Commit 8ecaeae8 authored by Eric Blake's avatar Eric Blake Committed by Paolo Bonzini
Browse files

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: default avatarEric Blake <eblake@redhat.com>
Message-Id: <20170707203049.534-8-eblake@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent f37708f6

nbd/client.c

+124 −2
Original line number Diff line number Diff line
@@ -350,6 +350,114 @@ static int nbd_receive_list(QIOChannel *ioc, const char *want, bool *match, 
}





/* Returns -1 if NBD_OPT_GO proves the export @wantname cannot be

 * used, 0 if NBD_OPT_GO is unsupported (fall back to NBD_OPT_LIST and

 * NBD_OPT_EXPORT_NAME in that case), and > 0 if the export is good to

 * go (with @info populated). */

static int nbd_opt_go(QIOChannel *ioc, const char *wantname,

                      NBDExportInfo *info, Error **errp)

{

    nbd_opt_reply reply;

    uint32_t len = strlen(wantname);

    uint16_t type;

    int error;

    char *buf;



    /* The protocol requires that the server send NBD_INFO_EXPORT with

     * a non-zero flags (at least NBD_FLAG_HAS_FLAGS must be set); so

     * flags still 0 is a witness of a broken server. */

    info->flags = 0;



    trace_nbd_opt_go_start(wantname);

    buf = g_malloc(4 + len + 2 + 1);

    stl_be_p(buf, len);

    memcpy(buf + 4, wantname, len);

    /* No requests, live with whatever server sends */

    stw_be_p(buf + 4 + len, 0);

    if (nbd_send_option_request(ioc, NBD_OPT_GO, len + 6, buf, errp) < 0) {

        return -1;

    }



    while (1) {

        if (nbd_receive_option_reply(ioc, NBD_OPT_GO, &reply, errp) < 0) {

            return -1;

        }

        error = nbd_handle_reply_err(ioc, &reply, errp);

        if (error <= 0) {

            return error;

        }

        len = reply.length;



        if (reply.type == NBD_REP_ACK) {

            /* Server is done sending info and moved into transmission

               phase, but make sure it sent flags */

            if (len) {

                error_setg(errp, "server sent invalid NBD_REP_ACK");

                nbd_send_opt_abort(ioc);

                return -1;

            }

            if (!info->flags) {

                error_setg(errp, "broken server omitted NBD_INFO_EXPORT");

                nbd_send_opt_abort(ioc);

                return -1;

            }

            trace_nbd_opt_go_success();

            return 1;

        }

        if (reply.type != NBD_REP_INFO) {

            error_setg(errp, "unexpected reply type %" PRIx32 ", expected %x",

                       reply.type, NBD_REP_INFO);

            nbd_send_opt_abort(ioc);

            return -1;

        }

        if (len < sizeof(type)) {

            error_setg(errp, "NBD_REP_INFO length %" PRIu32 " is too short",

                       len);

            nbd_send_opt_abort(ioc);

            return -1;

        }

        if (nbd_read(ioc, &type, sizeof(type), errp) < 0) {

            error_prepend(errp, "failed to read info type");

            nbd_send_opt_abort(ioc);

            return -1;

        }

        len -= sizeof(type);

        be16_to_cpus(&type);

        switch (type) {

        case NBD_INFO_EXPORT:

            if (len != sizeof(info->size) + sizeof(info->flags)) {

                error_setg(errp, "remaining export info len %" PRIu32

                           " is unexpected size", len);

                nbd_send_opt_abort(ioc);

                return -1;

            }

            if (nbd_read(ioc, &info->size, sizeof(info->size), errp) < 0) {

                error_prepend(errp, "failed to read info size");

                nbd_send_opt_abort(ioc);

                return -1;

            }

            be64_to_cpus(&info->size);

            if (nbd_read(ioc, &info->flags, sizeof(info->flags), errp) < 0) {

                error_prepend(errp, "failed to read info flags");

                nbd_send_opt_abort(ioc);

                return -1;

            }

            be16_to_cpus(&info->flags);

            trace_nbd_receive_negotiate_size_flags(info->size, info->flags);

            break;



        default:

            trace_nbd_opt_go_info_unknown(type, nbd_info_lookup(type));

            if (nbd_drop(ioc, len, errp) < 0) {

                error_prepend(errp, "Failed to read info payload");

                nbd_send_opt_abort(ioc);

                return -1;

            }

            break;

        }

    }

}



/* Return -1 on failure, 0 if wantname is an available export. */

static int nbd_receive_query_exports(QIOChannel *ioc,

                                     const char *wantname,
@@ -531,11 +639,25 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, 
            name = "";

        }

        if (fixedNewStyle) {

            int result;



            /* Try NBD_OPT_GO first - if it works, we are done (it

             * also gives us a good message if the server requires

             * TLS).  If it is not available, fall back to

             * NBD_OPT_LIST for nicer error messages about a missing

             * export, then use NBD_OPT_EXPORT_NAME.  */

            result = nbd_opt_go(ioc, name, info, errp);

            if (result < 0) {

                goto fail;

            }

            if (result > 0) {

                return 0;

            }

            /* Check our desired export is present in the

             * server export list. Since NBD_OPT_EXPORT_NAME

             * cannot return an error message, running this

             * query gives us good error reporting if the

             * server required TLS

             * query gives us better error reporting if the

             * export name is not available.

             */

            if (nbd_receive_query_exports(ioc, name, errp) < 0) {

                goto fail;

nbd/nbd-internal.h

+3 −0
Original line number Diff line number Diff line
@@ -37,8 +37,11 @@ 
 * https://github.com/yoe/nbd/blob/master/doc/proto.md

 */



/* Size of all NBD_OPT_*, without payload */

#define NBD_REQUEST_SIZE        (4 + 2 + 2 + 8 + 8 + 4)

/* Size of all NBD_REP_* sent in answer to most NBD_OPT_*, without payload */

#define NBD_REPLY_SIZE          (4 + 4 + 8)



#define NBD_REQUEST_MAGIC       0x25609513

#define NBD_REPLY_MAGIC         0x67446698

#define NBD_OPTS_MAGIC          0x49484156454F5054LL

nbd/trace-events

+3 −0
Original line number Diff line number Diff line
@@ -3,6 +3,9 @@ nbd_unknown_error(int err) "Squashing unexpected error %d to EINVAL" 
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"