While some applications may store metadata about packets in the packet
mbuf headroom, this is not a workable solution for packet metadata which
is either:
* larger than the headroom (or headroom is needed for adding pkt headers)
* needs to be shared or copied among packets
To support these use cases in applications, we reserve a general
"userdata" pointer field inside the second cache-line of the mbuf. This
is better than having the application store the pointer to the external
metadata in the packet headroom, as it saves an additional cache-line
from being used.
Apart from storing metadata, this field also provides a general 8-byte
scratch space inside the mbuf for any other application uses that are
applicable.
Changes in V2:
* made the userdata field always have 8-bytes available, even on 32-bit
Signed-off-by: Bruce Richardson <bruce.richardson at intel.com>
---
lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h | 6 ++++--
lib/librte_mbuf/rte_mbuf.h | 6 ++++++
2 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
b/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
index 25ed672..e548161 100644
--- a/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
+++ b/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
@@ -116,8 +116,10 @@ struct rte_kni_mbuf {
char pad2[2];
uint16_t data_len; /**< Amount of data in segment buffer. */
uint32_t pkt_len; /**< Total pkt len: sum of all segment
data_len. */
- char pad3[8];
- void *pool __attribute__((__aligned__(64)));
+
+ /* fields on second cache line */
+ char pad3[8] __attribute__((__aligned__(64)));
+ void *pool;
void *next;
};
diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index 8e27d2e..9e70d3b 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -172,6 +172,12 @@ struct rte_mbuf {
/* second cache line - fields only used in slow path or on TX */
MARKER cacheline1 __rte_cache_aligned;
+
+ union {
+ void *userdata; /**< Can be used for external metadata */
+ uint64_t udata64; /**< Allow 8-byte userdata on 32-bit */
+ };
+
struct rte_mempool *pool; /**< Pool from which mbuf was allocated. */
struct rte_mbuf *next; /**< Next segment of scattered packet. */
--
1.9.3
