iio: create iio_context_create_from_backend() helper and use it for l…

…ocal & xml

The creation of a context can be tied to an iio_backend object that acts as
a template for some context parameters.
Using an iio_backend object for IIO context creation allows us to hide the
assignments of the name, iio_backend_ops, description, private data and
possibly other parameters in the future.

For now, this ties it to the local & xml backends. The other backends seem
to be iiod client-type backends. Using the iio_backend object there
requires a bit more rework.

At a later point in time, the iio_context_create_from_backend() helper
should also do more validation for the backend object.

Signed-off-by: Alexandru Ardelean <[email protected]>

context.c

@@ -182,6 +182,51 @@ char * iio_context_create_xml(const struct iio_context *ctx)
 	return NULL;
 }
 
+struct iio_context * iio_context_create_from_backend(
+		const struct iio_backend *backend,
+		const char *description)
+{
+	struct iio_context *ctx;
+	int ret;
+
+	if (!backend) {
+		errno = EINVAL;
+		return NULL;
+	}
+
+	ctx = zalloc(sizeof(*ctx));
+	if (!ctx) {
+		errno = ENOMEM;
+		return NULL;
+	}
+
+	ret = -ENOMEM;
+	if (backend->sizeof_context_pdata) {
+		ctx->pdata = zalloc(backend->sizeof_context_pdata);
+		if (!ctx->pdata)
+			goto err_free_ctx;
+	}
+
+	if (description) {
+		ctx->description = iio_strdup(description);
+		if (!ctx->description)
+			goto err_free_pdata;
+	}
+
+	ctx->name = backend->name;
+	ctx->ops = backend->ops;
+
+	return ctx;
+
+err_free_pdata:
+	if (ctx->pdata)
+		free(ctx->pdata);
+err_free_ctx:
+	free(ctx);
+	errno = -ret;
+	return NULL;
+}
+
 const char * iio_context_get_xml(const struct iio_context *ctx)
 {
 	return ctx->xml;

iio-backend.h

@@ -23,6 +23,10 @@
 struct iio_device;
 struct iio_context;
 
+enum iio_backend_api_ver {
+	IIO_BACKEND_API_V1 = 1,
+};
+
 enum iio_attr_type {
 	IIO_ATTR_TYPE_DEVICE = 0,
 	IIO_ATTR_TYPE_DEBUG,
@@ -72,4 +76,24 @@ struct iio_backend_ops {
 	int (*set_timeout)(struct iio_context *ctx, unsigned int timeout);
 };
 
+/**
+ * struct iio_backend - IIO backend object (API version 1)
+ * @api_version			API version for interfacing with libiio core library
+ * @name			Name of this backend
+ * @uri_prefix			URI prefix for this backend
+ * @ops				Reference to backend ops
+ * @sizeof_context_pdata	Size of private data for the IIO contexts generated by this backend
+ */
+struct iio_backend {
+	unsigned int			api_version;
+	const char			*name;
+	const char			*uri_prefix;
+	const struct iio_backend_ops	*ops;
+	unsigned int			sizeof_context_pdata;
+};
+
+__api struct iio_context * iio_context_create_from_backend(
+		const struct iio_backend *backend,
+		const char *description);
+
 #endif /* __IIO_BACKEND_H__ */

local.c

@@ -1948,6 +1948,14 @@ static const struct iio_backend_ops local_ops = {
 	.cancel = local_cancel,
 };
 
+static const struct iio_backend local_backend = {
+	.api_version = IIO_BACKEND_API_V1,
+	.name = "local",
+	.uri_prefix = "local:",
+	.ops = &local_ops,
+	.sizeof_context_pdata = sizeof(struct iio_context_pdata),
+};
+
 static void init_data_scale(struct iio_channel *chn)
 {
 	char *end, buf[1024];
@@ -2038,37 +2046,29 @@ static int populate_context_attrs(struct iio_context *ctx, const char *file)
 
 struct iio_context * local_create_context(void)
 {
+	struct iio_context *ctx;
+	char *description;
 	int ret = -ENOMEM;
 	unsigned int len;
 	struct utsname uts;
-	struct iio_context *ctx = zalloc(sizeof(*ctx));
-	if (!ctx)
-		goto err_set_errno;
-
-	ctx->ops = &local_ops;
-	ctx->name = "local";
-
-	ctx->pdata = zalloc(sizeof(*ctx->pdata));
-	if (!ctx->pdata) {
-		free(ctx);
-		goto err_set_errno;
-	}
-
-	local_set_timeout(ctx, DEFAULT_TIMEOUT_MS);
 
 	uname(&uts);
 	len = strlen(uts.sysname) + strlen(uts.nodename) + strlen(uts.release)
 		+ strlen(uts.version) + strlen(uts.machine);
-	ctx->description = malloc(len + 5); /* 4 spaces + EOF */
-	if (!ctx->description) {
-		free(ctx->pdata);
-		free(ctx);
+	description = malloc(len + 5); /* 4 spaces + EOF */
+	if (!description)
 		goto err_set_errno;
-	}
 
-	iio_snprintf(ctx->description, len + 5, "%s %s %s %s %s", uts.sysname,
+	iio_snprintf(description, len + 5, "%s %s %s %s %s", uts.sysname,
 			uts.nodename, uts.release, uts.version, uts.machine);
 
+	ctx = iio_context_create_from_backend(&local_backend, description);
+	free(description);
+	if (!ctx)
+		goto err_set_errno;
+
+	local_set_timeout(ctx, DEFAULT_TIMEOUT_MS);
+
 	ret = foreach_in_dir(ctx, "/sys/bus/iio/devices", true, create_device);
 	if (ret < 0)
 		goto err_context_destroy;

xml.c

@@ -352,6 +352,13 @@ static const struct iio_backend_ops xml_ops = {
 	.clone = xml_clone,
 };
 
+static const struct iio_backend xml_backend = {
+	.api_version = IIO_BACKEND_API_V1,
+	.name = "xml",
+	.uri_prefix = "xml:",
+	.ops = &xml_ops,
+};
+
 static int parse_context_attr(struct iio_context *ctx, xmlNode *n)
 {
 	xmlAttr *attr;
@@ -376,29 +383,28 @@ static struct iio_context * iio_create_xml_context_helper(xmlDoc *doc)
 	xmlNode *root, *n;
 	xmlAttr *attr;
 	int err = -ENOMEM;
-	struct iio_context *ctx = zalloc(sizeof(*ctx));
-	if (!ctx)
-		goto err_set_errno;
-
-	ctx->name = "xml";
-	ctx->ops = &xml_ops;
+	struct iio_context *ctx;
+	const char *description = NULL;
 
 	root = xmlDocGetRootElement(doc);
 	if (strcmp((char *) root->name, "context")) {
 		IIO_ERROR("Unrecognized XML file\n");
 		err = -EINVAL;
-		goto err_context_destroy;
+		goto err_set_errno;
 	}
 
 	for (attr = root->properties; attr; attr = attr->next) {
 		if (!strcmp((char *) attr->name, "description"))
-			ctx->description = iio_strdup(
-					(char *) attr->children->content);
+			description = (const char *)attr->children->content;
 		else if (strcmp((char *) attr->name, "name"))
 			IIO_WARNING("Unknown parameter \'%s\' in <context>\n",
 					(char *) attr->children->content);
 	}
 
+	ctx = iio_context_create_from_backend(&xml_backend, description);
+	if (!ctx)
+		goto err_set_errno;
+
 	for (n = root->children; n; n = n->next) {
 		struct iio_device *dev;