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 concludes with the same data as NBD_OPT_EXPORT_NAME sends.
Signed-off-by: Eric Blake <ebl...@redhat.com> --- include/block/nbd.h | 1 + nbd/nbd-internal.h | 7 +++++ nbd/client.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++++++-- 3 files changed, 92 insertions(+), 2 deletions(-) diff --git a/include/block/nbd.h b/include/block/nbd.h index 35c0ea3..d261dbc 100644 --- a/include/block/nbd.h +++ b/include/block/nbd.h @@ -88,6 +88,7 @@ typedef struct nbd_reply nbd_reply; #define NBD_REP_ERR_POLICY ((UINT32_C(1) << 31) | 2) /* Server denied */ #define NBD_REP_ERR_INVALID ((UINT32_C(1) << 31) | 3) /* Invalid length. */ #define NBD_REP_ERR_TLS_REQD ((UINT32_C(1) << 31) | 5) /* TLS required */ +#define NBD_REP_ERR_UNKNOWN ((UINT32_C(1) << 31) | 6) /* Export unknown */ /* Request flags, sent from client to server during transmission phase */ #define NBD_CMD_FLAG_FUA (1 << 0) diff --git a/nbd/nbd-internal.h b/nbd/nbd-internal.h index b78d249..ddba1d0 100644 --- a/nbd/nbd-internal.h +++ b/nbd/nbd-internal.h @@ -55,8 +55,13 @@ * 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) +/* Size of reply to NBD_OPT_EXPORT_NAME, without trailing zeroes */ +#define NBD_FINAL_REPLY_SIZE (8 + 2) + #define NBD_REQUEST_MAGIC 0x25609513 #define NBD_REPLY_MAGIC 0x67446698 #define NBD_OPTS_MAGIC 0x49484156454F5054LL @@ -80,6 +85,8 @@ #define NBD_OPT_LIST (3) #define NBD_OPT_PEEK_EXPORT (4) #define NBD_OPT_STARTTLS (5) +#define NBD_OPT_INFO (6) +#define NBD_OPT_GO (7) /* NBD errors are based on errno numbers, so there is a 1:1 mapping, * but only a limited set of errno values is specified in the protocol. diff --git a/nbd/client.c b/nbd/client.c index 507ddc1..af17d4c 100644 --- a/nbd/client.c +++ b/nbd/client.c @@ -215,6 +215,11 @@ 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; + default: error_setg(errp, "Unknown error code when asking for option %" PRIx32, reply->option); @@ -299,6 +304,67 @@ static int nbd_receive_list(QIOChannel *ioc, const char *want, Error **errp) } +/* Returns -1 if NBD_OPT_GO proves the export 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 the server data at the same point as it would be right + * after sending NBD_OPT_EXPORT_NAME). */ +static int nbd_opt_go(QIOChannel *ioc, const char *wantname, Error **errp) +{ + nbd_opt_reply reply; + uint32_t len; + uint32_t namelen; + int error; + char buf[NBD_MAX_NAME_SIZE]; + + 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"); + 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_SERVER) { + error_setg(errp, "unexpected reply type %" PRIx32 ", expected %x", + reply.type, NBD_REP_SERVER); + return -1; + } + + if (len < sizeof(namelen) + NBD_FINAL_REPLY_SIZE || + len > sizeof(namelen) + sizeof(buf) + NBD_FINAL_REPLY_SIZE) { + error_setg(errp, "reply with %" PRIu32 " bytes is unexpected size", + len); + return -1; + } + + if (read_sync(ioc, &namelen, sizeof(namelen)) != sizeof(namelen)) { + error_setg(errp, "failed to read namelen"); + return -1; + } + be32_to_cpus(&namelen); + if (len != sizeof(namelen) + namelen + NBD_FINAL_REPLY_SIZE) { + error_setg(errp, "namelen %" PRIu32 " is unexpected size", + len); + return -1; + } + + if (read_sync(ioc, buf, namelen) != namelen) { + error_setg(errp, "failed to read name"); + return -1; + } + + TRACE("export is good to go"); + return 1; +} + /* Return -1 on failure, 0 if wantname is an available export. */ static int nbd_receive_query_exports(QIOChannel *ioc, const char *wantname, @@ -505,11 +571,26 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint32_t *flags, 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, errp); + if (result < 0) { + goto fail; + } + if (result > 0) { + zeroes = false; + goto success; + } /* 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; @@ -522,6 +603,7 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint32_t *flags, } /* Read the response */ + success: if (read_sync(ioc, &s, sizeof(s)) != sizeof(s)) { error_setg(errp, "Failed to read export length"); goto fail; -- 2.5.5
