[Libguestfs] [nbdkit PATCH v2 1/5] nbd: Implement NBD_OPT_GO client request
Eric Blake
eblake at redhat.com
Thu Apr 25 18:01:42 UTC 2019
The NBD spec was recently patched (nbd.git commit 7827f3ae and
friends) to recommend NBD_OPT_GO for baseline interoperability, with
the aim of fewer servers and clients falling back to
NBD_OPT_EXPORT_NAME. And since nbdkit as server recently started
supporting NBD_OPT_GO (commit f7dd9799), our nbd client as plugin
should take advantage of it, which involves learning how to do option
haggling.
The use of option haggling is also a prerequisite to teaching the nbd
plugin about structured replies, which in turn will allow an
implementation of .extents.
Signed-off-by: Eric Blake <eblake at redhat.com>
---
plugins/nbd/nbd.c | 200 +++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 182 insertions(+), 18 deletions(-)
diff --git a/plugins/nbd/nbd.c b/plugins/nbd/nbd.c
index 71c1376..7f40035 100644
--- a/plugins/nbd/nbd.c
+++ b/plugins/nbd/nbd.c
@@ -1,5 +1,5 @@
/* nbdkit
- * Copyright (C) 2017-2018 Red Hat Inc.
+ * Copyright (C) 2017-2019 Red Hat Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
@@ -434,6 +434,157 @@ nbd_reply (struct handle *h, int fd)
return err ? -1 : 0;
}
+/* Receive response to @option into @reply, and consume any
+ payload. If @payload is non-NULL, caller must free *payload. Return
+ 0 on success, or -1 if communication to server is no longer
+ possible. */
+static int
+nbd_newstyle_recv_option_reply (struct handle *h, uint32_t option,
+ struct fixed_new_option_reply *reply,
+ void **payload)
+{
+ CLEANUP_FREE char *buffer = NULL;
+
+ if (payload)
+ *payload = NULL;
+ if (read_full (h->fd, reply, sizeof *reply)) {
+ nbdkit_error ("unable to read option reply: %m");
+ return -1;
+ }
+ reply->magic = be64toh (reply->magic);
+ reply->option = be32toh (reply->option);
+ reply->reply = be32toh (reply->reply);
+ reply->replylen = be32toh (reply->replylen);
+ if (reply->magic != NBD_REP_MAGIC || reply->option != option) {
+ nbdkit_error ("unexpected option reply");
+ return -1;
+ }
+ if (reply->replylen) {
+ if (reply->reply == NBD_REP_ACK) {
+ nbdkit_error ("NBD_REP_ACK should not have replylen %" PRId32,
+ reply->replylen);
+ return -1;
+ }
+ if (reply->replylen > 16 * 1024 * 1024) {
+ nbdkit_error ("option reply length is suspiciously large: %" PRId32,
+ reply->replylen);
+ return -1;
+ }
+ /* buffer is a string for NBD_REP_ERR_*; adding a NUL terminator
+ makes that string easier to use, without hurting other reply
+ types where buffer is not a string */
+ buffer = malloc (reply->replylen + 1);
+ if (!buffer) {
+ nbdkit_error ("malloc: %m");
+ return -1;
+ }
+ if (read_full (h->fd, buffer, reply->replylen)) {
+ nbdkit_error ("unable to read option reply payload: %m");
+ return -1;
+ }
+ buffer[reply->replylen] = '\0';
+ if (!payload)
+ nbdkit_debug ("ignoring option reply payload");
+ else {
+ *payload = buffer;
+ buffer = NULL;
+ }
+ }
+ return 0;
+}
+
+/* Attempt to negotiate structured reads, block status, and NBD_OPT_GO.
+ Return 1 if haggling completed, 0 if haggling failed but
+ NBD_OPT_EXPORT_NAME is still viable, or -1 on inability to connect. */
+static int
+nbd_newstyle_haggle (struct handle *h)
+{
+ struct new_option opt;
+ uint32_t exportnamelen = htobe32 (strlen (export));
+ /* For now, we make no NBD_INFO_* requests, relying on the server to
+ send its defaults. TODO: nbdkit should let plugins report block
+ sizes, at which point we should request NBD_INFO_BLOCK_SIZE and
+ obey any sizes set by server. */
+ uint16_t nrinfos = htobe16 (0);
+ struct fixed_new_option_reply reply;
+
+ /* TODO: structured reads, block status */
+
+ /* Try NBD_OPT_GO */
+ nbdkit_debug ("trying NBD_OPT_GO");
+ opt.version = htobe64 (NEW_VERSION);
+ opt.option = htobe32 (NBD_OPT_GO);
+ opt.optlen = htobe32 (sizeof exportnamelen + strlen (export) +
+ sizeof nrinfos);
+ if (write_full (h->fd, &opt, sizeof opt) ||
+ write_full (h->fd, &exportnamelen, sizeof exportnamelen) ||
+ write_full (h->fd, export, strlen (export)) ||
+ write_full (h->fd, &nrinfos, sizeof nrinfos)) {
+ nbdkit_error ("unable to request NBD_OPT_GO: %m");
+ return -1;
+ }
+ while (1) {
+ CLEANUP_FREE void *buffer;
+ struct fixed_new_option_reply_info_export *reply_export;
+ uint16_t info;
+
+ if (nbd_newstyle_recv_option_reply (h, NBD_OPT_GO, &reply, &buffer) < 0)
+ return -1;
+ switch (reply.reply) {
+ case NBD_REP_INFO:
+ /* Parse payload, but ignore all except NBD_INFO_EXPORT */
+ if (reply.replylen < 2) {
+ nbdkit_error ("NBD_REP_INFO reply too short");
+ return -1;
+ }
+ memcpy (&info, buffer, sizeof info);
+ info = be16toh (info);
+ switch (info) {
+ case NBD_INFO_EXPORT:
+ if (reply.replylen != sizeof *reply_export) {
+ nbdkit_error ("NBD_INFO_EXPORT reply wrong size");
+ return -1;
+ }
+ reply_export = buffer;
+ h->size = be64toh (reply_export->exportsize);
+ h->flags = be16toh (reply_export->eflags);
+ break;
+ default:
+ nbdkit_debug ("ignoring server info %d", info);
+ }
+ break;
+ case NBD_REP_ACK:
+ /* End of replies, valid if server already sent NBD_INFO_EXPORT,
+ observable since h->flags must contain NBD_FLAG_HAS_FLAGS */
+ assert (!buffer);
+ if (!h->flags) {
+ nbdkit_error ("server omitted NBD_INFO_EXPORT reply to NBD_OPT_GO");
+ return -1;
+ }
+ nbdkit_debug ("NBD_OPT_GO complete");
+ return 1;
+ case NBD_REP_ERR_UNSUP:
+ /* Special case this failure to fall back to NBD_OPT_EXPORT_NAME */
+ nbdkit_debug ("server lacks NBD_OPT_GO support");
+ return 0;
+ default:
+ /* Unexpected. Either the server sent a legitimate error or an
+ unexpected reply, but either way, we can't connect. */
+ if (NBD_REP_IS_ERR (reply.reply))
+ if (reply.replylen)
+ nbdkit_error ("server rejected NBD_OPT_GO with %s: %s",
+ name_of_nbd_rep (reply.reply), (char *) buffer);
+ else
+ nbdkit_error ("server rejected NBD_OPT_GO with %s",
+ name_of_nbd_rep (reply.reply));
+ else
+ nbdkit_error ("server used unexpected reply %s to NBD_OPT_GO",
+ name_of_nbd_rep (reply.reply));
+ return -1;
+ }
+ }
+}
+
/* Create the per-connection handle. */
static void *
nbd_open (int readonly)
@@ -473,6 +624,7 @@ nbd_open (int readonly)
}
version = be64toh (old.version);
if (version == OLD_VERSION) {
+ nbdkit_debug ("trying oldstyle connection");
if (read_full (h->fd,
(char *) &old + offsetof (struct old_handshake, exportsize),
sizeof old - offsetof (struct old_handshake, exportsize))) {
@@ -489,6 +641,7 @@ nbd_open (int readonly)
struct new_handshake_finish finish;
size_t expect;
+ nbdkit_debug ("trying newstyle connection");
if (read_full (h->fd, &gflags, sizeof gflags)) {
nbdkit_error ("unable to read global flags: %m");
goto err;
@@ -500,25 +653,36 @@ nbd_open (int readonly)
goto err;
}
- /* For now, we don't do any option haggling, but go straight into
- transmission phase */
- opt.version = htobe64 (NEW_VERSION);
- opt.option = htobe32 (NBD_OPT_EXPORT_NAME);
- opt.optlen = htobe32 (strlen (export));
- if (write_full (h->fd, &opt, sizeof opt) ||
- write_full (h->fd, export, strlen (export))) {
- nbdkit_error ("unable to request export '%s': %m", export);
- goto err;
+ /* Prefer NBD_OPT_GO if possible */
+ if (gflags & NBD_FLAG_FIXED_NEWSTYLE) {
+ int rc = nbd_newstyle_haggle (h);
+ if (rc < 0)
+ goto err;
+ if (!rc)
+ goto export_name;
}
- expect = sizeof finish;
- if (gflags & NBD_FLAG_NO_ZEROES)
- expect -= sizeof finish.zeroes;
- if (read_full (h->fd, &finish, expect)) {
- nbdkit_error ("unable to read new handshake: %m");
- goto err;
+ else {
+ export_name:
+ /* Option haggling untried or failed, use older NBD_OPT_EXPORT_NAME */
+ nbdkit_debug ("trying NBD_OPT_EXPORT_NAME");
+ opt.version = htobe64 (NEW_VERSION);
+ opt.option = htobe32 (NBD_OPT_EXPORT_NAME);
+ opt.optlen = htobe32 (strlen (export));
+ if (write_full (h->fd, &opt, sizeof opt) ||
+ write_full (h->fd, export, strlen (export))) {
+ nbdkit_error ("unable to request export '%s': %m", export);
+ goto err;
+ }
+ expect = sizeof finish;
+ if (gflags & NBD_FLAG_NO_ZEROES)
+ expect -= sizeof finish.zeroes;
+ if (read_full (h->fd, &finish, expect)) {
+ nbdkit_error ("unable to read new handshake: %m");
+ goto err;
+ }
+ h->size = be64toh (finish.exportsize);
+ h->flags = be16toh (finish.eflags);
}
- h->size = be64toh (finish.exportsize);
- h->flags = be16toh (finish.eflags);
}
else {
nbdkit_error ("unexpected version %#" PRIx64, version);
--
2.20.1
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