X-Git-Url: http://git.droids-corp.org/?a=blobdiff_plain;ds=sidebyside;f=doc%2Fguides%2Fprog_guide%2Fmbuf_lib.rst;h=2f190b40e43a0dc145aae80aae9159e534efede0;hb=6abd886826cf4c99dff83d3d2f5099e52937c147;hp=0d3223b0815354303ecce64d26e436480130cddc;hpb=d27a6261875d203424e93d7316a0e92852f367b5;p=dpdk.git

diff --git a/doc/guides/prog_guide/mbuf_lib.rst b/doc/guides/prog_guide/mbuf_lib.rst
index 0d3223b081..2f190b40e4 100644
--- a/doc/guides/prog_guide/mbuf_lib.rst
+++ b/doc/guides/prog_guide/mbuf_lib.rst
@@ -207,6 +207,29 @@ The list of flags and their precise meaning is described in the mbuf API
 documentation (rte_mbuf.h). Also refer to the testpmd source code
 (specifically the csumonly.c file) for details.
 
+Dynamic fields and flags
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+The size of the mbuf is constrained and limited;
+while the amount of metadata to save for each packet is quite unlimited.
+The most basic networking information already find their place
+in the existing mbuf fields and flags.
+
+If new features need to be added, the new fields and flags should fit
+in the "dynamic space", by registering some room in the mbuf structure:
+
+dynamic field
+   named area in the mbuf structure,
+   with a given size (at least 1 byte) and alignment constraint.
+
+dynamic flag
+   named bit in the mbuf structure,
+   stored in the field ``ol_flags``.
+
+The dynamic fields and flags are managed with the functions ``rte_mbuf_dyn*``.
+
+It is not possible to unregister fields or flags.
+
 .. _direct_indirect_buffer:
 
 Direct and Indirect Buffers
@@ -243,8 +266,8 @@ can be found in several of the sample applications, for example, the IPv4 Multic
 Debug
 -----
 
-In debug mode (CONFIG_RTE_MBUF_DEBUG is enabled),
-the functions of the mbuf library perform sanity checks before any operation (such as, buffer corruption, bad type, and so on).
+In debug mode, the functions of the mbuf library perform sanity checks before any operation (such as, buffer corruption,
+bad type, and so on).
 
 Use Cases
 ---------