/*
 * PoC for using new mount API for mount.cifs
 */

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>

/*
 * For MS_*, MNT_* constants
 */
#include <sys/mount.h>

/*
 * For FSCONFIG_*, FSMOUNT_*, MOVE_* constants
 *
 * TODO: need to add configure check for header availability
 */
#include <linux/mount.h>

/*
 * For AT_* constants
 */
#include <fcntl.h>

/*
 * The new mount API syscalls have currently no wrappers in
 * glibc. Call them via syscall().
 *
 * Wrap in #ifdef to be future-proof once they eventually get wrappers
 *
 * TODO: add configure checks for fsopen symbol -> HAVE_FSOPEN
 */
#ifndef HAVE_FSOPEN
#include <sys/syscall.h>
#ifndef SYS_fsopen
enum {SYS_move_mount=429, SYS_fsopen, SYS_fsconfig, SYS_fsmount};
#endif
int fsopen(const char *fsname, unsigned int flags)
{
	return syscall(SYS_fsopen, fsname, flags);
}
int fsmount(int fd, unsigned int flags, unsigned int mount_attrs)
{
	return syscall(SYS_fsmount, fd, flags, mount_attrs);
}
int fsconfig(int fd, unsigned int cmd, const char *key, const void *value, int aux)
{
	return syscall(SYS_fsconfig, fd, cmd, key, value, aux);
}
int move_mount(int from_dirfd, const char *from_pathname, int to_dirfd, const char *to_pathname, unsigned int flags)
{
	return syscall(SYS_move_mount, from_dirfd, from_pathname, to_dirfd, to_pathname, flags);
}
#endif

/*
 * To get the kernel log emitted after a call, simply read the context fd
 *
 *     "e <message>"
 *            An error message string was logged.
 *
 *     "i <message>"
 *            An informational message string was logged.
 *
 *     "w <message>"
 *            An warning message string was logged.
 *
 *     Messages are removed from the queue as they're read.
 *
 */
void print_context_log(int fd)
{
	char buf[512];
	ssize_t rc;
	int first = 1;

	while (1) {
		memset(buf, 0, sizeof(buf));
		rc = read(fd, buf, sizeof(buf)-2);
		if (rc == 0 || (rc < 0 && errno == ENODATA)) {
			errno = 0;
			break;
		}
		else if (rc < 0) {
			perror("read");
			break;
		}
		if (first) {
			printf("kernel mount errors:\n");
			first = 0;
		}
		printf("%s", buf);
	}
}

#define ASSERT(x)					\
	do {						\
		if (!(x)) {				\
			printf("ASSERT FAIL %s\n", #x); \
			exit(1);			\
		}					\
	} while (0)

#define CHECK(x)				\
	do {					\
		if ((x) < 0) {			\
			perror(#x);		\
			exit(1);		\
		}				\
	} while (0)

#define CHECK_AND_LOG(fd, x)			\
	do {					\
		if ((x) < 0) {			\
			perror(#x);		\
			print_context_log(fd);	\
			exit(1);		\
		}				\
	} while (0)

char *g_mount_params;

/* read whole file in g_mount_params buffer */
void read_mount_params(void)
{
	int fd;
	size_t off;
	ssize_t rc;
	size_t size;

	off = 0;
	size = 2048;
	g_mount_params = malloc(size);
	if (!g_mount_params)
		goto out;

	g_mount_params[off++] = '\n';

	fd = open("/proc/fs/cifs/mount_params", O_RDONLY);
	if (fd < 0)
		goto out;

	do {
		if (size - off <= 1) {
			void *p = realloc(g_mount_params, size*2);
			if (!p)
				goto err;
			size *= 2;
			g_mount_params = p;
		}
		rc = read(fd, g_mount_params+off, size-off-1);
		if (rc < 0)
			goto err;
		off += rc;
		g_mount_params[off] = 0;
	} while (rc > 0);
out:
	if (fd >= 0)
		close(fd);
	printf("%s", g_mount_params);
	return;
err:
	free(g_mount_params);
	g_mount_params = NULL;
	goto out;
}

/* Dumb string search in the buffer */
enum {PARAM_FLAG, PARAM_STRING, PARAM_U32, PARAM_U64};
int param_type(const char *name)
{
	char needle[128] = {0};
	snprintf(needle, sizeof(needle)-1, "\n%s:", name);

	char *p = strstr(g_mount_params, needle);
	if (!p)
		return -1;
	p = strchr(p, ':');
	if (!p)
		return -1;
	if (!*p || !*(p+1) || !*(p+2))
		return -1;

	char *beg = p+1;
	char *end = strchr(beg, '\n');

	if (strncmp(beg, "flag", end-beg) == 0)
		return PARAM_FLAG;
	if (strncmp(beg, "noflag", end-beg) == 0)
		return PARAM_FLAG;
	if (strncmp(beg, "string", end-beg) == 0)
		return PARAM_STRING;
	if (strncmp(beg, "u32", end-beg) == 0)
		return PARAM_U32;
	if (strncmp(beg, "u64", end-beg) == 0)
		return PARAM_U64;
	return -1;
}

int main(void)
{
	int sfd;
	int mfd;

	/*
	 * Test param type detection
	 */
	read_mount_params();
	ASSERT(param_type("non-existing") < 0);
	ASSERT(param_type("ip") == PARAM_STRING);
	ASSERT(param_type("max_channels") == PARAM_U32);
	ASSERT(param_type("mfsymlinks") == PARAM_FLAG);
	ASSERT(param_type("nodfs") == PARAM_FLAG);
	ASSERT(param_type("user_xattr") == PARAM_FLAG);
	ASSERT(param_type("prefixpath") == PARAM_STRING);

	/*
	 * Converting following old-style mount syscall to new mount api
	 *
	 *   mount(
	 *     "//192.168.2.110/data",
	 *     "/mnt/test",
	 *     "cifs",
	 *     0,
	 *     "ip=192.168.2.110,unc=\\\\192.168.2.110\\data,vers=3.0,user=administrator,pass=my-pass"
	 *   )
	 *
	 */

	CHECK(sfd = fsopen("cifs", 0));
	CHECK_AND_LOG(sfd, fsconfig(sfd, FSCONFIG_SET_STRING, "source", "//192.168.2.110/data", 0));
	CHECK_AND_LOG(sfd, fsconfig(sfd, FSCONFIG_SET_STRING, "ip", "192.168.2.110", 0));
	CHECK_AND_LOG(sfd, fsconfig(sfd, FSCONFIG_SET_STRING, "unc", "\\\\192.168.2.110\\data", 0));
	CHECK_AND_LOG(sfd, fsconfig(sfd, FSCONFIG_SET_STRING, "vers", "3.0", 0));
	CHECK_AND_LOG(sfd, fsconfig(sfd, FSCONFIG_SET_STRING, "user", "administrator", 0));
	CHECK_AND_LOG(sfd, fsconfig(sfd, FSCONFIG_SET_STRING, "pass", "my-pass", 0));
	CHECK_AND_LOG(sfd, fsconfig(sfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0));
	CHECK_AND_LOG(sfd, (mfd = fsmount(sfd, FSMOUNT_CLOEXEC, 0)));
	CHECK(move_mount(mfd, "", AT_FDCWD, "/mnt/test", MOVE_MOUNT_F_EMPTY_PATH));
	return 0;
}