + +The export name is a free-form text string, it is not necessarily a +path or filename and it does not need to begin with a C<'/'> +character. The NBD protocol describes the empty string (C<"">) as a +representing a "default export" or to be used in cases where the +export name does not make sense. + +This may return C<NULL> which does I<not> indicate an error: + +=over 4 + +=item * + +It only returns the export name when there is a connected client. + +=item * + +If the server is using the oldstyle protocol the client does not send +an export name.

+++ b/server/protocol-handshake-newstyle.c @@ -274,11 +274,17 @@ negotiate_handshake_newstyle_options (struct connection *conn) if (conn_recv_full (conn, data, optlen, "read: %s: %m", name_of_nbd_opt (option)) == -1) return -1; - /* Apart from printing it, ignore the export name. */ + /* Print the export name and save it in the connection. */ data[optlen] = '\0'; - debug ("newstyle negotiation: %s: " - "client requested export '%s' (ignored)", + debug ("newstyle negotiation: %s: client requested export '%s'", name_of_nbd_opt (option), data); + free (conn->exportname); + conn->exportname = malloc (optlen+1); + if (conn->exportname == NULL) { + nbdkit_error ("malloc: %m"); + return -1; + } + memcpy (conn->exportname, data, optlen+1);