[dpdk-dev] [PATCH v2 7/9] eal: add lcore init callbacks

[David Marchand <david.marchand@redhat.com>]

DPDK components and applications can have their say when a new lcore is
initialized. For this, they can register a callback for initializing and
releasing their private data.

Signed-off-by: David Marchand <david.marchand@redhat.com>
---
Changes since v1:
- added unit test (since missing some coverage, for v3),
- preferred callback and removed mention of notification,

---
 app/test/test_lcores.c                   |  95 ++++++++++++++++
 lib/librte_eal/common/eal_common_lcore.c | 139 ++++++++++++++++++++++-
 lib/librte_eal/common/eal_private.h      |   3 +-
 lib/librte_eal/include/rte_lcore.h       |  68 +++++++++++
 lib/librte_eal/rte_eal_version.map       |   2 +
 5 files changed, 301 insertions(+), 6 deletions(-)

diff --git a/app/test/test_lcores.c b/app/test/test_lcores.c
index 155b255b94..cf2439f71d 100644
--- a/app/test/test_lcores.c
+++ b/app/test/test_lcores.c
@@ -5,6 +5,7 @@
 #include <pthread.h>
 #include <string.h>
 
+#include <rte_common.h>
 #include <rte_lcore.h>
 
 #include "test.h"
@@ -113,6 +114,95 @@ test_non_eal_lcores(unsigned int eal_threads_count)
 	return ret;
 }
 
+struct limit_lcore_context {
+	unsigned int init;
+	unsigned int max;
+	unsigned int uninit;
+};
+static int
+limit_lcores_init(unsigned int lcore_id __rte_unused, void *arg)
+{
+	struct limit_lcore_context *l = arg;
+
+	l->init++;
+	if (l->init > l->max)
+		return -1;
+	return 0;
+}
+static void
+limit_lcores_uninit(unsigned int lcore_id __rte_unused, void *arg)
+{
+	struct limit_lcore_context *l = arg;
+
+	l->uninit++;
+}
+
+static int
+test_lcores_callback(unsigned int eal_threads_count)
+{
+	struct limit_lcore_context l;
+	void *handle;
+
+	/* Refuse last lcore => callback register error. */
+	memset(&l, 0, sizeof(l));
+	l.max = eal_threads_count - 1;
+	handle = rte_lcore_callback_register("limit", limit_lcores_init,
+		limit_lcores_uninit, &l);
+	if (handle != NULL) {
+		printf("lcore callback register should have failed\n");
+		goto error;
+	}
+	/* Refusal happens at the n th call to the init callback.
+	 * Besides, n - 1 were accepted, so we expect as many uninit calls when
+	 * the rollback happens.
+	 */
+	if (l.init != eal_threads_count) {
+		printf("lcore init calls failed: expected %u, got %u\n",
+			eal_threads_count, l.init);
+		goto error;
+	}
+	if (l.uninit != eal_threads_count - 1) {
+		printf("lcore uninit calls failed: expected %u, got %u\n",
+			eal_threads_count - 1, l.uninit);
+		goto error;
+	}
+
+	/* Accept all lcore and unregister. */
+	memset(&l, 0, sizeof(l));
+	l.max = eal_threads_count;
+	handle = rte_lcore_callback_register("limit", limit_lcores_init,
+		limit_lcores_uninit, &l);
+	if (handle == NULL) {
+		printf("lcore callback register failed\n");
+		goto error;
+	}
+	if (l.uninit != 0) {
+		printf("lcore uninit got called %u times during register\n",
+			l.uninit);
+		goto error;
+	}
+	rte_lcore_callback_unregister(handle);
+	handle = NULL;
+	if (l.init != eal_threads_count) {
+		printf("lcore init got called %u times during unregister (expected %u)\n",
+			l.init, eal_threads_count);
+		goto error;
+	}
+	if (l.uninit != eal_threads_count) {
+		printf("lcore uninit calls failed: expected %u, got %u\n",
+			eal_threads_count, l.uninit);
+		goto error;
+	}
+
+	return 0;
+
+error:
+	if (handle != NULL)
+		rte_lcore_callback_unregister(handle);
+
+	return -1;
+}
+
 static int
 test_lcores(void)
 {
@@ -133,6 +223,11 @@ test_lcores(void)
 	if (test_non_eal_lcores(eal_threads_count) < 0)
 		return TEST_FAILED;
 
+	if (test_lcores_callback(eal_threads_count) < 0)
+		return TEST_FAILED;
+
+	/* FIXME: missing a test on callback + registering non-EAL threads */
+
 	return TEST_SUCCESS;
 }
 
diff --git a/lib/librte_eal/common/eal_common_lcore.c b/lib/librte_eal/common/eal_common_lcore.c
index 7db05428e7..5140026b6c 100644
--- a/lib/librte_eal/common/eal_common_lcore.c
+++ b/lib/librte_eal/common/eal_common_lcore.c
@@ -223,11 +223,114 @@ rte_socket_id_by_idx(unsigned int idx)
 }
 
 static rte_spinlock_t lcore_lock = RTE_SPINLOCK_INITIALIZER;
+struct lcore_callback {
+	TAILQ_ENTRY(lcore_callback) next;
+	char *name;
+	rte_lcore_init_cb init;
+	rte_lcore_uninit_cb uninit;
+	void *arg;
+};
+static TAILQ_HEAD(lcore_callbacks_head, lcore_callback) lcore_callbacks =
+	TAILQ_HEAD_INITIALIZER(lcore_callbacks);
+
+static int
+callback_init(struct lcore_callback *callback, unsigned int lcore_id)
+{
+	if (callback->init == NULL)
+		return 0;
+	RTE_LOG(DEBUG, EAL, "Call init for lcore callback %s, lcore_id %u\n",
+		callback->name, lcore_id);
+	return callback->init(lcore_id, callback->arg);
+}
+
+static void
+callback_uninit(struct lcore_callback *callback, unsigned int lcore_id)
+{
+	if (callback->uninit == NULL)
+		return;
+	RTE_LOG(DEBUG, EAL, "Call uninit for lcore callback %s, lcore_id %u\n",
+		callback->name, lcore_id);
+	callback->uninit(lcore_id, callback->arg);
+}
+
+void *
+rte_lcore_callback_register(const char *name, rte_lcore_init_cb init,
+	rte_lcore_uninit_cb uninit, void *arg)
+{
+	struct rte_config *cfg = rte_eal_get_configuration();
+	struct lcore_callback *callback;
+	unsigned int lcore_id;
+
+	callback = calloc(1, sizeof(*callback));
+	if (callback == NULL)
+		return NULL;
+	if (asprintf(&callback->name, "%s-%p", name, arg) == -1) {
+		free(callback);
+		return NULL;
+	}
+	callback->init = init;
+	callback->uninit = uninit;
+	callback->arg = arg;
+	rte_spinlock_lock(&lcore_lock);
+	if (callback->init == NULL)
+		goto no_init;
+	for (lcore_id = 0; lcore_id < RTE_MAX_LCORE; lcore_id++) {
+		if (cfg->lcore_role[lcore_id] == ROLE_OFF)
+			continue;
+		if (callback_init(callback, lcore_id) == 0)
+			continue;
+		/* Callback refused init for this lcore, uninitialize all
+		 * previous lcore.
+		 */
+		for (; lcore_id != 0; lcore_id--) {
+			if (cfg->lcore_role[lcore_id - 1] == ROLE_OFF)
+				continue;
+			callback_uninit(callback, lcore_id - 1);
+		}
+		free(callback);
+		callback = NULL;
+		goto out;
+	}
+no_init:
+	TAILQ_INSERT_TAIL(&lcore_callbacks, callback, next);
+	RTE_LOG(DEBUG, EAL, "Registered new lcore callback %s (%sinit, %suninit).\n",
+		callback->name, callback->init == NULL ? "NO " : "",
+		callback->uninit == NULL ? "NO " : "");
+out:
+	rte_spinlock_unlock(&lcore_lock);
+	return callback;
+}
+
+void
+rte_lcore_callback_unregister(void *handle)
+{
+	struct rte_config *cfg = rte_eal_get_configuration();
+	struct lcore_callback *callback = handle;
+	unsigned int lcore_id;
+
+	rte_spinlock_lock(&lcore_lock);
+	if (callback->uninit == NULL)
+		goto no_uninit;
+	for (lcore_id = 0; lcore_id < RTE_MAX_LCORE; lcore_id++) {
+		if (cfg->lcore_role[lcore_id] == ROLE_OFF)
+			continue;
+		callback_uninit(callback, lcore_id);
+	}
+no_uninit:
+	TAILQ_REMOVE(&lcore_callbacks, callback, next);
+	rte_spinlock_unlock(&lcore_lock);
+	RTE_LOG(DEBUG, EAL, "Unregistered lcore callback %s-%p.\n",
+		callback->name, callback->arg);
+	free(callback->name);
+	free(callback);
+}
 
 unsigned int
 eal_lcore_non_eal_allocate(void)
 {
 	struct rte_config *cfg = rte_eal_get_configuration();
+	struct lcore_callback *callback;
+	struct lcore_callback *prev;
 	unsigned int lcore_id;
 
 	rte_spinlock_lock(&lcore_lock);
@@ -238,8 +341,30 @@ eal_lcore_non_eal_allocate(void)
 		cfg->lcore_count++;
 		break;
 	}
-	if (lcore_id == RTE_MAX_LCORE)
+	if (lcore_id == RTE_MAX_LCORE) {
 		RTE_LOG(DEBUG, EAL, "No lcore available.\n");
+		goto out;
+	}
+	TAILQ_FOREACH(callback, &lcore_callbacks, next) {
+		if (callback_init(callback, lcore_id) == 0)
+			continue;
+		/* Callback refused init for this lcore, call uninit for all
+		 * previous callbacks.
+		 */
+		prev = TAILQ_PREV(callback, lcore_callbacks_head, next);
+		while (prev != NULL) {
+			callback_uninit(prev, lcore_id);
+			prev = TAILQ_PREV(callback, lcore_callbacks_head,
+				next);
+		}
+		RTE_LOG(DEBUG, EAL, "Initialization refused for lcore %u.\n",
+			lcore_id);
+		cfg->lcore_role[lcore_id] = ROLE_OFF;
+		cfg->lcore_count--;
+		lcore_id = RTE_MAX_LCORE;
+		goto out;
+	}
+out:
 	rte_spinlock_unlock(&lcore_lock);
 	return lcore_id;
 }
@@ -248,11 +373,15 @@ void
 eal_lcore_non_eal_release(unsigned int lcore_id)
 {
 	struct rte_config *cfg = rte_eal_get_configuration();
+	struct lcore_callback *callback;
 
 	rte_spinlock_lock(&lcore_lock);
-	if (cfg->lcore_role[lcore_id] == ROLE_NON_EAL) {
-		cfg->lcore_role[lcore_id] = ROLE_OFF;
-		cfg->lcore_count--;
-	}
+	if (cfg->lcore_role[lcore_id] != ROLE_NON_EAL)
+		goto out;
+	TAILQ_FOREACH(callback, &lcore_callbacks, next)
+		callback_uninit(callback, lcore_id);
+	cfg->lcore_role[lcore_id] = ROLE_OFF;
+	cfg->lcore_count--;
+out:
 	rte_spinlock_unlock(&lcore_lock);
 }
diff --git a/lib/librte_eal/common/eal_private.h b/lib/librte_eal/common/eal_private.h
index 73238ff157..fc79564111 100644
--- a/lib/librte_eal/common/eal_private.h
+++ b/lib/librte_eal/common/eal_private.h
@@ -401,7 +401,8 @@ uint64_t get_tsc_freq_arch(void);
  *
  * @return
  *   - the id of a lcore with role ROLE_NON_EAL on success.
- *   - RTE_MAX_LCORE if none was available.
+ *   - RTE_MAX_LCORE if none was available or initializing was refused (see
+ *     rte_lcore_callback_register).
  */
 unsigned int eal_lcore_non_eal_allocate(void);
 
diff --git a/lib/librte_eal/include/rte_lcore.h b/lib/librte_eal/include/rte_lcore.h
index ea86220394..27b29a1f87 100644
--- a/lib/librte_eal/include/rte_lcore.h
+++ b/lib/librte_eal/include/rte_lcore.h
@@ -229,6 +229,74 @@ unsigned int rte_get_next_lcore(unsigned int i, int skip_master, int wrap);
 	     i<RTE_MAX_LCORE;						\
 	     i = rte_get_next_lcore(i, 1, 0))
 
+/**
+ * Callback prototype for initializing lcores.
+ *
+ * @param lcore_id
+ *   The lcore to consider.
+ * @param arg
+ *   An opaque pointer passed at callback registration.
+ * @return
+ *   - -1 when refusing this operation,
+ *   - 0 otherwise.
+ */
+typedef int (*rte_lcore_init_cb)(unsigned int lcore_id, void *arg);
+
+/**
+ * Callback prototype for uninitializing lcores.
+ *
+ * @param lcore_id
+ *   The lcore to consider.
+ * @param arg
+ *   An opaque pointer passed at callback registration.
+ */
+typedef void (*rte_lcore_uninit_cb)(unsigned int lcore_id, void *arg);
+
+/**
+ * Register callbacks invoked when initializing and uninitializing a lcore.
+ *
+ * This function calls the init callback with all initialized lcores.
+ * Any error reported by the init callback triggers a rollback calling the
+ * uninit callback for each lcore.
+ * If this step succeeds, the callbacks are put in the lcore callbacks list
+ * that will get called for each lcore allocation/release.
+ *
+ * Note: callbacks execution is serialised under a lock protecting the lcores
+ * and callbacks list.
+ *
+ * @param name
+ *   A name serving as a small description for this callback.
+ * @param init
+ *   The callback invoked when a lcore_id is initialized.
+ * @param uninit
+ *   The callback invoked when a lcore_id is uninitialized.
+ * @param arg
+ *   An optional argument that gets passed to the callback when it gets
+ *   invoked.
+ * @return
+ *   On success, returns an opaque pointer for the registered object.
+ *   On failure (either memory allocation issue in the function itself or an
+ *   error is returned by the init callback itself), returns NULL.
+ */
+__rte_experimental
+void *
+rte_lcore_callback_register(const char *name, rte_lcore_init_cb init,
+	rte_lcore_uninit_cb uninit, void *arg);
+
+/**
+ * Unregister callbacks previously registered with rte_lcore_callback_register.
+ *
+ * This function calls the uninit callback with all initialized lcores.
+ * The callbacks are then removed from the lcore callbacks list.
+ *
+ * @param handle
+ *   The handle pointer returned by a former successful call to
+ *   rte_lcore_callback_register.
+ */
+__rte_experimental
+void
+rte_lcore_callback_unregister(void *handle);
+
 /**
  * Set core affinity of the current thread.
  * Support both EAL and non-EAL thread and update TLS.
diff --git a/lib/librte_eal/rte_eal_version.map b/lib/librte_eal/rte_eal_version.map
index 5503dd7620..c3e762c1d9 100644
--- a/lib/librte_eal/rte_eal_version.map
+++ b/lib/librte_eal/rte_eal_version.map
@@ -395,6 +395,8 @@ EXPERIMENTAL {
 	rte_trace_save;
 
 	# added in 20.08
+	rte_lcore_callback_register;
+	rte_lcore_callback_unregister;
 	rte_thread_register;
 	rte_thread_unregister;
 };
-- 
2.23.0