API refactoring: introduce probe context

[lttng-ust.git] / src / lib / lttng-ust / lttng-context-mnt-ns.c

/*
 * SPDX-License-Identifier: LGPL-2.1-only
 *
 * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com>
 *
 * LTTng UST mnt namespace context.
 */

#define _LGPL_SOURCE
#include <limits.h>
#include <stddef.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <lttng/ust-events.h>
#include <lttng/ust-tracer.h>
#include <lttng/ust-ringbuffer-context.h>

#include "context-internal.h"
#include "common/ns.h"

/*
 * We cache the result to ensure we don't stat(2) the proc filesystem on
 * each event. The mount namespace is global to the process.
 */
static ino_t cached_mnt_ns = NS_INO_UNINITIALIZED;

static
ino_t get_mnt_ns(void)
{
	struct stat sb;
	ino_t mnt_ns;

	mnt_ns = CMM_LOAD_SHARED(cached_mnt_ns);

	/*
	 * If the cache is populated, do nothing and return the
	 * cached inode number.
	 */
	if (caa_likely(mnt_ns != NS_INO_UNINITIALIZED))
		return mnt_ns;

	/*
	 * At this point we have to populate the cache, set the initial
	 * value to NS_INO_UNAVAILABLE (0), if we fail to get the inode
	 * number from the proc filesystem, this is the value we will
	 * cache.
	 */
	mnt_ns = NS_INO_UNAVAILABLE;

	if (stat("/proc/self/ns/mnt", &sb) == 0) {
		mnt_ns = sb.st_ino;
	}

	/*
	 * And finally, store the inode number in the cache.
	 */
	CMM_STORE_SHARED(cached_mnt_ns, mnt_ns);

	return mnt_ns;
}

/*
 * The mnt namespace can change for 3 reasons
 *  * clone(2) called with CLONE_NEWNS
 *  * setns(2) called with the fd of a different mnt ns
 *  * unshare(2) called with CLONE_NEWNS
 */
void lttng_context_mnt_ns_reset(void)
{
	CMM_STORE_SHARED(cached_mnt_ns, NS_INO_UNINITIALIZED);
}

static
size_t mnt_ns_get_size(void *priv __attribute__((unused)),
		struct lttng_ust_probe_ctx *probe_ctx __attribute__((unused)),
		size_t offset)
{
	size_t size = 0;

	size += lttng_ust_ring_buffer_align(offset, lttng_ust_rb_alignof(ino_t));
	size += sizeof(ino_t);
	return size;
}

static
void mnt_ns_record(void *priv __attribute__((unused)),
		struct lttng_ust_probe_ctx *probe_ctx __attribute__((unused)),
		struct lttng_ust_ring_buffer_ctx *ctx,
		struct lttng_ust_channel_buffer *chan)
{
	ino_t mnt_ns;

	mnt_ns = get_mnt_ns();
	chan->ops->event_write(ctx, &mnt_ns, sizeof(mnt_ns), lttng_ust_rb_alignof(mnt_ns));
}

static
void mnt_ns_get_value(void *priv __attribute__((unused)),
		struct lttng_ust_probe_ctx *probe_ctx __attribute__((unused)),
		struct lttng_ust_ctx_value *value)
{
	value->u.u64 = get_mnt_ns();
}

static const struct lttng_ust_ctx_field *ctx_field = lttng_ust_static_ctx_field(
	lttng_ust_static_event_field("mnt_ns",
		lttng_ust_static_type_integer(sizeof(ino_t) * CHAR_BIT,
				lttng_ust_rb_alignof(ino_t) * CHAR_BIT,
				lttng_ust_is_signed_type(ino_t),
				LTTNG_UST_BYTE_ORDER, 10),
		false, false),
	mnt_ns_get_size,
	mnt_ns_record,
	mnt_ns_get_value,
	NULL, NULL);

int lttng_add_mnt_ns_to_ctx(struct lttng_ust_ctx **ctx)
{
	int ret;

	if (lttng_find_context(*ctx, ctx_field->event_field->name)) {
		ret = -EEXIST;
		goto error_find_context;
	}
	ret = lttng_ust_context_append(ctx, ctx_field);
	if (ret)
		return ret;
	return 0;

error_find_context:
	return ret;
}