docs: Add supported versions and fix-backport policy

[lttng-tools.git] / src / bin / lttng-sessiond / ust-registry-session.hpp

/*
 * Copyright (C) 2022 Jérémie Galarneau <jeremie.galarneau@efficios.com>
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 */

#ifndef LTTNG_UST_REGISTRY_SESSION_H
#define LTTNG_UST_REGISTRY_SESSION_H

#include "clock-class.hpp"
#include "session.hpp"
#include "trace-class.hpp"
#include "ust-clock-class.hpp"
#include "ust-registry-channel.hpp"
#include "ust-registry.hpp"

#include <common/make-unique-wrapper.hpp>

#include <lttng/lttng.h>

#include <cstdint>
#include <ctime>
#include <string>
#include <unistd.h>

namespace lttng {
namespace sessiond {
namespace ust {

class registry_enum;
class registry_session;

namespace details {
void locked_registry_session_release(registry_session *session);
} /* namespace details */

class registry_session : public lttng::sessiond::trace::trace_class {
public:
	using locked_ptr =
		std::unique_ptr<registry_session,
				lttng::memory::create_deleter_class<
					registry_session,
					details::locked_registry_session_release>::deleter>;

	virtual lttng_buffer_type buffering_scheme() const noexcept = 0;
	locked_ptr lock() noexcept;

	void add_channel(uint64_t channel_key);

	/* A channel is protected by its parent registry session's lock. */
	lttng::sessiond::ust::registry_channel& channel(uint64_t channel_key) const;

	void remove_channel(uint64_t channel_key, bool notify);

	void create_or_find_enum(int session_objd,
				 const char *enum_name,
				 struct lttng_ust_ctl_enum_entry *raw_entries,
				 size_t nr_entries,
				 uint64_t *enum_id);
	registry_enum::const_rcu_protected_reference enumeration(const char *enum_name,
								 uint64_t enum_id) const;

	void regenerate_metadata();

	~registry_session() override;
	registry_session(const registry_session&) = delete;
	registry_session(registry_session&&) = delete;
	registry_session& operator=(registry_session&&) = delete;
	registry_session& operator=(const registry_session&) = delete;

	const lttng::sessiond::trace::type *packet_header() const noexcept override;

	/*
	 * With multiple writers and readers, use this lock to access
	 * the registry. Can nest within the ust app session lock.
	 * Also acts as a registry serialization lock. Used by registry
	 * readers to serialize the registry information sent from the
	 * sessiond to the consumerd.
	 *
	 * The consumer socket lock nests within this lock.
	 */
	mutable pthread_mutex_t _lock;

	/* Generated metadata, not null-terminated. */
	char *_metadata = nullptr; /*  */
	size_t _metadata_len = 0;
	/* Length of bytes sent to the consumer. */
	size_t _metadata_len_sent = 0;
	/* Current version of the metadata. */
	uint64_t _metadata_version = 0;

	/*
	 * Unique key to identify the metadata on the consumer side.
	 */
	uint64_t _metadata_key = 0;
	/*
	 * Indicates if the metadata is closed on the consumer side. This is to
	 * avoid double close of metadata when an application unregisters AND
	 * deletes its sessions.
	 */
	bool _metadata_closed = false;

protected:
	/* Prevent instanciation of this base class. */
	registry_session(const struct lttng::sessiond::trace::abi& abi,
			 unsigned int app_tracer_version_major,
			 unsigned int app_tracer_version_minor,
			 const char *root_shm_path,
			 const char *shm_path,
			 uid_t euid,
			 gid_t egid,
			 uint64_t tracing_id);
	void accept(trace::trace_class_environment_visitor& environment_visitor) const override;
	void _generate_metadata();

private:
	uint32_t _get_next_channel_id();
	void _increase_metadata_size(size_t reservation_length);
	void _append_metadata_fragment(const std::string& fragment);
	void _reset_metadata();
	void _destroy_enum(registry_enum *reg_enum) noexcept;
	registry_enum *_lookup_enum(const registry_enum *target_enum) const;
	lttng::sessiond::trace::type::cuptr _create_packet_header() const;

	void _accept_on_clock_classes(
		lttng::sessiond::trace::trace_class_visitor& trace_class_visitor) const final;
	void _accept_on_stream_classes(
		lttng::sessiond::trace::trace_class_visitor& trace_class_visitor) const final;

	/* Next channel ID available for a newly registered channel. */
	uint32_t _next_channel_id = 0;

	/* Once this value reaches UINT32_MAX, no more id can be allocated. */
	uint32_t _used_channel_id = 0;

	/* Next enumeration ID available. */
	uint64_t _next_enum_id = 0;

	size_t _metadata_alloc_len = 0;

	/*
	 * Those fields are only used when a session is created with
	 * the --shm-path option. In this case, the metadata is output
	 * twice: once to the consumer, as ususal, but a second time
	 * also in the shm path directly. This is done so that a copy
	 * of the metadata that is as fresh as possible is available
	 * on the event of a crash.
	 *
	 * root_shm_path contains the shm-path provided by the user, along with
	 * the session's name and timestamp:
	 *   e.g. /tmp/my_shm/my_session-20180612-135822
	 *
	 * shm_path contains the full path of the memory buffers:
	 *   e.g. /tmp/my_shm/my_session-20180612-135822/ust/uid/1000/64-bit
	 *
	 * metadata_path contains the full path to the metadata file that
	 * is kept for the "crash buffer" extraction:
	 *  e.g.
	 * /tmp/my_shm/my_session-20180612-135822/ust/uid/1000/64-bit/metadata
	 *
	 * Note that this is not the trace's final metadata file. It is
	 * only meant to be used to read the contents of the ring buffers
	 * in the event of a crash.
	 *
	 * metadata_fd is a file descriptor that points to the file at
	 * 'metadata_path'.
	 */
	const std::string _root_shm_path;
	const std::string _shm_path;
	const std::string _metadata_path;

	/* File-backed metadata FD */
	int _metadata_fd = -1;

	/*
	 * Hash table containing channels sent by the UST tracer. MUST
	 * be accessed with a RCU read side lock acquired.
	 */
	lttng_ht::uptr _channels;

	/* Enumerations table. */
	lttng_ht::uptr _enums;

	/* User and group owning the session. */
	const uid_t _uid;
	const gid_t _gid;

	/*
	 * Copy of the tracer version when the first app is registered.
	 * It is used if we need to regenerate the metadata.
	 */
	const struct {
		uint32_t major, minor;
	} _app_tracer_version;

	/* The id of the parent session. */
	const ltt_session::id_t _tracing_id;

	lttng::sessiond::ust::clock_class::cuptr _clock;
	const lttng::sessiond::trace::trace_class_visitor::cuptr _metadata_generating_visitor;
	lttng::sessiond::trace::type::cuptr _packet_header;
};

} /* namespace ust */
} /* namespace sessiond */
} /* namespace lttng */

#endif /* LTTNG_UST_REGISTRY_SESSION_H */