iio.h: Update iio_context_get_xml()

Instead of returning a string allocated alongside the IIO context, it
will now return a string allocated on the heap, that has to be freed
with free() afterwards. The function can now also return errors.

The advantage of this change is multiple:
- IIO contexts now don't have a huge XML string allocated during their
  whole lifetime;
- If the application does not call iio_context_get_xml(), then all the
  internal functions used to generate the XML string in the first place
  are dead code, and when building statically, can be garbage-collected.

Signed-off-by: Paul Cercueil <[email protected]>

context.c

@@ -181,7 +181,7 @@ static ssize_t iio_snprintf_context_xml(char *ptr, ssize_t len,
 }
 
 /* Returns a string containing the XML representation of this context */
-static char * iio_context_create_xml(const struct iio_context *ctx)
+char * iio_context_get_xml(const struct iio_context *ctx)
 {
 	ssize_t len;
 	char *str;
@@ -251,11 +251,6 @@ void iio_context_set_pdata(struct iio_context *ctx, struct iio_context_pdata *d)
 	ctx->pdata = d;
 }
 
-const char * iio_context_get_xml(const struct iio_context *ctx)
-{
-	return ctx->xml;
-}
-
 const char * iio_context_get_name(const struct iio_context *ctx)
 {
 	return ctx->name;
@@ -284,7 +279,6 @@ void iio_context_destroy(struct iio_context *ctx)
 	for (i = 0; i < ctx->nb_devices; i++)
 		free_device(ctx->devices[i]);
 	free(ctx->devices);
-	free(ctx->xml);
 	free(ctx->description);
 	free(ctx->git_tag);
 	free(ctx->pdata);
@@ -340,12 +334,7 @@ int iio_context_init(struct iio_context *ctx)
 	for (i = 0; i < ctx->nb_devices; i++)
 		reorder_channels(ctx->devices[i]);
 
-	if (ctx->xml)
-		return 0;
-
-	ctx->xml = iio_context_create_xml(ctx);
-
-	return iio_err(ctx->xml);
+	return 0;
 }
 
 unsigned int iio_context_get_version_major(const struct iio_context *ctx)

iio-private.h

@@ -92,8 +92,6 @@ struct iio_context {
 	struct iio_device **devices;
 	unsigned int nb_devices;
 
-	char *xml;
-
 	char **values;
 	struct iio_attr_list attrlist;
 

include/iio/iio.h

@@ -601,8 +601,9 @@ __api __pure const char * iio_context_get_version_tag(const struct iio_context *
 
 /** @brief Obtain a XML representation of the given context
  * @param ctx A pointer to an iio_context structure
- * @return A pointer to a static NULL-terminated string */
-__api __check_ret __pure const char * iio_context_get_xml(const struct iio_context *ctx);
+ * @return On success, an allocated string. Must be deallocated with free().
+ * @return On failure, a pointer-encoded error is returned */
+__api __check_ret char * iio_context_get_xml(const struct iio_context *ctx);
 
 
 /** @brief Get the name of the given context