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mount_lookup.c
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mount_lookup.c
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#include <mntent.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
static char *read_overlay_mount_opt(struct mntent *cur_mount,
const char *opt_name) {
char *opt;
if ((opt = hasmntopt(cur_mount, opt_name))) {
if ((opt = strchr(opt, '='))) {
if (opt[0] == '.') {
// We cannot work with relative paths
return NULL;
}
char *opt_end = strchr(opt, ',');
if (opt_end) {
return strndup(opt + 1, opt_end - opt - 1);
}
return strdup(opt + 1);
}
}
return NULL;
}
static int match_overlay_mount_opts(struct mntent *cur_mount,
const char *opt_name, const char *opt_val) {
char *opt;
if ((opt = hasmntopt(cur_mount, opt_name))) {
if ((opt = strchr(opt, '='))) {
char *opt_end = strchr(opt, ',');
size_t opt_len;
if (opt_end) {
opt_len = opt_end - opt - 1;
} else {
opt_len = strlen(opt + 1);
}
if (strncmp(opt + 1, opt_val, opt_len) == 0) {
return 1;
}
}
}
return 0;
}
int sqmnt_lookup_mount_mountpoint(const char *mountpoint,
char **overlay_upper_dir,
char **overlay_lower_dir,
char **overlay_work_dir,
char **squashfs_device) {
struct mntent *cur_mount;
FILE *proc_mounts_fp = setmntent("/proc/mounts", "r");
*overlay_upper_dir = NULL;
*overlay_lower_dir = NULL;
*overlay_work_dir = NULL;
*squashfs_device = NULL;
// First: find the overlayfs entry
while ((cur_mount = getmntent(proc_mounts_fp))) {
if (strcmp(cur_mount->mnt_dir, mountpoint) == 0 &&
strcmp(cur_mount->mnt_fsname, "overlay") == 0) {
*overlay_lower_dir = read_overlay_mount_opt(cur_mount, "lowerdir");
*overlay_upper_dir = read_overlay_mount_opt(cur_mount, "upperdir");
*overlay_work_dir = read_overlay_mount_opt(cur_mount, "workdir");
// TODO handle failure of read_overlay_opt() here
break;
}
}
if (!(*overlay_upper_dir && *overlay_lower_dir && *overlay_work_dir)) {
goto fail;
}
// find the corresponding squashfs mount
rewind(proc_mounts_fp);
while ((cur_mount = getmntent(proc_mounts_fp))) {
if (strcmp(cur_mount->mnt_dir, *overlay_lower_dir) == 0 &&
strcmp(cur_mount->mnt_type, "squashfs") == 0) {
*squashfs_device = strdup(cur_mount->mnt_fsname);
}
}
if (*squashfs_device) {
endmntent(proc_mounts_fp);
return 0;
}
return 0;
fail:
endmntent(proc_mounts_fp);
free(*overlay_upper_dir);
free(*overlay_lower_dir);
free(*overlay_work_dir);
return -1;
}
int sqmnt_lookup_all_mounts(FILE *ptr, char **mount_point,
char **overlay_upper_dir, char **overlay_lower_dir,
char **overlay_work_dir, char **loop_device) {
*mount_point = NULL;
*overlay_upper_dir = NULL;
*overlay_lower_dir = NULL;
*overlay_work_dir = NULL;
*loop_device = NULL;
fpos_t last_squashfs_pos;
struct mntent *squashfs_mount;
// iterate over all squashfs mounts
while ((squashfs_mount = getmntent(ptr))) {
if (strcmp(squashfs_mount->mnt_type, "squashfs") == 0) {
*overlay_lower_dir = strdup(squashfs_mount->mnt_dir);
*loop_device = strdup(squashfs_mount->mnt_fsname);
// iterate over all other mounts looking for an overlay
fgetpos(ptr, &last_squashfs_pos);
struct mntent *overlay_mount;
while ((overlay_mount = getmntent(ptr))) {
if (strcmp(overlay_mount->mnt_type, "overlay") == 0 &&
match_overlay_mount_opts(overlay_mount, "lowerdir",
*overlay_lower_dir)) {
*mount_point = strdup(overlay_mount->mnt_dir);
*overlay_upper_dir =
read_overlay_mount_opt(overlay_mount, "upperdir");
*overlay_work_dir = read_overlay_mount_opt(overlay_mount, "workdir");
break;
}
}
if (*mount_point && *overlay_upper_dir && *overlay_lower_dir &&
*overlay_work_dir) {
return 1;
} else {
fsetpos(ptr, &last_squashfs_pos);
free(*mount_point);
free(*overlay_upper_dir);
free(*overlay_lower_dir);
free(*overlay_work_dir);
free(*loop_device);
*mount_point = NULL;
*overlay_upper_dir = NULL;
*overlay_lower_dir = NULL;
*overlay_work_dir = NULL;
*loop_device = NULL;
}
}
}
return 0;
}