NBD_OPT_EXPORT_NAME is lousy: it doesn't have any sane error reporting. Upstream NBD recently added NBD_OPT_GO as the improved version of the option that does what we want: it reports sane errors on failures (including when a server requires TLS but does not have NBD_OPT_GO!), and on success it provides at least as much info as NBD_OPT_EXPORT_NAME sends.
Signed-off-by: Eric Blake <ebl...@redhat.com> --- v3: revamp to match latest version of NBD protocol --- nbd/nbd-internal.h | 3 ++ nbd/client.c | 120 ++++++++++++++++++++++++++++++++++++++++++++++++++++- 2 files changed, 121 insertions(+), 2 deletions(-) diff --git a/nbd/nbd-internal.h b/nbd/nbd-internal.h index c597bb8..1935102 100644 --- a/nbd/nbd-internal.h +++ b/nbd/nbd-internal.h @@ -55,8 +55,11 @@ * 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 diff --git a/nbd/client.c b/nbd/client.c index 89fa2c3..dac4f29 100644 --- a/nbd/client.c +++ b/nbd/client.c @@ -222,6 +222,11 @@ static int nbd_handle_reply_err(QIOChannel *ioc, nbd_opt_reply *reply, reply->option); break; + case NBD_REP_ERR_UNKNOWN: + error_setg(errp, "Requested export not available for option %" PRIx32, + reply->option); + break; + case NBD_REP_ERR_SHUTDOWN: error_setg(errp, "Server shutting down before option %" PRIx32, reply->option); @@ -311,6 +316,103 @@ static int nbd_receive_list(QIOChannel *ioc, const char *want, Error **errp) } +/* 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 @size and @flags populated). */ +static int nbd_opt_go(QIOChannel *ioc, const char *wantname, + NbdExportInfo *info, Error **errp) +{ + nbd_opt_reply reply; + uint32_t len; + uint16_t type; + int error; + + /* 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("Attempting NBD_OPT_GO for export '%s'", wantname); + if (nbd_send_option_request(ioc, NBD_OPT_GO, -1, wantname, errp) < 0) { + return -1; + } + + TRACE("Reading export info"); + 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"); + return -1; + } + if (!info->flags) { + error_setg(errp, "broken server omitted NBD_INFO_EXPORT"); + return -1; + } + TRACE("export is good to go"); + return 1; + } + if (reply.type != NBD_REP_INFO) { + error_setg(errp, "unexpected reply type %" PRIx32 ", expected %x", + reply.type, NBD_REP_INFO); + return -1; + } + if (len < sizeof(type)) { + error_setg(errp, "NBD_REP_INFO length %" PRIu32 " is too short", + len); + return -1; + } + if (read_sync(ioc, &type, sizeof(type)) != sizeof(type)) { + error_setg(errp, "failed to read info type"); + 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); + return -1; + } + if (read_sync(ioc, &info->size, sizeof(info->size)) != + sizeof(info->size)) { + error_setg(errp, "failed to read info size"); + return -1; + } + be64_to_cpus(&info->size); + if (read_sync(ioc, &info->flags, sizeof(info->flags)) != + sizeof(info->flags)) { + error_setg(errp, "failed to read info flags"); + return -1; + } + be16_to_cpus(&info->flags); + TRACE("Size is %" PRIu64 ", export flags %" PRIx16, + info->size, info->flags); + break; + + default: + TRACE("ignoring unknown export info %" PRIu16, type); + if (drop_sync(ioc, len) != len) { + error_setg(errp, "Failed to read info payload"); + 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, @@ -515,11 +617,25 @@ 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; -- 2.5.5
