Detect missing symbols used with kallsyms_lookup at compile time

[lttng-modules.git] / wrapper / splice.c

/* SPDX-License-Identifier: (GPL-2.0 or LGPL-2.1)
 *
 * wrapper/splice.c
 *
 * wrapper around splice_to_pipe. Using KALLSYMS to get its address when
 * available, else we need to have a kernel that exports this function to GPL
 * modules. The export was introduced in kernel 4.2.
 *
 * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 */

#include <lttng-kernel-version.h>

#if (defined(CONFIG_KALLSYMS) \
	&& (LINUX_VERSION_CODE < KERNEL_VERSION(4,2,0)))

#include <linux/kallsyms.h>
#include <linux/fs.h>
#include <linux/splice.h>
#include <wrapper/kallsyms.h>

static
ssize_t (*splice_to_pipe_sym)(struct pipe_inode_info *pipe,
			      struct splice_pipe_desc *spd);

ssize_t wrapper_splice_to_pipe(struct pipe_inode_info *pipe,
			       struct splice_pipe_desc *spd)
{
	if (!splice_to_pipe_sym)
		splice_to_pipe_sym = (void *) kallsyms_lookup_funcptr("splice_to_pipe"); 
	if (splice_to_pipe_sym) {
		return splice_to_pipe_sym(pipe, spd);
	} else {
		printk_once(KERN_WARNING "LTTng: splice_to_pipe symbol lookup failed.\n");
		return -ENOSYS;
	}
}

/*
 * Canary function to check for 'splice_to_pipe()' at compile time.
 *
 * From 'include/linux/splice.h':
 *
 *   extern ssize_t splice_to_pipe(struct pipe_inode_info *,
 *                                 struct splice_pipe_desc *spd);
 */
__attribute__((unused)) static
ssize_t __canary__splice_to_pipe(struct pipe_inode_info *pipe,
				struct splice_pipe_desc *spd)
{
	return splice_to_pipe(pipe, spd);
}

#else

#include <linux/fs.h>
#include <linux/splice.h>

ssize_t wrapper_splice_to_pipe(struct pipe_inode_info *pipe,
			       struct splice_pipe_desc *spd)
{
	return splice_to_pipe(pipe, spd);
}

#endif