[dpdk-dev] [PATCH 2/3] stack: add lock-free support indication

[Stanislaw Kardach <kda@semihalf.com>]

Currently it is impossible to detect programatically whether lock-free
implementation of rte_stack is supported. One could check whether the
header guard for lock-free stubs is defined (_RTE_STACK_LF_STUBS_H_) but
that's an unstable implementation detail. Because of that currently all
lock-free ring creations silently succeed (as long as the stack header
is 16B long) which later leads to push and pop operations being NOPs.
The observable effect is that stack_lf_autotest fails on platforms not
supporting the lock-free. Instead it should just skip the lock-free test
altogether.

This commit adds a new errno value (ENOTSUP) that may be returned by
rte_stack_create() to indicate that a given combination of flags is not
supported on a current platform.
This is detected by checking a compile-time flag in the include logic in
rte_stack_lf.h which may be used by applications to check the lock-free
support at compile time.

Signed-off-by: Stanislaw Kardach <kda@semihalf.com>
Fixes: 7911ba0473e0 ("stack: enable lock-free implementation for aarch64")
Cc: phil.yang@arm.com
Cc: stable@dpdk.org
---
 doc/guides/rel_notes/release_21_05.rst | 4 ++++
 lib/librte_stack/rte_stack.c           | 4 +++-
 lib/librte_stack/rte_stack.h           | 1 +
 lib/librte_stack/rte_stack_lf.h        | 5 +++++
 4 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/doc/guides/rel_notes/release_21_05.rst b/doc/guides/rel_notes/release_21_05.rst
index 6f5858c8f..42ed60da8 100644
--- a/doc/guides/rel_notes/release_21_05.rst
+++ b/doc/guides/rel_notes/release_21_05.rst
@@ -166,6 +166,10 @@ API Changes
 * pci: The value ``PCI_ANY_ID`` is marked as deprecated
   and can be replaced with ``RTE_PCI_ANY_ID``.
 
+* Lock-free ``rte_stack`` no longer silently ignores push and pop when it's not
+  supported on the current platform. Instead ``rte_stack_create()`` fails and
+  ``rte_errno`` is set to ``ENOTSUP``.
+
 
 ABI Changes
 -----------
diff --git a/lib/librte_stack/rte_stack.c b/lib/librte_stack/rte_stack.c
index 8a51fba17..10d3b2eeb 100644
--- a/lib/librte_stack/rte_stack.c
+++ b/lib/librte_stack/rte_stack.c
@@ -64,9 +64,11 @@ rte_stack_create(const char *name, unsigned int count, int socket_id,
 
 #ifdef RTE_ARCH_64
 	RTE_BUILD_BUG_ON(sizeof(struct rte_stack_lf_head) != 16);
-#else
+#endif
+#if !defined(RTE_STACK_LF_SUPPORTED)
 	if (flags & RTE_STACK_F_LF) {
 		STACK_LOG_ERR("Lock-free stack is not supported on your platform\n");
+		rte_errno = ENOTSUP;
 		return NULL;
 	}
 #endif
diff --git a/lib/librte_stack/rte_stack.h b/lib/librte_stack/rte_stack.h
index b82c74e72..27640f87b 100644
--- a/lib/librte_stack/rte_stack.h
+++ b/lib/librte_stack/rte_stack.h
@@ -205,6 +205,7 @@ rte_stack_free_count(struct rte_stack *s)
  *    - EEXIST - a stack with the same name already exists
  *    - ENOMEM - insufficient memory to create the stack
  *    - ENAMETOOLONG - name size exceeds RTE_STACK_NAMESIZE
+ *    - ENOTSUP - platform does not support given flags combination.
  */
 struct rte_stack *
 rte_stack_create(const char *name, unsigned int count, int socket_id,
diff --git a/lib/librte_stack/rte_stack_lf.h b/lib/librte_stack/rte_stack_lf.h
index eb106e64e..f2b012cd0 100644
--- a/lib/librte_stack/rte_stack_lf.h
+++ b/lib/librte_stack/rte_stack_lf.h
@@ -13,6 +13,11 @@
 #else
 #include "rte_stack_lf_generic.h"
 #endif
+
+/**
+ * Indicates that RTE_STACK_F_LF is supported.
+ */
+#define RTE_STACK_LF_SUPPORTED
 #endif
 
 /**
-- 
2.27.0