#include <sys/param.h>
#include <sys/mount.h>
#include <sys/statvfs.h>

SInt64 get_root_avail_capacity(void)
{
    CFURLRef root = CFURLCreateWithFileSystemPath(NULL, CFSTR("/"), kCFURLPOSIXPathStyle, YES);
    CFErrorRef err = NULL;
    CFTypeRef ref;
    SInt64 val = -1;
    Boolean ok;

    if (root == NULL) goto out_exit;

    ok = CFURLCopyResourcePropertyForKey(root, kCFURLVolumeAvailableCapacityKey, &ref, &err);
    if (ok) {
        assert(CFGetTypeID(ref) == CFNumberGetTypeID());
        assert(CFNumberGetType(ref) == kCFNumberSInt64Type);
        ok = CFNumberGetValue((CFNumberRef) ref, kCFNumberSInt64Type, &val);
        assert(ok);
        CFRelease(ref);
    } else {
        assert(err != NULL);
        NSLog(@"[ERR] CFURLCopyResourcePropertyForKey() fail  err: %@", err);
        CFRelease(err);
    }

    CFRelease(root);
out_exit:
    return val;
}

int64_t get_root_avail_capacity2(void)
{
    int64_t sz = -1;
    struct statvfs v;

    (void) memset(&v, 0, sizeof(v));

    if (statvfs("/", &v) != 0) {
        fprintf(stderr, "statvfs(3) fail  errno: %d\n", errno);
        goto out_exit;
    } else if (v.f_bavail <= 0 || v.f_frsize <= 0) {
        goto out_exit;
    }

    sz = v.f_bavail * v.f_frsize;
out_exit:
    return sz;
}

int64_t get_root_avail_capacity3(void)
{
    int64_t sz = -1;
    struct statfs v;

    (void) memset(&v, 0, sizeof(v));

    if (statfs("/", &v) != 0) {
        fprintf(stderr, "statfs(2) fail  errno: %d\n", errno);
        goto out_exit;
    } else if (v.f_bavail <= 0 || v.f_bsize <= 0) {
        goto out_exit;
    }

    sz = v.f_bavail * v.f_bsize;
out_exit:
    return sz;
}