Magisk/jni/utils/img.c

/* img.c - All image related functions
 */

#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/mount.h>
#include <linux/loop.h>

#include "magisk.h"
#include "utils.h"

static int e2fsck(const char *img) {
	// Check and repair ext4 image
	char buffer[128];
	int pid, fd = -1;
	pid = exec_command(1, &fd, NULL, "e2fsck", "-yf", img, NULL);
	if (pid < 0)
		return 1;
	while (fdgets(buffer, sizeof(buffer), fd))
		LOGD("magisk_img: %s", buffer);
	waitpid(pid, NULL, 0);
	close(fd);
	return 0;
}

static char *loopsetup(const char *img) {
	char device[20];
	struct loop_info64 info;
	int i, lfd, ffd;
	memset(&info, 0, sizeof(info));
	// First get an empty loop device
	for (i = 0; i <= 7; ++i) {
		sprintf(device, "/dev/block/loop%d", i);
		lfd = xopen(device, O_RDWR);
		if (ioctl(lfd, LOOP_GET_STATUS64, &info) == -1)
			break;
		close(lfd);
	}
	if (i == 8) return NULL;
	ffd = xopen(img, O_RDWR);
	if (ioctl(lfd, LOOP_SET_FD, ffd) == -1)
		return NULL;
	strcpy((char *) info.lo_file_name, img);
	ioctl(lfd, LOOP_SET_STATUS64, &info);
	close(lfd);
	close(ffd);
	return strdup(device);
}

int create_img(const char *img, int size) {
	unlink(img);
	LOGI("Create %s with size %dM\n", img, size);
	// Create a temp file with the file contexts
	char file_contexts[] = "/magisk(/.*)? u:object_r:system_file:s0\n";
	// If not root, attempt to create in current diretory
	char *filename = getuid() == UID_ROOT ? "/dev/file_contexts_image" : "file_contexts_image";
	int ret, fd = xopen(filename, O_WRONLY | O_CREAT | O_TRUNC, 0644);
	xwrite(fd, file_contexts, sizeof(file_contexts));
	close(fd);

	char buffer[16];
	snprintf(buffer, sizeof(buffer), "%dM", size);
	ret = exec_command_sync("make_ext4fs", "-l", buffer, "-a", "/magisk", "-S", filename, img, NULL);
	if (ret < 0)
		return 1;
	unlink(filename);
	return ret;
}

int get_img_size(const char *img, int *used, int *total) {
	if (access(img, R_OK) == -1)
		return 1;
	char buffer[PATH_MAX];
	int pid, fd = -1, status = 1;
	pid = exec_command(1, &fd, NULL, "e2fsck", "-n", img, NULL);
	if (pid < 0)
		return 1;
	while (fdgets(buffer, sizeof(buffer), fd)) {
		if (strstr(buffer, img)) {
			char *tok = strtok(buffer, ",");
			while(tok != NULL) {
				if (strstr(tok, "blocks")) {
					status = 0;
					break;
				}
				tok = strtok(NULL, ",");
			}
			if (status) continue;
			sscanf(tok, "%d/%d", used, total);
			*used = *used / 256 + 1;
			*total /= 256;
			break;
		}
	}
	close(fd);
	waitpid(pid, NULL, 0);
	return 0;
}

int resize_img(const char *img, int size) {
	LOGI("Resize %s to %dM\n", img, size);
	if (e2fsck(img))
		return 1;
	char buffer[128];
	int pid, status, fd = -1;
	snprintf(buffer, sizeof(buffer), "%dM", size);
	pid = exec_command(1, &fd, NULL, "resize2fs", img, buffer, NULL);
	if (pid < 0)
		return 1;
	while (fdgets(buffer, sizeof(buffer), fd))
		LOGD("magisk_img: %s", buffer);
	close(fd);
	waitpid(pid, &status, 0);
	return WEXITSTATUS(status);
}

char *mount_image(const char *img, const char *target) {
	if (access(img, F_OK) == -1)
		return NULL;
	if (access(target, F_OK) == -1) {
		if (xmkdir(target, 0755) == -1) {
			xmount(NULL, "/", NULL, MS_REMOUNT, NULL);
			xmkdir(target, 0755);
			xmount(NULL, "/", NULL, MS_REMOUNT | MS_RDONLY, NULL);
		}
	}

	if (e2fsck(img))
		return NULL;

	char *device = loopsetup(img);
	if (device)
		xmount(device, target, "ext4", 0, NULL);
	return device;
}

void umount_image(const char *target, const char *device) {
	xumount(target);
	int fd = xopen(device, O_RDWR);
	ioctl(fd, LOOP_CLR_FD);
	close(fd);
}

int merge_img(const char *source, const char *target) {
	if (access(source, F_OK) == -1)
		return 0;
	if (access(target, F_OK) == -1) {
		rename(source, target);
		return 0;
	}

	char buffer[PATH_MAX];

	// resize target to worst case
	int s_used, s_total, t_used, t_total, n_total;
	get_img_size(source, &s_used, &s_total);
	get_img_size(target, &t_used, &t_total);
	n_total = round_size(s_used + t_used);
	if (n_total != t_total)
		resize_img(target, n_total);

	xmkdir(SOURCE_TMP, 0755);
	xmkdir(TARGET_TMP, 0755);
	char *s_loop, *t_loop;
	s_loop = mount_image(source, SOURCE_TMP);
	if (s_loop == NULL) return 1;
	t_loop = mount_image(target, TARGET_TMP);
	if (t_loop == NULL) return 1;

	DIR *dir;
	struct dirent *entry;
	if (!(dir = opendir(SOURCE_TMP)))
		return 1;
	while ((entry = xreaddir(dir))) {
		if (entry->d_type == DT_DIR) {
			if (strcmp(entry->d_name, ".") == 0 ||
				strcmp(entry->d_name, "..") == 0 ||
				strcmp(entry->d_name, ".core") == 0 ||
				strcmp(entry->d_name, "lost+found") == 0)
				continue;
			// Cleanup old module if exists
			snprintf(buffer, sizeof(buffer), "%s/%s", TARGET_TMP, entry->d_name);
			if (access(buffer, F_OK) == 0) {
				LOGI("Upgrade module: %s\n", entry->d_name);
				exec_command_sync(BBPATH "/rm", "-rf", buffer, NULL);
			} else {
				LOGI("New module: %s\n", entry->d_name);
			}
		}
	}
	closedir(dir);
	cp_afc(SOURCE_TMP, TARGET_TMP);

	// Unmount all loop devices
	umount_image(SOURCE_TMP, s_loop);
	umount_image(TARGET_TMP, t_loop);
	rmdir(SOURCE_TMP);
	rmdir(TARGET_TMP);
	free(s_loop);
	free(t_loop);
	unlink(source);
	return 0;
}

void trim_img(const char *img) {
	int used, total, new_size;
	get_img_size(img, &used, &total);
	new_size = round_size(used);
	if (new_size != total)
		resize_img(img, new_size);
}