* mbuf memory layout
@ 2022-02-01 18:16 fwefew 4t4tg
2022-02-01 18:19 ` Fwd: " fwefew 4t4tg
0 siblings, 1 reply; 2+ messages in thread
From: fwefew 4t4tg @ 2022-02-01 18:16 UTC (permalink / raw)
To: users
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I create a mempool thusly with 0 bytes private size and 1024 bytes data
room size:
rte_mempool *pool = rte_pktmbuf_pool_create("test", 1024, 0, 0, 1024, 0);
from which I allocate 1 mbuf.
which of the following three memory layouts best describes mbufs I allocate
from this
pool? I can't tell if it's the 2nd or 3rd one. I believe the first one is
wrong:
mbuf - RTE_PKTMBUF_HEADROOM not in data room
+--------------------------------+
|+------------------------------+|
||struct rte_mbuf ||
|+------------------------------+|
||RTE_PKTMBUF_HEADROOM bytes ||
|+------------------------------+| Data room starts here which will hold
||1024 bytes of data room size || L2/3/4 headers and actual payload. A
|+------------------------------+| pointer to the start of this field is
| . | given by rte_pktmbuf(mbuf, ...)
| . |
| . |
+--------------------------------+
mbuf - RTE_PKTMBUF_HEADROOM adds to data room size:
+--------------------------------+
|+------------------------------+|
||struct rte_mbuf ||
|+------------------------------+|Data room starts here which will hold
||1024 bytes + RTE_PKTMBUF_HEAD\||L2/3/4 headers and actual payload. A
||ROOM bytes ||pointer to the start of this field is
|| ||given by rte_pktmbuf(mbuf, ...)
|| ||
|+------------------------------+|
| . |
| . |
| . |
+--------------------------------+
mbuf - RTE_PKTMBUF_HEADROOM included in data room size
+--------------------------------+
|+------------------------------+|
||struct rte_mbuf ||
|+------------------------------+|Data room starts here which will hold
||1024 bytes of data room size ||L2/3/4 headers and actual payload. Since
|| ||data room size was >= RTE_PKTMBUF_HEADROOM
|| ||size the data room size of 1024 was valid
|+------------------------------+|and that's all that is reserved for the
| |data room
| |
| |
| |
+--------------------------------+
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^ permalink raw reply [flat|nested] 2+ messages in thread
* Fwd: mbuf memory layout
2022-02-01 18:16 mbuf memory layout fwefew 4t4tg
@ 2022-02-01 18:19 ` fwefew 4t4tg
0 siblings, 0 replies; 2+ messages in thread
From: fwefew 4t4tg @ 2022-02-01 18:19 UTC (permalink / raw)
To: users
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Darn it - typo: the pointer to the start of the data room in a mbuf was
incorrectly described earlier.
I should have written: rte_pktmbuf_mtod(mbuf, ....); // provide a pointer
to the start of the data room.
From: fwefew 4t4tg <7532yahoo@gmail.com>
Date: Tue, Feb 1, 2022 at 1:16 PM
Subject: mbuf memory layout
To: <users@dpdk.org>
I create a mempool thusly with 0 bytes private size and 1024 bytes data
room size:
rte_mempool *pool = rte_pktmbuf_pool_create("test", 1024, 0, 0, 1024, 0);
from which I allocate 1 mbuf.
which of the following three memory layouts best describes mbufs I allocate
from this
pool? I can't tell if it's the 2nd or 3rd one. I believe the first one is
wrong:
mbuf - RTE_PKTMBUF_HEADROOM not in data room
+--------------------------------+
|+------------------------------+|
||struct rte_mbuf ||
|+------------------------------+|
||RTE_PKTMBUF_HEADROOM bytes ||
|+------------------------------+| Data room starts here which will hold
||1024 bytes of data room size || L2/3/4 headers and actual payload. A
|+------------------------------+| pointer to the start of this field is
| . | given by rte_pktmbuf(mbuf, ...)
| . |
| . |
+--------------------------------+
mbuf - RTE_PKTMBUF_HEADROOM adds to data room size:
+--------------------------------+
|+------------------------------+|
||struct rte_mbuf ||
|+------------------------------+|Data room starts here which will hold
||1024 bytes + RTE_PKTMBUF_HEAD\||L2/3/4 headers and actual payload. A
||ROOM bytes ||pointer to the start of this field is
|| ||given by rte_pktmbuf(mbuf, ...)
|| ||
|+------------------------------+|
| . |
| . |
| . |
+--------------------------------+
mbuf - RTE_PKTMBUF_HEADROOM included in data room size
+--------------------------------+
|+------------------------------+|
||struct rte_mbuf ||
|+------------------------------+|Data room starts here which will hold
||1024 bytes of data room size ||L2/3/4 headers and actual payload. Since
|| ||data room size was >= RTE_PKTMBUF_HEADROOM
|| ||size the data room size of 1024 was valid
|+------------------------------+|and that's all that is reserved for the
| |data room
| |
| |
| |
+--------------------------------+
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