patch 'ethdev: clarify null location case in xstats get' has been queued to stable release 20.11.6

[Xueming Li]

Hi,

FYI, your patch has been queued to stable release 20.11.6

Note it hasn't been pushed to http://dpdk.org/browse/dpdk-stable yet.
It will be pushed if I get no objections before 06/23/22. So please
shout if anyone has objections.

Also note that after the patch there's a diff of the upstream commit vs the
patch applied to the branch. This will indicate if there was any rebasing
needed to apply to the stable branch. If there were code changes for rebasing
(ie: not only metadata diffs), please double check that the rebase was
correctly done.

Queued patches are on a temporary branch at:
https://github.com/steevenlee/dpdk

This queued commit can be viewed at:
https://github.com/steevenlee/dpdk/commit/eb7b05b5de570be7a4bb62ec3e878df6f4a7811e

Thanks.

Xueming Li <xuemingl at nvidia.com>

---
>From eb7b05b5de570be7a4bb62ec3e878df6f4a7811e Mon Sep 17 00:00:00 2001
From: Chengwen Feng <fengchengwen at huawei.com>
Date: Fri, 13 May 2022 10:53:49 +0800
Subject: [PATCH] ethdev: clarify null location case in xstats get
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Cc: Xueming Li <xuemingl at nvidia.com>

[ upstream commit 485df8847a2c0ecf947a514f634b8180b725b827 ]

When xstats location is null in rte_eth_xstats_get() the return value
is not clearly specified.  Some PMDs (eg. hns3/ipn3ke/mvpp2/axgbe) return
zero while others return the required number of elements.

In this patch, special parameter combinations are restricted:
 1. highlight that xstats location may be null if and only if n is 0.
 2. amend n parameter description to specify that if n is lower than
    the required number of elements, the function returns the required
    number of elements.
 3. specify that if n is zero, the xstats must be NULL, the function
    returns the required number of elements (a duplicate which should
    help to not very attentive readers).

Add sanity check for null xstats and non-zero n case on API level to
make it unnecessary to care about it in drivers.

Fixes: ce757f5c9a4d ("ethdev: new method to retrieve extended statistics")

Signed-off-by: Chengwen Feng <fengchengwen at huawei.com>
Acked-by: Morten Brørup <mb at smartsharesystems.com>
Reviewed-by: Andrew Rybchenko <andrew.rybchenko at oktetlabs.ru>
---
 lib/librte_ethdev/rte_ethdev.c | 5 +++--
 lib/librte_ethdev/rte_ethdev.h | 6 +++++-
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/lib/librte_ethdev/rte_ethdev.c b/lib/librte_ethdev/rte_ethdev.c
index 24eb0d1197..028d16f99e 100644
--- a/lib/librte_ethdev/rte_ethdev.c
+++ b/lib/librte_ethdev/rte_ethdev.c
@@ -3170,7 +3170,8 @@ rte_eth_xstats_get(uint16_t port_id, struct rte_eth_xstat *xstats,
 	int ret;
 
 	RTE_ETH_VALID_PORTID_OR_ERR_RET(port_id, -ENODEV);
-
+	if (xstats == NULL && n > 0)
+		return -EINVAL;
 	dev = &rte_eth_devices[port_id];
 
 	nb_rxqs = RTE_MIN(dev->data->nb_rx_queues, RTE_ETHDEV_QUEUE_STAT_CNTRS);
@@ -3187,7 +3188,7 @@ rte_eth_xstats_get(uint16_t port_id, struct rte_eth_xstat *xstats,
 		 * xstats struct.
 		 */
 		xcount = (*dev->dev_ops->xstats_get)(dev,
-				     xstats ? xstats + count : NULL,
+				     (n > count) ? xstats + count : NULL,
 				     (n > count) ? n - count : 0);
 
 		if (xcount < 0)
diff --git a/lib/librte_ethdev/rte_ethdev.h b/lib/librte_ethdev/rte_ethdev.h
index 899f152a83..7da58d3fd1 100644
--- a/lib/librte_ethdev/rte_ethdev.h
+++ b/lib/librte_ethdev/rte_ethdev.h
@@ -2814,9 +2814,13 @@ int rte_eth_xstats_get_names(uint16_t port_id,
  * @param xstats
  *   A pointer to a table of structure of type *rte_eth_xstat*
  *   to be filled with device statistics ids and values.
- *   This parameter can be set to NULL if n is 0.
+ *   This parameter can be set to NULL if and only if n is 0.
  * @param n
  *   The size of the xstats array (number of elements).
+ *   If lower than the required number of elements, the function returns
+ *   the required number of elements.
+ *   If equal to zero, the xstats must be NULL, the function returns the
+ *   required number of elements.
  * @return
  *   - A positive value lower or equal to n: success. The return value
  *     is the number of entries filled in the stats table.
-- 
2.35.1

---
  Diff of the applied patch vs upstream commit (please double-check if non-empty:
---
--- -	2022-06-21 15:37:52.466881894 +0800
+++ 0070-ethdev-clarify-null-location-case-in-xstats-get.patch	2022-06-21 15:37:49.107784833 +0800
@@ -1 +1 @@
-From 485df8847a2c0ecf947a514f634b8180b725b827 Mon Sep 17 00:00:00 2001
+From eb7b05b5de570be7a4bb62ec3e878df6f4a7811e Mon Sep 17 00:00:00 2001
@@ -7,0 +8,3 @@
+Cc: Xueming Li <xuemingl at nvidia.com>
+
+[ upstream commit 485df8847a2c0ecf947a514f634b8180b725b827 ]
@@ -26 +28,0 @@
-Cc: stable at dpdk.org
@@ -32,9 +34,9 @@
- lib/ethdev/rte_ethdev.c | 4 +++-
- lib/ethdev/rte_ethdev.h | 6 +++++-
- 2 files changed, 8 insertions(+), 2 deletions(-)
-
-diff --git a/lib/ethdev/rte_ethdev.c b/lib/ethdev/rte_ethdev.c
-index 8520aec561..af55edb6b9 100644
---- a/lib/ethdev/rte_ethdev.c
-+++ b/lib/ethdev/rte_ethdev.c
-@@ -2973,6 +2973,8 @@ rte_eth_xstats_get(uint16_t port_id, struct rte_eth_xstat *xstats,
+ lib/librte_ethdev/rte_ethdev.c | 5 +++--
+ lib/librte_ethdev/rte_ethdev.h | 6 +++++-
+ 2 files changed, 8 insertions(+), 3 deletions(-)
+
+diff --git a/lib/librte_ethdev/rte_ethdev.c b/lib/librte_ethdev/rte_ethdev.c
+index 24eb0d1197..028d16f99e 100644
+--- a/lib/librte_ethdev/rte_ethdev.c
++++ b/lib/librte_ethdev/rte_ethdev.c
+@@ -3170,7 +3170,8 @@ rte_eth_xstats_get(uint16_t port_id, struct rte_eth_xstat *xstats,
@@ -43,0 +46 @@
+-
@@ -49 +52 @@
-@@ -2989,7 +2991,7 @@ rte_eth_xstats_get(uint16_t port_id, struct rte_eth_xstat *xstats,
+@@ -3187,7 +3188,7 @@ rte_eth_xstats_get(uint16_t port_id, struct rte_eth_xstat *xstats,
@@ -58,5 +61,5 @@
-diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h
-index 04cff8ee10..04225bba4d 100644
---- a/lib/ethdev/rte_ethdev.h
-+++ b/lib/ethdev/rte_ethdev.h
-@@ -3174,9 +3174,13 @@ int rte_eth_xstats_get_names(uint16_t port_id,
+diff --git a/lib/librte_ethdev/rte_ethdev.h b/lib/librte_ethdev/rte_ethdev.h
+index 899f152a83..7da58d3fd1 100644
+--- a/lib/librte_ethdev/rte_ethdev.h
++++ b/lib/librte_ethdev/rte_ethdev.h
+@@ -2814,9 +2814,13 @@ int rte_eth_xstats_get_names(uint16_t port_id,