Merged in timuralp/liberasurecode/check_available_backend (pull request #22)

Add a method to check if a backend is present.

4 files changed, 60 insertions, 20 deletions

diff --git a/include/erasurecode/erasurecode.h b/include/erasurecode/erasurecode.h
index 793b829..f8621a4 100644
--- a/include/erasurecode/erasurecode.h
+++ b/include/erasurecode/erasurecode.h
@@ -93,6 +93,15 @@ struct ec_args {
 /* liberasurecode frontend API functions */
 
 /**
+ * Checks if a given backend is available.
+ *
+ * @param backend_id - one of the supported backends.
+ *
+ * @returns 1 if a backend is available; 0 otherwise
+ */
+int liberasurecode_backend_available(const ec_backend_id_t backend_id);
+
+/**
  * Create a liberasurecode instance and return a descriptor 
  * for use with EC operations (encode, decode, reconstruct)
  *
diff --git a/include/erasurecode/erasurecode_backend.h b/include/erasurecode/erasurecode_backend.h
index d62c6fb..4199344 100644
--- a/include/erasurecode/erasurecode_backend.h
+++ b/include/erasurecode/erasurecode_backend.h
@@ -142,7 +142,7 @@ int liberasurecode_backend_instance_unregister(ec_backend_t instance);
 
 
 /* Generic dlopen/dlclose routines */
-int liberasurecode_backend_open(ec_backend_t instance);
+void* liberasurecode_backend_open(ec_backend_t instance);
 int liberasurecode_backend_close(ec_backend_t instance);
 
 
diff --git a/src/erasurecode.c b/src/erasurecode.c
index 13e5f02..6528eec 100644
--- a/src/erasurecode.c
+++ b/src/erasurecode.c
@@ -168,21 +168,10 @@ static void print_dlerror(const char *caller)
 }
 
 /* Generic dlopen/dlclose routines */
-int liberasurecode_backend_open(ec_backend_t instance)
+void* liberasurecode_backend_open(ec_backend_t instance)
 {
-    if (instance && NULL != instance->desc.backend_sohandle)
-        return 0;
-
     /* Use RTLD_LOCAL to avoid symbol collisions */
-    instance->desc.backend_sohandle = dlopen(instance->common.soname,
-                                             RTLD_LAZY | RTLD_LOCAL);
-    if (NULL == instance->desc.backend_sohandle) {
-        print_dlerror(__func__);
-        return -EBACKENDNOTAVAIL;
-    }
-
-    dlerror();    /* Clear any existing errors */
-    return 0;
+    return dlopen(instance->common.soname, RTLD_LAZY | RTLD_LOCAL);
 }
 
 int liberasurecode_backend_close(ec_backend_t instance)
@@ -226,6 +215,28 @@ liberasurecode_exit(void) {
 /* =~=*=~==~=*=~= liberasurecode frontend API implementation =~=*=~==~=*=~== */
 
 /**
+ * Checks if a given backend is available.
+ *
+ * @param backend_id - one of the supported backends.
+ *
+ * @returns 1 if a backend is available; 0 otherwise
+ */
+int liberasurecode_backend_available(const ec_backend_id_t backend_id) {
+    struct ec_backend backend;
+    if (backend_id >= EC_BACKENDS_MAX)
+        return 0;
+
+    backend.desc.backend_sohandle = liberasurecode_backend_open(
+            ec_backends_supported[backend_id]);
+    if (!backend.desc.backend_sohandle) {
+        return 0;
+    }
+
+    liberasurecode_backend_close(&backend);
+    return 1;
+}
+
+/**
  * Create a liberasurecode instance and return a descriptor
  * for use with EC operations (encode, decode, reconstruct)
  *
@@ -247,7 +258,6 @@ liberasurecode_exit(void) {
 int liberasurecode_instance_create(const ec_backend_id_t id,
                                    struct ec_args *args)
 {
-    int err = 0;
     ec_backend_t instance = NULL;
     struct ec_backend_args bargs;
     if (!args)
@@ -274,11 +284,14 @@ int liberasurecode_instance_create(const ec_backend_id_t id,
 
     /* Open backend .so if not already open */
     /* .so handle is returned in instance->desc.backend_sohandle */
-    err = liberasurecode_backend_open(instance);
-    if (err < 0) {
-        /* ignore during init, return the same handle */
-        free(instance);
-        return err;
+    if (!instance->desc.backend_sohandle) {
+        instance->desc.backend_sohandle = liberasurecode_backend_open(instance);
+        if (!instance->desc.backend_sohandle) {
+            /* ignore during init, return the same handle */
+            print_dlerror(__func__);
+            free(instance);
+            return -EBACKENDNOTAVAIL;
+        }
     }
 
     /* Call private init() for the backend */
diff --git a/test/liberasurecode_test.c b/test/liberasurecode_test.c
index e8b3179..8ee84c4 100644
--- a/test/liberasurecode_test.c
+++ b/test/liberasurecode_test.c
@@ -471,6 +471,16 @@ static void test_create_and_destroy_backend(
     assert(0 == liberasurecode_instance_destroy(desc));
 }
 
+static void test_backend_available(ec_backend_id_t be_id) {
+    assert(1 == liberasurecode_backend_available(be_id));
+}
+
+static void test_backend_available_invalid_args(ec_backend_id_t be_id)
+{
+    int ret = liberasurecode_backend_available(EC_BACKENDS_MAX);
+    assert(ret < 0);
+}
+
 static void test_create_backend_invalid_args()
 {
     int desc = liberasurecode_instance_create(-1, &null_args);
@@ -1522,6 +1532,14 @@ static void test_verify_stripe_metadata_frag_idx_invalid(
 //static void test_verify_str
 
 struct testcase testcases[] = {
+    {"test_backend_available_invalid_args",
+        test_backend_available_invalid_args,
+        EC_BACKENDS_MAX, 0,
+        .skip = false},
+    {"test_backend_available",
+        test_backend_available,
+        EC_BACKEND_NULL, 0,
+        .skip =  false},
     {"test_create_backend_invalid_args",
         test_create_backend_invalid_args,
         EC_BACKENDS_MAX, CHKSUM_TYPES_MAX,