+/*
+ * Copyright (C) 2020 Jérémie Galarneau <jeremie.galarneau@efficios.com>
+ *
+ * SPDX-License-Identifier: LGPL-2.1-only
+ *
+ */
+
+#ifndef LTTNG_PAYLOAD_VIEW_H
+#define LTTNG_PAYLOAD_VIEW_H
+
+#include <common/buffer-view.h>
+#include <common/dynamic-array.h>
+
+struct lttng_payload;
+
+/*
+ * An lttng_payload_view references a payload and allows code to share
+ * a `const` version of a subset of a payload.
+ *
+ * A payload view is invalidated whenever its source (a payload, or another
+ * payload view) is modified.
+ *
+ * While a payload view does not allow users to modify the underlying bytes
+ * of the payload, it can be used to 'pop' file descriptors using an iterator
+ * belonging to the top-level payload view.
+ *
+ * Hence, a payload view created from a payload or a dynamic buffer contains
+ * an implicit file descriptor iterator. Any payload view created from another
+ * payload view will share the same underlying file descriptor iterator.
+ *
+ * The rationale for this is that a payload is never consumed directly, it
+ * must be consumed through a payload view.
+ *
+ * Typically, a payload view will be used to rebuild a previously serialized
+ * object hierarchy. Sharing an underlying iterator allows aggregate objects
+ * to provide a restricted view of the payload to their members, which will
+ * report the number of bytes consumed and `pop` the file descriptors they
+ * should own. In return, those objects can create an even narrower view for
+ * their children, allowing them to also consume file descriptors.
+ *
+ * Note that a payload view never assumes any ownership of the underlying
+ * payload.
+ */
+struct lttng_payload_view {
+ struct lttng_buffer_view buffer;
+ /* private */
+ const struct lttng_dynamic_array _fds;
+ struct {
+ size_t *p_fds_position;
+ size_t fds_position;
+ } _iterator;
+};
+
+/**
+ * Return a payload view referencing a subset of a payload.
+ *
+ * @payload Source payload to reference
+ * @offset Offset to apply to the payload's buffer
+ * @len Length of the contents to reference. Passing -1 will
+ * cause the view to reference the whole payload from the
+ * offset provided.
+ */
+LTTNG_HIDDEN
+struct lttng_payload_view lttng_payload_view_from_payload(
+ const struct lttng_payload *payload, size_t offset,
+ ptrdiff_t len);
+
+/**
+ * Return a payload view referencing a subset of a payload referenced by
+ * another payload view.
+ *
+ * @view Source payload view to reference
+ * @offset Offset to apply to the payload view's buffer view
+ * @len Length of the contents to reference. Passing -1 will
+ * cause the payload view to reference the whole payload view's
+ * buffer view from the offset provided.
+ */
+LTTNG_HIDDEN
+struct lttng_payload_view lttng_payload_view_from_view(
+ struct lttng_payload_view *view, size_t offset,
+ ptrdiff_t len);
+
+/**
+ * Return a payload view referencing a subset of a dynamic buffer.
+ *
+ * Meant as an adapter for code paths that need to create a payload view
+ * from an existing dynamic buffer.
+ *
+ * @src Source dynamic buffer to reference
+ * @offset Offset to apply to the payload's buffer
+ * @len Length of the buffer contents to reference. Passing -1 will
+ * cause the payload view to reference the whole payload from the
+ * offset provided.
+ */
+LTTNG_HIDDEN
+struct lttng_payload_view lttng_payload_view_from_dynamic_buffer(
+ const struct lttng_dynamic_buffer *buffer, size_t offset,
+ ptrdiff_t len);
+
+/**
+ * Pop an fd from a payload view.
+ * No ownership of the file descriptor is assumed by the payload.
+ *
+ * @payload Payload instance
+ *
+ * Returns a file descriptor on success, -1 on error.
+ */
+LTTNG_HIDDEN
+int lttng_payload_view_pop_fd(struct lttng_payload_view *payload_view);
+
+#endif /* LTTNG_PAYLOAD_VIEW_H */
projects / lttng-tools.git / commitdiff
