wernermisc/fakefile/slave.c

/*
 * slave.c - Fakefile slave library
 *
 * Copyright 2012 by Werner Almesberger
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 */

#include <stdarg.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <assert.h>
#include <sys/types.h>
#include <sys/stat.h>

#define	__USE_GNU	/* for RTLD_NEXT */
#include <dlfcn.h>

#include "util.h"
#include "fakefile.h"
#include "comm.h"


#define	DUMMY_FILE	"/dev/null"
#define	master	NULL


static struct fd_entry {
	int fd;
	struct fd_entry *next;
} *fake_fds = NULL;

static int (*libc_close)(int fd);
static int (*libc_dup)(int oldfd);
static int (*libc_dup2)(int oldfd, int newfd);
static int (*libc_open)(const char *pathname, int flags, mode_t mode);
static ssize_t (*libc_read)(int fd, void *buf, size_t count);

static FILE *(*libc_fopen)(const char *path, const char *mode);

static void init_self(void)
{
	static int initialized = 0;

	if (initialized)
		return;
	libc_close = dlsym(RTLD_NEXT, "close");
	libc_dup = dlsym(RTLD_NEXT, "dup");
	libc_dup2 = dlsym(RTLD_NEXT, "dup2");
	libc_open = dlsym(RTLD_NEXT, "open");
	libc_read = dlsym(RTLD_NEXT, "read");
libc_fopen = dlsym(RTLD_NEXT, "fopen");
	if (!libc_close || !libc_dup || !libc_dup2 || !libc_open ||
	    !libc_read) {
		perror("dlsym");
		_exit(1);
	}
	initialized = 1;
}


static int get_fd(void)
{
	int fd;

	fd = libc_open(DUMMY_FILE, O_RDONLY, 0);
	if (fd < 0) {
		perror(DUMMY_FILE);
		exit(1);
	}
	assert(fd);
	return fd;
}


static void add_fake_fd(int fd)
{
	struct fd_entry *e;

	e = alloc_type(struct fd_entry);
	e->fd = fd;
	e->next = fake_fds;
	fake_fds =e;
}


static int is_fake_fd(int fd)
{
	const struct fd_entry *e;

	for (e = fake_fds; e && e->fd != fd; e = e->next);
	return !!e;
}


static int del_fake_fd(int fd)
{
	struct fd_entry **e, *next;

	for (e = &fake_fds; *e; e = &(*e)->next)
		if ((*e)->fd == fd)
			break;
	if (!*e)
		return 0;
	next = (*e)->next;
	free(*e);
	*e = next;
	(void) libc_close(fd);
	return 1;
}


int open(const char *pathname, int flags, ...)
{
	va_list ap;
	struct fakefile_msg *msg;
	size_t len;
	int mode = 0;
	int fd, res;

	init_self();
	if (flags & O_CREAT) {
		va_start(ap, flags);
		mode = va_arg(ap, int);
		va_end(ap);
	}

	fd = get_fd();
	len = strlen(pathname);

	msg = fakefile_msg_new(master, len+5*sizeof(int));
	fakefile_msg_add_int(msg, ff_et_open);
	fakefile_msg_add_int(msg, flags);
	fakefile_msg_add_int(msg, mode);
	fakefile_msg_add_int(msg, fd);
	fakefile_msg_add_int(msg, len);
	fakefile_msg_add(msg, pathname, len);
	fakefile_msg_end(msg);

	msg = fakefile_msg_recv(master);
	res = fakefile_msg_get_int(msg);
	fakefile_msg_end(msg);

//fprintf(stderr, "res %d\n", (int) res);
	if (res <= 0) {
		(void) close(fd);
		if (res < 0) {
			errno = -res;
			return -1;
		}
	}
	if (res)
		add_fake_fd(fd);
	else
		res = libc_open(pathname, flags, mode);
	return res;
}


ssize_t read(int fd, void *buf, size_t count)
{
	struct fakefile_msg *msg;
	ssize_t res;

	init_self();
	if (!is_fake_fd(fd))
		return libc_read(fd, buf, count);
	msg = fakefile_msg_new(master, 2*sizeof(int)+sizeof(size_t));
	fakefile_msg_add_int(msg, ff_et_read);
	fakefile_msg_add_int(msg, fd);
	fakefile_msg_add_size_t(msg, count);
	fakefile_msg_end(msg);

	msg = fakefile_msg_recv(master);
	res = fakefile_msg_get_size_t(msg);
	if (res > 0) {
		assert((size_t) res <= count);
		fakefile_msg_get(msg, buf, res);
	} else if (res < 0) {
		errno = -res;
		res = -1;
	}
	fakefile_msg_end(msg);
//fprintf(stderr, "READ %d\n", (int) res);
	return res;
}


int fstat(int fd, struct stat *buf)
{
	struct fakefile_msg *msg;
	int res;

	init_self();
	msg = fakefile_msg_new(master, 2*sizeof(int));
	fakefile_msg_add_int(msg, ff_et_fstat);
	fakefile_msg_add_int(msg, fd);
	fakefile_msg_end(msg);

	msg = fakefile_msg_recv(master);
	res = fakefile_msg_get_size_t(msg);
	if (res < 0) {
		errno = -res;
		res = -1;
	} else {
		fakefile_msg_get(msg, buf, sizeof(struct stat));
	}
	fakefile_msg_end(msg);

	return res;
}


int stat(const char *path, struct stat *buf)
{
	int fd, res;

	fd = open(path, O_RDONLY);
	if (fd < 0)
		return fd;
	res = fstat(fd, buf);
	(void) close(fd);

	return res;
}


int lstat(const char *path, struct stat *buf)
{
	return stat(path, buf);
}


int close(int fd)
{
	struct fakefile_msg *msg;
	int res;

	init_self();
	if (!del_fake_fd(fd))
		return libc_close(fd);

	msg = fakefile_msg_new(master, 2*sizeof(int));
	fakefile_msg_add_int(msg, ff_et_close);
	fakefile_msg_add_int(msg, fd);
	fakefile_msg_end(msg);
	
	msg = fakefile_msg_recv(master);
	res = fakefile_msg_get_int(msg);
	fakefile_msg_end(msg);

	if (res < 0) {
		errno = -res;
		return -1;
	}

	return res;
}


FILE *fopen(const char *path, const char *mode)
{
	init_self();
	fprintf(stderr, "fopen \"%s\"\n", path);
	return libc_fopen(path, mode);
}


int dup(int oldfd)
{
	init_self();
	if (is_fake_fd(oldfd)) {
		fprintf(stderr, "not supporting \"dup\" yet\n");
		exit(1);
	}
	return libc_dup(oldfd);
}



int dup2(int oldfd, int newfd)
{
	int res;

	init_self();
	if (oldfd == newfd)
		return 0;
	if (is_fake_fd(oldfd)) {
		fprintf(stderr, "not supporting \"dup2\" yet\n");
		exit(1);
	}
	if (is_fake_fd(newfd)) {
		res = close(newfd);
		if (res < 0)
			return res;
	}
	return libc_dup2(oldfd, newfd);
}