X-Git-Url: http://git.droids-corp.org/?a=blobdiff_plain;f=doc%2Fguides%2Fprog_guide%2Fvhost_lib.rst;h=db921f922bd7f06f2b3011a52ab092fae5ab97f1;hb=3a66b2f90bcb08347626e26f206df07ebfa40058;hp=a86c07a6209501a1b9c51f1c53cff9fb5690e3d4;hpb=5c6c1480b3b01c2573cd52a85a01881aaa42b53f;p=dpdk.git

diff --git a/doc/guides/prog_guide/vhost_lib.rst b/doc/guides/prog_guide/vhost_lib.rst
index a86c07a620..db921f922b 100644
--- a/doc/guides/prog_guide/vhost_lib.rst
+++ b/doc/guides/prog_guide/vhost_lib.rst
@@ -63,7 +63,7 @@ The following is an overview of some key Vhost API functions:
       512).
 
     * zero copy is really good for VM2VM case. For iperf between two VMs, the
-      boost could be above 70% (when TSO is enableld).
+      boost could be above 70% (when TSO is enabled).
 
     * For zero copy in VM2NIC case, guest Tx used vring may be starved if the
       PMD driver consume the mbuf but not release them timely.
@@ -104,11 +104,6 @@ The following is an overview of some key Vhost API functions:
     from accessing memory the virtio device isn't allowed to, when the feature
     is negotiated and an IOMMU device is declared.
 
-    However, this feature enables vhost-user's reply-ack protocol feature,
-    which implementation is buggy in Qemu v2.7.0-v2.9.0 when doing multiqueue.
-    Enabling this flag with these Qemu version results in Qemu being blocked
-    when multiple queue pairs are declared.
-
   - ``RTE_VHOST_USER_POSTCOPY_SUPPORT``
 
     Postcopy live-migration support will be enabled when this flag is set.
@@ -117,6 +112,41 @@ The following is an overview of some key Vhost API functions:
     Enabling this flag should only be done when the calling application does
     not pre-fault the guest shared memory, otherwise migration would fail.
 
+  - ``RTE_VHOST_USER_LINEARBUF_SUPPORT``
+
+    Enabling this flag forces vhost dequeue function to only provide linear
+    pktmbuf (no multi-segmented pktmbuf).
+
+    The vhost library by default provides a single pktmbuf for given a
+    packet, but if for some reason the data doesn't fit into a single
+    pktmbuf (e.g., TSO is enabled), the library will allocate additional
+    pktmbufs from the same mempool and chain them together to create a
+    multi-segmented pktmbuf.
+
+    However, the vhost application needs to support multi-segmented format.
+    If the vhost application does not support that format and requires large
+    buffers to be dequeue, this flag should be enabled to force only linear
+    buffers (see RTE_VHOST_USER_EXTBUF_SUPPORT) or drop the packet.
+
+    It is disabled by default.
+
+  - ``RTE_VHOST_USER_EXTBUF_SUPPORT``
+
+    Enabling this flag allows vhost dequeue function to allocate and attach
+    an external buffer to a pktmbuf if the pkmbuf doesn't provide enough
+    space to store all data.
+
+    This is useful when the vhost application wants to support large packets
+    but doesn't want to increase the default mempool object size nor to
+    support multi-segmented mbufs (non-linear). In this case, a fresh buffer
+    is allocated using rte_malloc() which gets attached to a pktmbuf using
+    rte_pktmbuf_attach_extbuf().
+
+    See RTE_VHOST_USER_LINEARBUF_SUPPORT as well to disable multi-segmented
+    mbufs for application that doesn't support chained mbufs.
+
+    It is disabled by default.
+
 * ``rte_vhost_driver_set_features(path, features)``
 
   This function sets the feature bits the vhost-user driver supports. The