[Qemu-devel] [PATCH 15/18] nbd: Implement NBD_OPT_GO on server

[Eric Blake]

NBD_OPT_EXPORT_NAME is lousy: it requires us to close the connection
rather than report an error.  Upstream NBD recently added NBD_OPT_GO
as the improved version of the option that does what we want, along
with NBD_OPT_INFO that returns the same information but does not
transition to transmission phase.

Signed-off-by: Eric Blake <address@hidden>
---
 nbd/server.c | 122 ++++++++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 109 insertions(+), 13 deletions(-)

diff --git a/nbd/server.c b/nbd/server.c
index 379df8c..e68e83c 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -233,17 +233,19 @@ static int nbd_negotiate_send_rep(QIOChannel *ioc, 
uint32_t type, uint32_t opt)
     return nbd_negotiate_send_rep_len(ioc, type, opt, 0);
 }

-/* Send an NBD_REP_SERVER reply to NBD_OPT_LIST, including payload.
+/* Send the common part of an NBD_REP_SERVER reply for the given option,
+ * and include extra_len in the advertised payload.
  * Return -errno to kill connection, 0 to continue negotiation */
-static int nbd_negotiate_send_rep_list(QIOChannel *ioc, NBDExport *exp)
+static int nbd_negotiate_send_rep_server(QIOChannel *ioc, NBDExport *exp,
+                                         uint32_t opt, uint32_t extra_len)
 {
     uint32_t len;
     int rc;

     TRACE("Advertising export name '%s'", exp->name ? exp->name : "");
     len = strlen(exp->name);
-    rc = nbd_negotiate_send_rep_len(ioc, NBD_REP_SERVER, NBD_OPT_LIST,
-                                    len + sizeof(len));
+    rc = nbd_negotiate_send_rep_len(ioc, NBD_REP_SERVER, opt,
+                                    len + sizeof(len) + extra_len);
     if (rc < 0) {
         return rc;
     }
@@ -261,6 +263,15 @@ static int nbd_negotiate_send_rep_list(QIOChannel *ioc, 
NBDExport *exp)
     return 0;
 }

+/* Send an NBD_REP_SERVER reply to NBD_OPT_LIST, including payload.
+ * Return -errno to kill connection, 0 to continue negotiation. */
+static int nbd_negotiate_send_rep_list(QIOChannel *ioc, NBDExport *exp)
+{
+    return nbd_negotiate_send_rep_server(ioc, exp, NBD_OPT_LIST, 0);
+}
+
+/* Send a sequence of replies to NBD_OPT_LIST.
+ * Return -errno to kill connection, 0 to continue negotiation. */
 static int nbd_negotiate_handle_list(NBDClient *client, uint32_t length)
 {
     NBDExport *exp;
@@ -283,6 +294,8 @@ static int nbd_negotiate_handle_list(NBDClient *client, 
uint32_t length)
     return nbd_negotiate_send_rep(client->ioc, NBD_REP_ACK, NBD_OPT_LIST);
 }

+/* Send a reply to NBD_OPT_EXPORT_NAME.
+ * Return -errno to kill connection, 0 to end negotiation. */
 static int nbd_negotiate_handle_export_name(NBDClient *client, uint32_t length)
 {
     int rc = -EINVAL;
@@ -318,6 +331,73 @@ fail:
 }


+/* Handle NBD_OPT_INFO and NBD_OPT_GO.
+ * Return -errno to kill connection, 0 if ready for next option, and 1
+ * to move into transmission phase.  */
+static int nbd_negotiate_handle_info(NBDClient *client, uint32_t length,
+                                     uint32_t opt, uint16_t myflags)
+{
+    int rc;
+    char name[NBD_MAX_NAME_SIZE + 1];
+    NBDExport *exp;
+    uint64_t size;
+    uint16_t flags;
+
+    /* Client sends:
+        [20 ..  xx]   export name (length bytes)
+     */
+    TRACE("Checking length");
+    if (length >= sizeof(name)) {
+        if (nbd_negotiate_drop_sync(client->ioc, length) != length) {
+            return -EIO;
+        }
+        return nbd_negotiate_send_rep(client->ioc, NBD_REP_ERR_INVALID, opt);
+    }
+    if (nbd_negotiate_read(client->ioc, name, length) != length) {
+        LOG("read failed");
+        return -EIO;
+    }
+    name[length] = '\0';
+
+    TRACE("Client requested info on export '%s'", name);
+
+    exp = nbd_export_find(name);
+    if (!exp) {
+        return nbd_negotiate_send_rep(client->ioc, NBD_REP_ERR_UNKNOWN, opt);
+    }
+
+    QEMU_BUILD_BUG_ON(NBD_FINAL_REPLY_SIZE != sizeof(size) + sizeof(flags));
+    rc = nbd_negotiate_send_rep_server(client->ioc, exp, opt,
+                                       NBD_FINAL_REPLY_SIZE);
+    if (rc < 0) {
+        return rc;
+    }
+
+    assert((exp->nbdflags & ~65535) == 0);
+    size = cpu_to_be64(exp->size);
+    flags = cpu_to_be16(exp->nbdflags | myflags);
+
+    if (nbd_negotiate_write(client->ioc, &size, sizeof(size)) !=
+        sizeof(size)) {
+        LOG("write failed");
+        return -EIO;
+    }
+    if (nbd_negotiate_write(client->ioc, &flags, sizeof(flags)) !=
+        sizeof(flags)) {
+        LOG("write failed");
+        return -EIO;
+    }
+
+    if (opt == NBD_OPT_GO) {
+        client->exp = exp;
+        QTAILQ_INSERT_TAIL(&client->exp->clients, client, next);
+        nbd_export_get(client->exp);
+        rc = 1;
+    }
+    return rc;
+}
+
+
 static QIOChannel *nbd_negotiate_handle_starttls(NBDClient *client,
                                                  uint32_t length)
 {
@@ -366,7 +446,10 @@ static QIOChannel *nbd_negotiate_handle_starttls(NBDClient 
*client,
 }


-static int nbd_negotiate_options(NBDClient *client)
+/* Loop over all client options, during fixed newstyle negotiation.
+ * Return -errno to kill connection, 0 on successful NBD_OPT_EXPORT_NAME,
+ * 1 on successful NBD_OPT_GO.  */
+static int nbd_negotiate_options(NBDClient *client, uint16_t myflags)
 {
     uint32_t flags;
     bool fixedNewstyle = false;
@@ -480,6 +563,16 @@ static int nbd_negotiate_options(NBDClient *client)
             case NBD_OPT_EXPORT_NAME:
                 return nbd_negotiate_handle_export_name(client, length);

+            case NBD_OPT_INFO:
+            case NBD_OPT_GO:
+                ret = nbd_negotiate_handle_info(client, length, clientflags,
+                                                myflags);
+                if (ret) {
+                    assert(ret < 0 || clientflags == NBD_OPT_GO);
+                    return ret;
+                }
+                break;
+
             case NBD_OPT_STARTTLS:
                 if (nbd_negotiate_drop_sync(client->ioc, length) != length) {
                     return -EIO;
@@ -584,18 +677,21 @@ static coroutine_fn int nbd_negotiate(NBDClientNewData 
*data)
             LOG("write failed");
             goto fail;
         }
-        rc = nbd_negotiate_options(client);
-        if (rc != 0) {
+        rc = nbd_negotiate_options(client, myflags);
+        if (rc < 0) {
             LOG("option negotiation failed");
             goto fail;
         }

-        stq_be_p(buf + 18, client->exp->size);
-        stw_be_p(buf + 26, client->exp->nbdflags | myflags);
-        len = client->no_zeroes ? 10 : sizeof(buf) - 18;
-        if (nbd_negotiate_write(client->ioc, buf + 18, len) != len) {
-            LOG("write failed");
-            goto fail;
+        if (!rc) {
+            /* If options ended with NBD_OPT_GO, we already sent this. */
+            stq_be_p(buf + 18, client->exp->size);
+            stw_be_p(buf + 26, client->exp->nbdflags | myflags);
+            len = client->no_zeroes ? 10 : sizeof(buf) - 18;
+            if (nbd_negotiate_write(client->ioc, buf + 18, len) != len) {
+                LOG("write failed");
+                goto fail;
+            }
         }
     }

-- 
2.5.5