rust-kernel

//! coretest -- stage 17, "coreutils batch 2": the system calls coreutils
//! and busybox use beyond what libctest (stage 16) covers. Run with one
//! group name; exit code = number of failed checks:
//!   links    link/linkat, symlink/symlinkat on ramfs and ext2; EPERM on
//!            FAT/exFAT, EROFS on btrfs; rename over a second hard link
//!   owners   chown/fchown/lchown/fchownat (stored, not enforced)
//!   statfs   statfs/fstatfs magic numbers and sizes, statx, st_dev
//!   info     sysinfo (99), times, getrusage, CPU clocks, clock_getres
//!   sockets  getsockname/getpeername, get/setsockopt, shutdown, socketpair
//!   timers   alarm, setitimer/getitimer, timer_create & co.
//!   ids      setuid & co., groups, priority, sethostname
//!   misc     flock, preadv/pwritev, sendfile, ppoll/pselect6 masks,
//!            getdents while deleting
#![no_std]
#![no_main]

#[macro_use]
#[path = "ulib.rs"]
mod ulib;

extern crate alloc;

use alloc::format;
use alloc::vec::Vec;
use core::sync::atomic::{AtomicI64, AtomicU64, Ordering};
use ulib::*;

// Stage 17 syscall numbers (Linux's).
const SYS_SHUTDOWN: u64 = 48;
const SYS_GETSOCKNAME: u64 = 51;
const SYS_GETPEERNAME: u64 = 52;
const SYS_SOCKETPAIR: u64 = 53;
const SYS_GETSOCKOPT: u64 = 55;
const SYS_GETITIMER: u64 = 36;
const SYS_ALARM: u64 = 37;
const SYS_SETITIMER: u64 = 38;
const SYS_SENDFILE: u64 = 40;
const SYS_FLOCK: u64 = 73;
const SYS_LINK: u64 = 86;
const SYS_SYMLINK: u64 = 88;
const SYS_CHOWN: u64 = 92;
const SYS_FCHOWN: u64 = 93;
const SYS_LCHOWN: u64 = 94;
const SYS_GETRUSAGE: u64 = 98;
const SYS_SYSINFO: u64 = 99;
const SYS_TIMES: u64 = 100;
const SYS_GETGID: u64 = 104;
const SYS_SETUID: u64 = 105;
const SYS_SETGID: u64 = 106;
const SYS_GETEUID: u64 = 107;
const SYS_SETREUID: u64 = 113;
const SYS_GETGROUPS: u64 = 115;
const SYS_SETGROUPS: u64 = 116;
const SYS_SETRESUID: u64 = 117;
const SYS_GETRESUID: u64 = 118;
const SYS_GETRESGID: u64 = 120;
const SYS_STATFS: u64 = 137;
const SYS_FSTATFS: u64 = 138;
const SYS_GETPRIORITY: u64 = 140;
const SYS_SETPRIORITY: u64 = 141;
const SYS_SETHOSTNAME: u64 = 170;
const SYS_TIMER_CREATE: u64 = 222;
const SYS_TIMER_SETTIME: u64 = 223;
const SYS_TIMER_GETTIME: u64 = 224;
const SYS_TIMER_GETOVERRUN: u64 = 225;
const SYS_TIMER_DELETE: u64 = 226;
const SYS_CLOCK_GETRES: u64 = 229;
const SYS_FCHOWNAT: u64 = 260;
const SYS_LINKAT: u64 = 265;
const SYS_SYMLINKAT: u64 = 266;
const SYS_PSELECT6: u64 = 270;
const SYS_PREADV: u64 = 295;
const SYS_PWRITEV: u64 = 296;
const SYS_STATX: u64 = 332;

const AT_FDCWD: i64 = -100;
const AT_SYMLINK_NOFOLLOW: u64 = 0x100;
const AT_SYMLINK_FOLLOW: u64 = 0x400;
const AT_EMPTY_PATH: u64 = 0x1000;
const O_RDWR: u64 = 2;
const EROFS: i64 = 30;
const EMLINK_OR_EPERM: [i64; 2] = [EPERM, 31];
const EACCES: i64 = 13;
const ENOTCONN: i64 = 107;
const ECONNREFUSED: i64 = 111;
const ENOPROTOOPT: i64 = 92;
const EAFNOSUPPORT: i64 = 97;
const EPIPE: i64 = 32;
const SIGALRM: i32 = 14;

fn cpath(s: &str) -> Vec<u8> {
    let mut v = Vec::from(s.as_bytes());
    v.push(0);
    v
}

fn p2(nr: u64, a: &str, b: &str) -> i64 {
    let (a, b) = (cpath(a), cpath(b));
    syscall3(nr, a.as_ptr() as u64, b.as_ptr() as u64, 0)
}

fn write_file(path: &str, data: &[u8]) -> i64 {
    let fd = open(path, O_WRONLY | O_CREAT | O_TRUNC);
    if fd < 0 {
        return fd;
    }
    let n = write(fd, data);
    close(fd);
    n
}

fn read_file(path: &str) -> Vec<u8> {
    let fd = open(path, O_RDONLY);
    let mut out = Vec::new();
    if fd < 0 {
        return out;
    }
    let mut buf = [0u8; 512];
    loop {
        let n = read(fd, &mut buf);
        if n <= 0 {
            break;
        }
        out.extend_from_slice(&buf[..n as usize]);
    }
    close(fd);
    out
}

fn st(path: &str) -> Stat {
    let mut s = Stat::default();
    if stat(path, &mut s) < 0 {
        s.ino = 0;
        s.nlink = 0;
    }
    s
}

fn lst(path: &str) -> Stat {
    let mut s = Stat::default();
    lstat(path, &mut s);
    s
}

/// Burn CPU in user mode for `ms` (looking at the clock only now and then,
/// so it's nearly all user time).
fn spin_ms(ms: u64) {
    let end = now_us() + ms * 1000;
    let mut x = 0u64;
    while now_us() < end {
        for _ in 0..200_000 {
            x = core::hint::black_box(x.wrapping_mul(31).wrapping_add(7));
        }
    }
}

fn main() -> i64 {
    let group = arg(1).unwrap_or("");
    let mut c = Checks::new("coretest");
    match group {
        "links" => links(&mut c),
        "owners" => owners(&mut c),
        "statfs" => statfs(&mut c),
        "info" => info(&mut c),
        "sockets" => sockets(&mut c),
        "timers" => timers(&mut c),
        "ids" => ids(&mut c),
        "misc" => misc(&mut c),
        _ => c.check(false, "usage: coretest links|owners|statfs|info|sockets|timers|ids|misc"),
    }
    c.done()
}

// --- links ---------------------------------------------------------------------

fn links_on(c: &mut Checks, dir: &str) {
    let (a, b, l, d) = (format!("{}/a.txt", dir), format!("{}/b.txt", dir), format!("{}/l", dir), format!("{}/d", dir));
    unlink(&a);
    unlink(&b);
    unlink(&l);
    rmdir(&d);
    write_file(&a, b"hello");
    c.check(p2(SYS_LINK, &a, &b) == 0, &format!("{}: link a.txt b.txt", dir));
    let (sa, sb) = (st(&a), st(&b));
    c.check(sa.ino == sb.ino && sa.ino != 0, &format!("{}: both names, one inode number", dir));
    c.check(sa.nlink == 2 && sb.nlink == 2, &format!("{}: st_nlink is 2", dir));
    let fd = open(&b, O_WRONLY);
    lseek(fd, 0, 2);
    write(fd, b" world");
    close(fd);
    c.check(read_file(&a) == b"hello world", &format!("{}: a write through one name shows through the other", dir));
    c.check(p2(SYS_LINK, &a, &b) == -EEXIST, &format!("{}: link onto an existing name: EEXIST", dir));
    // rename onto another hard link of the same file: nothing happens (POSIX).
    c.check(rename(&a, &b) == 0 && st(&a).nlink == 2 && st(&b).nlink == 2, &format!("{}: rename a.txt over its own link b.txt: both stay", dir));
    c.check(unlink(&a) == 0 && st(&b).nlink == 1 && read_file(&b) == b"hello world", &format!("{}: unlink one name, the data stays", dir));
    // symlinks
    c.check(p2(SYS_SYMLINK, "b.txt", &l) == 0, &format!("{}: symlink b.txt l", dir));
    let mut buf = [0u8; 64];
    let n = readlink(&l, &mut buf);
    c.check(n == 5 && &buf[..5] == b"b.txt", &format!("{}: readlink gives the target as written", dir));
    c.check(lst(&l).is_symlink() && st(&l).is_file() && st(&l).ino == st(&b).ino, &format!("{}: lstat sees the link, stat the file", dir));
    c.check(read_file(&l) == b"hello world", &format!("{}: open follows the symlink", dir));
    c.check(p2(SYS_SYMLINK, "x", &l) == -EEXIST, &format!("{}: symlink onto an existing name: EEXIST", dir));
    // linkat: the symlink itself, or (AT_SYMLINK_FOLLOW) what it points to.
    let (l2, l3) = (format!("{}/l2", dir), format!("{}/l3", dir));
    let (cl, cl2, cl3) = (cpath(&l), cpath(&l2), cpath(&l3));
    let r = syscall5(SYS_LINKAT, AT_FDCWD as u64, cl.as_ptr() as u64, AT_FDCWD as u64, cl2.as_ptr() as u64, 0);
    c.check(r == 0 && lst(&l2).is_symlink(), &format!("{}: linkat without FOLLOW links the symlink itself", dir));
    let r = syscall5(SYS_LINKAT, AT_FDCWD as u64, cl.as_ptr() as u64, AT_FDCWD as u64, cl3.as_ptr() as u64, AT_SYMLINK_FOLLOW);
    c.check(r == 0 && lst(&l3).is_file() && st(&b).nlink == 2, &format!("{}: linkat AT_SYMLINK_FOLLOW links the file", dir));
    // symlinkat relative to a directory fd; a dangling one is fine.
    mkdir(&d);
    let dfd = open(&d, O_RDONLY | O_DIRECTORY);
    let (t, name) = (cpath("../nowhere"), cpath("dangling"));
    c.check(syscall3(SYS_SYMLINKAT, t.as_ptr() as u64, dfd as u64, name.as_ptr() as u64) == 0, &format!("{}: symlinkat(dirfd) makes a dangling link", dir));
    c.check(lst(&format!("{}/dangling", d)).is_symlink() && open(&format!("{}/dangling", d), O_RDONLY) == -ENOENT, &format!("{}: ...which lstat sees and open can't follow", dir));
    close(dfd);
    c.check(p2(SYS_LINK, &d, &format!("{}/dlink", dir)) == -EPERM, &format!("{}: hard link to a directory: EPERM", dir));
    // A directory moved into another one (native rename).
    let e = format!("{}/e", dir);
    rmdir(&e);
    mkdir(&e);
    c.check(rename(&d, &format!("{}/d", e)) == 0 && lst(&format!("{}/d/dangling", e)).is_symlink(), &format!("{}: rename moves a full directory", dir));
    // A long target (ext2 keeps short ones in the inode, long ones in a block).
    let long: alloc::string::String = core::iter::repeat('x').take(100).collect();
    let ll = format!("{}/long", dir);
    unlink(&ll);
    c.check(p2(SYS_SYMLINK, &long, &ll) == 0 && readlink(&ll, &mut [0u8; 200]) == 100, &format!("{}: a 100-byte symlink target", dir));
    // clean up
    for f in [&b, &l, &l2, &l3, &ll, &format!("{}/d/dangling", e)] {
        unlink(f);
    }
    rmdir(&format!("{}/d", e));
    rmdir(&e);
    c.check(access(&b) == -ENOENT && access(&e) == -ENOENT, &format!("{}: all cleaned up", dir));
}

fn links(c: &mut Checks) {
    mkdir("/tmp/lk");
    links_on(c, "/tmp/lk");
    rmdir("/tmp/lk");
    mkdir("/mnt/disk1/lk");
    links_on(c, "/mnt/disk1/lk");
    rmdir("/mnt/disk1/lk");
    // Across file systems: EXDEV.
    write_file("/tmp/x.txt", b"x");
    c.check(p2(SYS_LINK, "/tmp/x.txt", "/mnt/disk1/x.txt") == -EXDEV, "link across file systems: EXDEV");
    unlink("/tmp/x.txt");
    // FAT and exFAT have no links on disk; btrfs is mounted read-only.
    write_file("/mnt/disk0/lk.txt", b"x");
    c.check(EMLINK_OR_EPERM.contains(&-p2(SYS_LINK, "/mnt/disk0/lk.txt", "/mnt/disk0/lk2.txt")), "FAT: link is EPERM");
    c.check(p2(SYS_SYMLINK, "lk.txt", "/mnt/disk0/lk3") == -EPERM, "FAT: symlink is EPERM");
    unlink("/mnt/disk0/lk.txt");
    write_file("/mnt/disk2/lk.txt", b"x");
    c.check(p2(SYS_SYMLINK, "lk.txt", "/mnt/disk2/lk3") == -EPERM, "exFAT: symlink is EPERM");
    unlink("/mnt/disk2/lk.txt");
    c.check(p2(SYS_LINK, "/mnt/disk3/hello.txt", "/mnt/disk3/h2") == -EROFS, "btrfs: link is EROFS");
    c.check(p2(SYS_SYMLINK, "hello.txt", "/mnt/disk3/h3") == -EROFS, "btrfs: symlink is EROFS");
    let s = st("/mnt/disk3/hello.txt");
    c.check(s.nlink >= 1 && s.ino != 0, "btrfs: stat shows the real link count and inode");
}

// --- owners --------------------------------------------------------------------

fn chown(nr: u64, path: &str, uid: u32, gid: u32) -> i64 {
    let p = cpath(path);
    syscall3(nr, p.as_ptr() as u64, uid as u64, gid as u64)
}

fn owners(c: &mut Checks) {
    for dir in ["/tmp", "/mnt/disk1"] {
        let (f, l) = (format!("{}/own.txt", dir), format!("{}/own.lnk", dir));
        unlink(&f);
        unlink(&l);
        write_file(&f, b"x");
        p2(SYS_SYMLINK, "own.txt", &l);
        c.check(chown(SYS_CHOWN, &f, 1000, 100) == 0, &format!("{}: chown 1000:100", dir));
        let s = st(&f);
        c.check(s.uid == 1000 && s.gid == 100, &format!("{}: stat shows 1000:100", dir));
        c.check(chown(SYS_CHOWN, &f, u32::MAX, 50) == 0 && st(&f).uid == 1000 && st(&f).gid == 50, &format!("{}: -1 leaves the uid alone", dir));
        c.check(chown(SYS_LCHOWN, &l, 7, 7) == 0 && lst(&l).uid == 7 && st(&f).uid == 1000, &format!("{}: lchown changes the link, not the file", dir));
        c.check(chown(SYS_CHOWN, &l, 8, 8) == 0 && st(&f).uid == 8 && lst(&l).uid == 7, &format!("{}: chown through a link changes the file", dir));
        let fd = open(&f, O_RDONLY);
        c.check(syscall3(SYS_FCHOWN, fd as u64, 9, 9) == 0 && st(&f).uid == 9, &format!("{}: fchown", dir));
        let empty = cpath("");
        let r = syscall5(SYS_FCHOWNAT, fd as u64, empty.as_ptr() as u64, 0, 0, AT_EMPTY_PATH);
        c.check(r == 0 && st(&f).uid == 0, &format!("{}: fchownat(fd, \"\", AT_EMPTY_PATH)", dir));
        close(fd);
        let name = cpath("own.lnk");
        let dfd = open(dir, O_RDONLY | O_DIRECTORY);
        let r = syscall5(SYS_FCHOWNAT, dfd as u64, name.as_ptr() as u64, 3, 3, AT_SYMLINK_NOFOLLOW);
        c.check(r == 0 && lst(&l).uid == 3 && st(&f).uid == 0, &format!("{}: fchownat(dirfd, AT_SYMLINK_NOFOLLOW)", dir));
        close(dfd);
        unlink(&f);
        unlink(&l);
    }
    // Directories too.
    mkdir("/tmp/ownd");
    c.check(chown(SYS_CHOWN, "/tmp/ownd", 5, 6) == 0 && st("/tmp/ownd").uid == 5, "chown a directory");
    rmdir("/tmp/ownd");
    // FAT: no owners on disk. Root:root (what it shows) is fine, anything else EPERM.
    write_file("/mnt/disk0/own.txt", b"x");
    c.check(chown(SYS_CHOWN, "/mnt/disk0/own.txt", 0, 0) == 0, "FAT: chown to 0:0 (no change) succeeds");
    c.check(chown(SYS_CHOWN, "/mnt/disk0/own.txt", 1000, 1000) == -EPERM, "FAT: chown to 1000 is EPERM");
    unlink("/mnt/disk0/own.txt");
    write_file("/mnt/disk2/own.txt", b"x");
    c.check(chown(SYS_CHOWN, "/mnt/disk2/own.txt", 1000, u32::MAX) == -EPERM, "exFAT: chown to 1000 is EPERM");
    unlink("/mnt/disk2/own.txt");
    c.check(chown(SYS_CHOWN, "/mnt/disk3/hello.txt", 1, 1) == -EROFS, "btrfs: chown is EROFS");
    c.check(chown(SYS_CHOWN, "/tmp/missing", 1, 1) == -ENOENT, "chown of a missing file: ENOENT");
    // Pipes: nothing to own, accepted.
    let (r, w) = pipe().unwrap();
    c.check(syscall3(SYS_FCHOWN, r as u64, 1, 1) == 0, "fchown on a pipe: accepted");
    close(r);
    close(w);
}

// --- statfs / statx --------------------------------------------------------------

fn statfs_of(path: &str) -> (i64, [u64; 15]) {
    let mut buf = [0u64; 15];
    let p = cpath(path);
    (syscall3(SYS_STATFS, p.as_ptr() as u64, buf.as_mut_ptr() as u64, 0), buf)
}

fn statfs(c: &mut Checks) {
    let cases: [(&str, u64, &str); 6] = [
        ("/", 0x8584_58f6, "ramfs"),
        ("/tmp", 0x8584_58f6, "ramfs"),
        ("/mnt/disk0", 0x4d44, "FAT (MSDOS_SUPER_MAGIC)"),
        ("/mnt/disk1/", 0xEF53, "ext2"),
        ("/mnt/disk2", 0x2011_BAB0, "exFAT"),
        ("/mnt/disk3/hello.txt", 0x9123_683E, "btrfs"),
    ];
    for (path, magic, what) in cases {
        let (r, b) = statfs_of(path);
        c.check(r == 0 && b[0] == magic, &format!("statfs {}: f_type = {}", path, what));
        if path.starts_with("/mnt") {
            c.check(b[1] >= 512 && b[2] > 0 && b[3] <= b[2] && b[4] <= b[3], &format!("statfs {}: sizes make sense (bsize {}, {} blocks, {} free)", path, b[1], b[2], b[3]));
            c.check(b[8] >= 255, &format!("statfs {}: f_namelen {}", path, b[8]));
        }
    }
    let (_, b) = statfs_of("/mnt/disk3");
    c.check(b[10] & 1 == 1, "btrfs: ST_RDONLY in f_flags");
    let (_, b) = statfs_of("/mnt/disk1");
    c.check(b[10] & 1 == 0 && b[5] > 0 && b[6] <= b[5], "ext2: writable, counts inodes");
    // Writing a file uses up free blocks on ext2.
    let (_, before) = statfs_of("/mnt/disk1");
    write_file("/mnt/disk1/sf.bin", &[7u8; 64 * 1024]);
    let (_, after) = statfs_of("/mnt/disk1");
    c.check(after[3] < before[3], "ext2: a 64 KiB file lowers f_bfree");
    unlink("/mnt/disk1/sf.bin");
    c.check(statfs_of("/nope").0 == -ENOENT, "statfs of a missing path: ENOENT");
    let fd = open("/mnt/disk0", O_RDONLY | O_DIRECTORY);
    let mut b = [0u64; 15];
    c.check(syscall3(SYS_FSTATFS, fd as u64, b.as_mut_ptr() as u64, 0) == 0 && b[0] == 0x4d44, "fstatfs on a FAT directory fd");
    close(fd);
    let (r, w) = pipe().unwrap();
    c.check(syscall3(SYS_FSTATFS, r as u64, b.as_mut_ptr() as u64, 0) == 0 && b[0] == 0x5049_5045, "fstatfs on a pipe: PIPEFS_MAGIC");
    close(r);
    close(w);
    // st_dev tells file systems apart.
    c.check(st("/tmp").dev != st("/mnt/disk1").dev && st("/mnt/disk1/").dev == st("/mnt/disk1/lost+found").dev, "st_dev: one per file system");
    // Stage 18 fix check (Clarke): a mount point itself reports the
    // *mounted* file system's st_dev and root inode, not the directory it
    // covers. find -xdev, du -x and cp -x compare st_dev with this.
    write_file("/tmp/devchk", b"x");
    c.check(st("/tmp").dev == st("/tmp/devchk").dev && st("/tmp").dev != st("/").dev, "stat(\"/tmp\"): the mounted ramfs's st_dev, not /'s");
    c.check(st("/dev").dev == st("/dev/null").dev && st("/dev").dev != st("/").dev, "stat(\"/dev\"): devfs's st_dev");
    c.check(st("/mnt/disk1").dev == st("/mnt/disk1/lost+found").dev && st("/mnt/disk1").ino == 2, "stat(\"/mnt/disk1\"): ext2's st_dev and its root inode (2)");
    let mut ls = Stat::default();
    c.check(lstat("/tmp", &mut ls) == 0 && ls.dev == st("/tmp/devchk").dev, "lstat of a mount point: the mounted fs's st_dev too");
    let fd = open("/mnt/disk1", O_RDONLY | O_DIRECTORY);
    let mut fs_ = Stat::default();
    c.check(fstat(fd, &mut fs_) == 0 && fs_.dev == st("/mnt/disk1/lost+found").dev && fs_.ino == 2, "fstat of an fd opened on a mount point: same");
    close(fd);
    unlink("/tmp/devchk");
    // statx
    write_file("/tmp/sx.txt", b"twelve bytes");
    let mut sx = [0u8; 256];
    let p = cpath("/tmp/sx.txt");
    let r = syscall5(SYS_STATX, AT_FDCWD as u64, p.as_ptr() as u64, 0, 0x7ff, sx.as_mut_ptr() as u64);
    let u32at = |b: &[u8], o: usize| u32::from_le_bytes(b[o..o + 4].try_into().unwrap());
    let u64at = |b: &[u8], o: usize| u64::from_le_bytes(b[o..o + 8].try_into().unwrap());
    let s = st("/tmp/sx.txt");
    c.check(r == 0 && u32at(&sx, 0) & 0x7ff == 0x7ff, "statx: basic fields in stx_mask");
    c.check(u64at(&sx, 40) == 12 && u64at(&sx, 32) == s.ino && u32at(&sx, 16) == 1, "statx: size, inode number, nlink match stat");
    c.check(u32::from(u16::from_le_bytes([sx[28], sx[29]])) == s.mode && u64at(&sx, 112) as i64 == s.mtime[0], "statx: mode and mtime match stat");
    c.check(u32at(&sx, 140) as u64 == s.dev, "statx: device minor = st_dev");
    let fd = open("/tmp/sx.txt", O_RDONLY);
    let empty = cpath("");
    let r = syscall5(SYS_STATX, fd as u64, empty.as_ptr() as u64, AT_EMPTY_PATH, 0x7ff, sx.as_mut_ptr() as u64);
    c.check(r == 0 && u64at(&sx, 40) == 12, "statx(fd, \"\", AT_EMPTY_PATH)");
    close(fd);
    let r = syscall5(SYS_STATX, AT_FDCWD as u64, p.as_ptr() as u64, 0x4, 0x7ff, sx.as_mut_ptr() as u64);
    c.check(r == -EINVAL, "statx with an unknown flag: EINVAL");
    p2(SYS_SYMLINK, "sx.txt", "/tmp/sx.lnk");
    let pl = cpath("/tmp/sx.lnk");
    syscall5(SYS_STATX, AT_FDCWD as u64, pl.as_ptr() as u64, AT_SYMLINK_NOFOLLOW, 0x7ff, sx.as_mut_ptr() as u64);
    c.check(u32::from(u16::from_le_bytes([sx[28], sx[29]])) & S_IFMT == S_IFLNK, "statx AT_SYMLINK_NOFOLLOW: the link itself");
    unlink("/tmp/sx.lnk");
    unlink("/tmp/sx.txt");
}

// --- info: sysinfo, times, getrusage, clocks ---------------------------------------

fn clock_ns(clock: u64) -> (i64, u64) {
    let mut ts = [0u64; 2];
    let r = syscall3(SYS_CLOCK_GETTIME, clock, ts.as_mut_ptr() as u64, 0);
    (r, ts[0] * 1_000_000_000 + ts[1])
}

fn info(c: &mut Checks) {
    let mut si = [0u64; 14];
    c.check(syscall3(SYS_SYSINFO, si.as_mut_ptr() as u64, 0, 0) == 0, "sysinfo (99): 0");
    let procs = si[10] & 0xffff;
    let mem_unit = si[13] & 0xffff_ffff;
    c.check(si[0] > 0 && si[4] > si[5] && si[5] > 0, "sysinfo: uptime, totalram > freeram > 0");
    c.check(procs >= 1 && mem_unit == 1, "sysinfo: procs >= 1, mem_unit 1");
    c.check(sysinfo().cpus == 4, "Rustbelt's own sysinfo (502) still works");
    // CPU time: spin 300 ms, it shows up everywhere.
    let mut tms = [0u64; 4];
    let t0 = syscall3(SYS_TIMES, tms.as_mut_ptr() as u64, 0, 0);
    let (_, p0) = clock_ns(2);
    spin_ms(300);
    let t1 = syscall3(SYS_TIMES, tms.as_mut_ptr() as u64, 0, 0);
    c.check(t1 - t0 >= 25 && t1 - t0 <= 60, &format!("times: returns ticks (100/s): {} after 300 ms", t1 - t0));
    c.check(tms[0] + tms[1] >= 15, &format!("times: utime+stime {} ticks after spinning 300 ms", tms[0] + tms[1]));
    c.check(tms[0] >= tms[1], "times: spinning is mostly user time");
    let (r, p1) = clock_ns(2);
    c.check(r == 0 && p1 - p0 >= 150_000_000, "CLOCK_PROCESS_CPUTIME_ID advanced >= 150 ms");
    let (r, t) = clock_ns(3);
    c.check(r == 0 && t >= 150_000_000, "CLOCK_THREAD_CPUTIME_ID too");
    let mut ru = [0u64; 18];
    c.check(syscall3(SYS_GETRUSAGE, 0, ru.as_mut_ptr() as u64, 0) == 0, "getrusage(RUSAGE_SELF)");
    c.check(ru[0] * 1_000_000 + ru[1] >= 150_000 && ru[4] > 0, "getrusage: ru_utime >= 150 ms, ru_maxrss > 0");
    // Children's times count once they're reaped.
    let pid = fork();
    if pid == 0 {
        spin_ms(200);
        exit(0);
    }
    wait4(pid, 0).ok();
    syscall3(SYS_TIMES, tms.as_mut_ptr() as u64, 0, 0);
    c.check(tms[2] + tms[3] >= 10, &format!("times: the reaped child's {} ticks are in cutime+cstime", tms[2] + tms[3]));
    syscall3(SYS_GETRUSAGE, (-1i64) as u64, ru.as_mut_ptr() as u64, 0);
    c.check(ru[0] * 1_000_000 + ru[1] + ru[2] * 1_000_000 + ru[3] >= 100_000, "getrusage(RUSAGE_CHILDREN) has it too");
    c.check(syscall3(SYS_GETRUSAGE, 5, ru.as_mut_ptr() as u64, 0) == -EINVAL, "getrusage(5): EINVAL");
    let mut res = [0u64; 2];
    c.check(syscall3(SYS_CLOCK_GETRES, 1, res.as_mut_ptr() as u64, 0) == 0 && res == [0, 1000], "clock_getres(MONOTONIC): 1 µs");
    c.check(syscall3(SYS_CLOCK_GETRES, 2, res.as_mut_ptr() as u64, 0) == 0 && res == [0, 10_000_000], "clock_getres(PROCESS_CPUTIME): 10 ms");
    c.check(syscall3(SYS_CLOCK_GETRES, 0, 0, 0) == 0, "clock_getres with a NULL pointer: 0");
    c.check(syscall3(SYS_CLOCK_GETRES, 42, res.as_mut_ptr() as u64, 0) == -EINVAL, "clock_getres(42): EINVAL");
}

// --- sockets -----------------------------------------------------------------------

fn getsockopt_int(fd: i64, level: u64, opt: u64) -> (i64, u32) {
    let mut v = 0u32;
    let mut len = 4u32;
    let r = syscall5(SYS_GETSOCKOPT, fd as u64, level, opt, &mut v as *mut u32 as u64, &mut len as *mut u32 as u64);
    (r, v)
}

fn setsockopt_int(fd: i64, level: u64, opt: u64, v: u32) -> i64 {
    syscall5(SYS_SETSOCKOPT, fd as u64, level, opt, &v as *const u32 as u64, 4)
}

fn sockname(nr: u64, fd: i64) -> (i64, SockAddrIn) {
    let mut sa = SockAddrIn::default();
    let mut len = 16u32;
    let r = syscall3(nr, fd as u64, &mut sa as *mut _ as u64, &mut len as *mut u32 as u64);
    (r, sa)
}

fn sockets(c: &mut Checks) {
    sigaction_raw(13, 1, 0, 0); // SIGPIPE: SIG_IGN, so a write after shutdown is just EPIPE
    let srv = socket(SOCK_STREAM, 0);
    c.check(setsockopt_int(srv, 1, 2, 1) == 0, "setsockopt SO_REUSEADDR: 0 (was ENOPROTOOPT)");
    c.check(getsockopt_int(srv, 1, 2) == (0, 1), "getsockopt SO_REUSEADDR reads it back");
    c.check(setsockopt_int(srv, 1, 15, 1) == 0 && setsockopt_int(srv, 1, 9, 1) == 0, "SO_REUSEPORT, SO_KEEPALIVE: 0");
    c.check(setsockopt_int(srv, 6, 1, 1) == 0, "TCP_NODELAY: 0");
    c.check(setsockopt_int(srv, 1, 99, 1) == -ENOPROTOOPT, "an unknown option: ENOPROTOOPT");
    c.check(bind(srv, 7091) == 0 && listen(srv, 4) == 0, "bind 7091 + listen");
    let (r, sa) = sockname(SYS_GETSOCKNAME, srv);
    c.check(r == 0 && sa.port() == 7091 && sa.family == 2, "getsockname on the listener: port 7091");
    c.check(getsockopt_int(srv, 1, 30) == (0, 1), "SO_ACCEPTCONN: listening");
    c.check(sockname(SYS_GETPEERNAME, srv).0 == -ENOTCONN, "getpeername on a listener: ENOTCONN");
    let cl = socket(SOCK_STREAM, 0);
    c.check(syscall3(SYS_SHUTDOWN, cl as u64, 1, 0) == -ENOTCONN, "shutdown before connecting: ENOTCONN");
    c.check(connect(cl, Ip([127, 0, 0, 1]), 7091) == 0, "connect to 127.0.0.1:7091");
    let (conn, _) = accept(srv);
    c.check(conn >= 0, "accept");
    let (r, me) = sockname(SYS_GETSOCKNAME, cl);
    let (r2, peer) = sockname(SYS_GETPEERNAME, conn);
    c.check(r == 0 && r2 == 0 && me.addr == [127, 0, 0, 1] && me.port() == peer.port() && me.port() != 0, "client's getsockname = server's getpeername");
    let (_, p) = sockname(SYS_GETPEERNAME, cl);
    c.check(p.port() == 7091 && p.addr == [127, 0, 0, 1], "client's getpeername: 127.0.0.1:7091");
    c.check(getsockopt_int(cl, 1, 3) == (0, 1), "SO_TYPE: SOCK_STREAM");
    c.check(getsockopt_int(cl, 1, 4) == (0, 0), "SO_ERROR: 0");
    let (r, rcv) = getsockopt_int(cl, 1, 8);
    c.check(r == 0 && rcv > 0, "SO_RCVBUF > 0");
    // shutdown(SHUT_WR): the other side reads end-of-file, but can still answer.
    write(cl, b"ping");
    c.check(syscall3(SYS_SHUTDOWN, cl as u64, 1, 0) == 0, "shutdown(SHUT_WR)");
    let mut buf = [0u8; 16];
    let mut got = Vec::new();
    loop {
        let n = read(conn, &mut buf);
        if n <= 0 {
            c.check(n == 0, "server reads end-of-file after the data");
            break;
        }
        got.extend_from_slice(&buf[..n as usize]);
    }
    c.check(got == b"ping", "server got \"ping\"");
    c.check(write(cl, b"x") == -EPIPE, "client write after SHUT_WR: EPIPE");
    write(conn, b"pong");
    let n = read(cl, &mut buf);
    c.check(n == 4 && &buf[..4] == b"pong", "client still reads the answer");
    close(conn);
    close(cl);
    close(srv);
    // UDP
    let u = socket(SOCK_DGRAM, 0);
    c.check(getsockopt_int(u, 1, 3) == (0, 2), "UDP: SO_TYPE is SOCK_DGRAM");
    bind(u, 7092);
    c.check(sockname(SYS_GETSOCKNAME, u).1.port() == 7092, "UDP getsockname: 7092");
    close(u);
    // Nonblocking connect to a closed port: SO_ERROR says why.
    let nb = socket(SOCK_STREAM, 0);
    set_nonblocking(nb, true);
    let r = connect(nb, Ip([127, 0, 0, 1]), 7093);
    c.check(r == -EINPROGRESS || r == -ECONNREFUSED, "nonblocking connect to a closed port: EINPROGRESS");
    if r == -EINPROGRESS {
        let mut fds = [PollFd { fd: nb as i32, events: POLLOUT, revents: 0 }];
        poll(&mut fds, 1000);
        c.check(getsockopt_int(nb, 1, 4) == (0, ECONNREFUSED as u32), "SO_ERROR: ECONNREFUSED");
        c.check(getsockopt_int(nb, 1, 4) == (0, 0), "SO_ERROR is cleared once read");
    }
    close(nb);
    let mut sv = [0i32; 2];
    c.check(syscall5(SYS_SOCKETPAIR, 1, 1, 0, sv.as_mut_ptr() as u64, 0) == 0, "socketpair(AF_UNIX) works (stage 18)");
    close(sv[0] as i64);
    close(sv[1] as i64);
    c.check(syscall5(SYS_SOCKETPAIR, 3, 1, 0, sv.as_mut_ptr() as u64, 0) == -EAFNOSUPPORT, "socketpair(family 3): EAFNOSUPPORT");
    c.check(syscall3(SYS_SHUTDOWN, 0, 1, 0) == -88, "shutdown on a non-socket: ENOTSOCK");
}

// --- timers --------------------------------------------------------------------------

static ALRM: AtomicI64 = AtomicI64::new(0);
static TCODE: AtomicI64 = AtomicI64::new(0);
static TVAL: AtomicU64 = AtomicU64::new(0);
static TOVR: AtomicI64 = AtomicI64::new(-1);

extern "C" fn on_alarm(_sig: i32) {
    ALRM.fetch_add(1, Ordering::SeqCst);
}

extern "C" fn on_timer(_sig: i32, info: *const SigInfo, _ctx: *mut u8) {
    unsafe {
        TCODE.store((*info).code as i64, Ordering::SeqCst);
        TVAL.store(*((info as *const u8).add(24) as *const u64), Ordering::SeqCst);
        TOVR.store(*((info as *const u8).add(20) as *const i32) as i64, Ordering::SeqCst); // si_overrun
    }
    ALRM.fetch_add(1, Ordering::SeqCst);
}

fn wait_for(n: i64, ms: u64) -> bool {
    let end = now_us() + ms * 1000;
    while ALRM.load(Ordering::SeqCst) < n && now_us() < end {
        sleep_ms(5);
    }
    ALRM.load(Ordering::SeqCst) >= n
}

/// Sleep the whole `ms`: a signal cuts nanosleep short (EINTR), so go back
/// to sleep until the time is really up.
fn sleep_through(ms: u64) {
    let end = now_us() + ms * 1000;
    loop {
        let now = now_us();
        if now >= end {
            return;
        }
        nanosleep_us(end - now);
    }
}

fn itimer(value_us: u64, interval_us: u64) -> [u64; 4] {
    let new = [interval_us / 1_000_000, interval_us % 1_000_000, value_us / 1_000_000, value_us % 1_000_000];
    let mut old = [0u64; 4];
    syscall3(SYS_SETITIMER, 0, new.as_ptr() as u64, old.as_mut_ptr() as u64);
    old
}

fn timers(c: &mut Checks) {
    signal(SIGALRM, on_alarm);
    ALRM.store(0, Ordering::SeqCst);
    c.check(syscall3(SYS_ALARM, 5, 0, 0) == 0, "alarm(5): no alarm before");
    c.check(syscall3(SYS_ALARM, 0, 0, 0) == 5, "alarm(0) cancels it: 5 seconds were left");
    // One-shot setitimer.
    let t0 = now_us();
    itimer(100_000, 0);
    let mut cur = [0u64; 4];
    syscall3(SYS_GETITIMER, 0, cur.as_mut_ptr() as u64, 0);
    c.check(cur[2] == 0 && cur[3] > 0 && cur[3] <= 100_000, "getitimer: time left <= 100 ms");
    c.check(wait_for(1, 1000), "setitimer 100 ms: SIGALRM arrives");
    let dt = now_us() - t0;
    c.check(dt >= 100_000 && dt < 400_000, &format!("...after {} ms (never early)", dt / 1000));
    sleep_through(150);
    c.check(ALRM.load(Ordering::SeqCst) == 1, "one-shot: only once");
    // pause() wakes up for it.
    syscall3(SYS_ALARM, 1, 0, 0);
    let t0 = now_us();
    pause();
    c.check(ALRM.load(Ordering::SeqCst) == 2 && now_us() - t0 >= 900_000, "alarm(1) + pause: woken after a second");
    // Periodic.
    ALRM.store(0, Ordering::SeqCst);
    itimer(60_000, 60_000);
    sleep_through(500);
    let old = itimer(0, 0);
    let n = ALRM.load(Ordering::SeqCst);
    c.check((3..=9).contains(&n), &format!("periodic 60 ms timer: {} signals in 500 ms", n));
    c.check(old[0] == 0 && old[1] == 60_000, "setitimer returns the old interval");
    sleep_through(150);
    c.check(ALRM.load(Ordering::SeqCst) == n, "disarmed: no more signals");
    c.check(syscall3(SYS_SETITIMER, 1, cur.as_ptr() as u64, 0) == -EINVAL, "ITIMER_VIRTUAL: EINVAL (not supported)");
    // POSIX timers.
    sigaction_info(SIGUSR1, on_timer, 0);
    ALRM.store(0, Ordering::SeqCst);
    let mut sev = [0u64; 8];
    sev[0] = 42; // sigval
    sev[1] = SIGUSR1 as u64; // signo, notify = SIGEV_SIGNAL (0)
    let mut id = -1i32;
    let r = syscall3(SYS_TIMER_CREATE, 1, sev.as_ptr() as u64, &mut id as *mut i32 as u64);
    c.check(r == 0 && id >= 0, "timer_create(CLOCK_MONOTONIC, SIGUSR1)");
    let spec = [0u64, 0, 0, 80_000_000]; // interval 0, value 80 ms
    c.check(syscall6(SYS_TIMER_SETTIME, id as u64, 0, spec.as_ptr() as u64, 0, 0, 0) == 0, "timer_settime 80 ms");
    let mut now = [0u64; 4];
    syscall3(SYS_TIMER_GETTIME, id as u64, now.as_mut_ptr() as u64, 0);
    c.check(now[2] == 0 && now[3] > 0 && now[3] <= 80_000_000, "timer_gettime: time left <= 80 ms");
    c.check(wait_for(1, 1000), "the timer's signal arrives");
    c.check(TCODE.load(Ordering::SeqCst) == -2 && TVAL.load(Ordering::SeqCst) == 42, "si_code SI_TIMER, si_value 42");
    c.check(syscall3(SYS_TIMER_GETOVERRUN, id as u64, 0, 0) == 0, "timer_getoverrun: 0");
    // Absolute time on CLOCK_MONOTONIC, periodic.
    ALRM.store(0, Ordering::SeqCst);
    let (s, ns) = clock_gettime(1);
    let at = s * 1_000_000_000 + ns + 50_000_000;
    let spec = [0u64, 50_000_000, at / 1_000_000_000, at % 1_000_000_000];
    c.check(syscall6(SYS_TIMER_SETTIME, id as u64, 1, spec.as_ptr() as u64, 0, 0, 0) == 0, "timer_settime TIMER_ABSTIME, every 50 ms");
    c.check(wait_for(3, 1000), "...fires repeatedly");
    let zero = [0u64; 4];
    let mut old = [0u64; 4];
    syscall6(SYS_TIMER_SETTIME, id as u64, 0, zero.as_ptr() as u64, old.as_mut_ptr() as u64, 0, 0);
    c.check(old[1] == 50_000_000, "disarming returns the old interval");
    c.check(syscall3(SYS_TIMER_DELETE, id as u64, 0, 0) == 0, "timer_delete");
    c.check(syscall3(SYS_TIMER_DELETE, id as u64, 0, 0) == -EINVAL, "timer_delete again: EINVAL");
    // Overruns (stage 18 fix, found by Clarke): a 20 ms timer whose signal
    // is blocked for 0.5 s expires ~25 times but sends one signal; the
    // other ~24 add up as overruns. timer_getoverrun reports the count of
    // the last *delivered* signal: 0 while it is still pending.
    ALRM.store(0, Ordering::SeqCst);
    TOVR.store(-1, Ordering::SeqCst);
    let r = syscall3(SYS_TIMER_CREATE, 1, sev.as_ptr() as u64, &mut id as *mut i32 as u64);
    let old_mask = sigprocmask(SIG_BLOCK, sigbit(SIGUSR1)) as u64;
    let spec = [0u64, 20_000_000, 0, 20_000_000]; // every 20 ms
    syscall6(SYS_TIMER_SETTIME, id as u64, 0, spec.as_ptr() as u64, 0, 0, 0);
    sleep_through(500);
    c.check(r == 0 && syscall3(SYS_TIMER_GETOVERRUN, id as u64, 0, 0) == 0, "overrun: 0 before the first signal is delivered");
    sigprocmask(SIG_SETMASK, old_mask); // delivered now
    let first = TOVR.load(Ordering::SeqCst);
    let got = syscall3(SYS_TIMER_GETOVERRUN, id as u64, 0, 0);
    c.check(ALRM.load(Ordering::SeqCst) == 1 && (18..=30).contains(&first), &format!("blocked 0.5 s: one signal, si_overrun {} (Linux: ~24)", first));
    c.check(got == first, &format!("timer_getoverrun = the delivered signal's si_overrun ({})", got));
    c.check(wait_for(2, 1000), "unblocked: the next signal comes");
    let next = TOVR.load(Ordering::SeqCst);
    // (Not 0: timerd and signal delivery both work in ~55 ms ticks.)
    c.check((0..=10).contains(&next), &format!("...with a fresh count ({}), not the old one added", next));
    syscall3(SYS_TIMER_DELETE, id as u64, 0, 0);
    // SIGEV_NONE: nothing is sent, the time just runs down.
    sev[1] = 1u64 << 32; // notify = SIGEV_NONE
    syscall3(SYS_TIMER_CREATE, 0, sev.as_ptr() as u64, &mut id as *mut i32 as u64);
    let spec = [0u64, 0, 10, 0];
    syscall6(SYS_TIMER_SETTIME, id as u64, 0, spec.as_ptr() as u64, 0, 0, 0);
    sleep_through(50);
    syscall3(SYS_TIMER_GETTIME, id as u64, now.as_mut_ptr() as u64, 0);
    c.check(now[2] == 9 || (now[2] < 10 && now[2] >= 9), "SIGEV_NONE on CLOCK_REALTIME: the time runs down");
    syscall3(SYS_TIMER_DELETE, id as u64, 0, 0);
    c.check(syscall3(SYS_TIMER_CREATE, 2, 0, &mut id as *mut i32 as u64) == -EINVAL, "timer_create on a CPU clock: EINVAL");
    sev[1] = (99u64 << 32) | SIGUSR1 as u64;
    c.check(syscall3(SYS_TIMER_CREATE, 1, sev.as_ptr() as u64, &mut id as *mut i32 as u64) == -EINVAL, "an unknown sigev_notify: EINVAL");
    // A child's timers don't survive it.
    let pid = fork();
    if pid == 0 {
        syscall3(SYS_ALARM, 100, 0, 0);
        let mut id = 0i32;
        syscall3(SYS_TIMER_CREATE, 1, 0, &mut id as *mut i32 as u64);
        exit(0);
    }
    wait4(pid, 0).ok();
    c.check(syscall3(SYS_ALARM, 0, 0, 0) == 0, "the child's alarm isn't ours");
}

// --- ids, priority, hostname --------------------------------------------------------------

fn res(nr: u64) -> [u32; 3] {
    let mut v = [0u32; 3];
    syscall3(nr, &mut v[0] as *mut u32 as u64, &mut v[1] as *mut u32 as u64, &mut v[2] as *mut u32 as u64);
    v
}

fn in_child(f: impl FnOnce() -> i64) -> i64 {
    let pid = fork();
    if pid == 0 {
        exit(f());
    }
    match wait4(pid, 0) {
        Ok((_, s)) => wexitstatus(s) as i64,
        Err(e) => e,
    }
}

fn ids(c: &mut Checks) {
    c.check(syscall3(SYS_GETUID, 0, 0, 0) == 0 && syscall3(SYS_GETEUID, 0, 0, 0) == 0 && syscall3(SYS_GETGID, 0, 0, 0) == 0, "we start as root");
    c.check(res(SYS_GETRESUID) == [0, 0, 0], "getresuid: 0 0 0");
    // Root drops to 1000 for good.
    let r = in_child(|| {
        let mut fails = 0;
        let groups = [5u32, 6];
        fails += (syscall3(SYS_SETGROUPS, 2, groups.as_ptr() as u64, 0) != 0) as i64;
        let mut got = [0u32; 8];
        fails += (syscall3(SYS_GETGROUPS, 0, 0, 0) != 2) as i64;
        fails += (syscall3(SYS_GETGROUPS, 8, got.as_mut_ptr() as u64, 0) != 2 || got[..2] != groups) as i64;
        fails += (syscall3(SYS_GETGROUPS, 1, got.as_mut_ptr() as u64, 0) != -EINVAL) as i64;
        fails += (syscall3(SYS_SETGID, 100, 0, 0) != 0 || res(SYS_GETRESGID) != [100, 100, 100]) as i64;
        fails += (syscall3(SYS_SETUID, 1000, 0, 0) != 0 || res(SYS_GETRESUID) != [1000, 1000, 1000]) as i64;
        fails += (syscall3(SYS_SETUID, 0, 0, 0) != -EPERM) as i64;
        fails += (syscall3(SYS_SETGROUPS, 0, 0, 0) != -EPERM) as i64;
        let name = b"evil";
        fails += (syscall3(SYS_SETHOSTNAME, name.as_ptr() as u64, 4, 0) != -EPERM) as i64;
        // A file it makes is its own.
        unlink("/tmp/u1000.txt");
        write_file("/tmp/u1000.txt", b"x");
        let s = st("/tmp/u1000.txt");
        fails += (s.uid != 1000 || s.gid != 100) as i64;
        fails += (syscall3(SYS_SETPRIORITY, 0, 0, 5) != 0) as i64;
        fails += (syscall3(SYS_SETPRIORITY, 0, 0, 0) != -EACCES) as i64; // only root raises priority
        fails
    });
    c.check(r == 0, "child: setgroups/getgroups, setgid, setuid(1000) for good, then EPERM; its files are 1000:100; nice only up");
    c.check(st("/tmp/u1000.txt").uid == 1000, "the file stays 1000's");
    unlink("/tmp/u1000.txt");
    // setresuid keeps root in the saved id: it can come back.
    let r = in_child(|| {
        let mut fails = 0;
        fails += (syscall3(SYS_SETRESUID, 1000, 1000, 0) != 0) as i64;
        fails += (syscall3(SYS_GETEUID, 0, 0, 0) != 1000) as i64;
        fails += (syscall3(SYS_SETRESUID, 2000, u64::MAX, u64::MAX) != -EPERM) as i64;
        fails += (syscall3(SYS_SETUID, 0, 0, 0) != 0 || res(SYS_GETRESUID) != [1000, 0, 0]) as i64;
        // setreuid(-1, 1000): the effective id goes back to the real one, so
        // (Linux's rule) the saved id stays 0...
        fails += (syscall3(SYS_SETREUID, u32::MAX as u64, 1000, 0) != 0 || res(SYS_GETRESUID) != [1000, 1000, 0]) as i64;
        // ...while setting the real id copies the effective one into it.
        fails += (syscall3(SYS_SETUID, 0, 0, 0) != 0 || syscall3(SYS_SETREUID, 1000, 1000, 0) != 0 || res(SYS_GETRESUID) != [1000, 1000, 1000]) as i64;
        fails += (syscall3(SYS_SETUID, 0, 0, 0) != -EPERM) as i64; // no way back now
        fails
    });
    c.check(r == 0, "child: setresuid(1000,1000,0), back to euid 0 via the saved id, setreuid");
    c.check(res(SYS_GETRESUID) == [0, 0, 0], "the parent is still root");
    // Priority.
    c.check(syscall3(SYS_GETPRIORITY, 0, 0, 0) == 20, "getpriority: 20 (nice 0; the raw call returns 20 - nice)");
    c.check(syscall3(SYS_SETPRIORITY, 0, 0, 7) == 0 && syscall3(SYS_GETPRIORITY, 0, 0, 0) == 13, "setpriority nice 7 -> 13");
    c.check(in_child(|| syscall3(SYS_GETPRIORITY, 0, 0, 0)) == 13, "a child inherits it");
    c.check(syscall3(SYS_SETPRIORITY, 0, 0, (-25i64) as u64) == 0 && syscall3(SYS_GETPRIORITY, 0, 0, 0) == 40, "nice -25 is clamped to -20 (root may)");
    syscall3(SYS_SETPRIORITY, 0, 0, 0);
    c.check(syscall3(SYS_GETPRIORITY, 0, 99999, 0) == -ESRCH, "getpriority of no such process: ESRCH");
    c.check(syscall3(SYS_GETPRIORITY, 7, 0, 0) == -EINVAL, "getpriority with a bad `which`: EINVAL");
    // Host name.
    let name = b"rustbelt-test";
    c.check(syscall3(SYS_SETHOSTNAME, name.as_ptr() as u64, name.len() as u64, 0) == 0, "sethostname rustbelt-test");
    let mut u = [0u8; 6 * 65];
    c.check(uname(&mut u)[1] == "rustbelt-test", "uname shows it");
    c.check(syscall3(SYS_SETHOSTNAME, name.as_ptr() as u64, 65, 0) == -EINVAL, "a 65-byte name: EINVAL");
    let q = b"qemu";
    syscall3(SYS_SETHOSTNAME, q.as_ptr() as u64, 4, 0);
    c.check(uname(&mut u)[1] == "qemu", "back to qemu");
}

// --- misc: flock, preadv/pwritev, sendfile, sigmasks, getdents ------------------------------

static USR1: AtomicI64 = AtomicI64::new(0);
extern "C" fn on_usr1(_sig: i32) {
    USR1.fetch_add(1, Ordering::SeqCst);
}

fn misc(c: &mut Checks) {
    // flock: locks belong to the open file (not the process, not the fd).
    write_file("/tmp/fl.txt", b"x");
    let a = open("/tmp/fl.txt", O_RDWR);
    let b = open("/tmp/fl.txt", O_RDWR);
    c.check(syscall3(SYS_FLOCK, a as u64, 2, 0) == 0, "flock LOCK_EX");
    c.check(syscall3(SYS_FLOCK, b as u64, 2 | 4, 0) == -EAGAIN, "another open file: LOCK_EX|LOCK_NB is EAGAIN");
    c.check(syscall3(SYS_FLOCK, b as u64, 1 | 4, 0) == -EAGAIN, "...and LOCK_SH|LOCK_NB too");
    let a2 = dup(a);
    c.check(syscall3(SYS_FLOCK, a2 as u64, 2 | 4, 0) == 0, "a dup of the lock holder may lock again");
    c.check(syscall3(SYS_FLOCK, a as u64, 1, 0) == 0 && syscall3(SYS_FLOCK, b as u64, 1 | 4, 0) == 0, "converted to shared: others may share it");
    c.check(syscall3(SYS_FLOCK, b as u64, 8, 0) == 0 && syscall3(SYS_FLOCK, a as u64, 2, 0) == 0, "LOCK_UN, then LOCK_EX again");
    // A child blocks until the holder lets go.
    let pid = fork();
    if pid == 0 {
        // Our copies of a, a2 and b share the parent's open files: close
        // them, or the lock could never go away (like on Linux).
        close(a);
        close(a2);
        close(b);
        let fd = open("/tmp/fl.txt", O_RDWR);
        let t0 = now_us();
        let r = syscall3(SYS_FLOCK, fd as u64, 2, 0);
        exit(if r == 0 && now_us() - t0 >= 80_000 { 0 } else { 1 });
    }
    sleep_ms(150);
    close(a); // a2 still holds it
    sleep_ms(30);
    c.check(try_wait(pid) == -EAGAIN, "closing one of two fds keeps the lock");
    close(a2); // last fd: released
    let r = wait4(pid, 0);
    c.check(matches!(r, Ok((_, s)) if wexitstatus(s) == 0), "a blocked flock waits, and gets it when the last fd closes");
    c.check(syscall3(SYS_FLOCK, b as u64, 2 | 4, 0) == 0, "the child's lock went with it");
    c.check(syscall3(SYS_FLOCK, b as u64, 3, 0) == -EINVAL, "flock with a bad op: EINVAL");
    close(b);
    unlink("/tmp/fl.txt");
    // preadv / pwritev
    write_file("/tmp/pv.txt", b"0123456789");
    let fd = open("/tmp/pv.txt", O_RDWR);
    let (mut x, mut y) = ([0u8; 3], [0u8; 4]);
    let iov = [x.as_mut_ptr() as u64, 3, y.as_mut_ptr() as u64, 4];
    c.check(syscall5(SYS_PREADV, fd as u64, iov.as_ptr() as u64, 2, 2, 0) == 7 && &x == b"234" && &y == b"5678", "preadv at offset 2 into two buffers");
    c.check(lseek(fd, 0, 1) == 0, "...without moving the file offset");
    let (p, q) = (b"ab", b"cd");
    let iov = [p.as_ptr() as u64, 2, q.as_ptr() as u64, 2];
    c.check(syscall5(SYS_PWRITEV, fd as u64, iov.as_ptr() as u64, 2, 8, 0) == 4, "pwritev at 8 (past the end)");
    close(fd);
    c.check(read_file("/tmp/pv.txt") == b"01234567abcd", "the file grew to 0123456789 -> 01234567abcd");
    // sendfile
    let src = open("/tmp/pv.txt", O_RDONLY);
    let dst = open("/tmp/sf.txt", O_WRONLY | O_CREAT | O_TRUNC);
    c.check(syscall5(SYS_SENDFILE, dst as u64, src as u64, 0, 100, 0) == 12, "sendfile file -> file: 12 bytes");
    c.check(lseek(src, 0, 1) == 12, "...moving the input offset");
    let mut off = 4u64;
    let (r, w) = pipe().unwrap();
    c.check(syscall5(SYS_SENDFILE, w as u64, src as u64, &mut off as *mut u64 as u64, 3, 0) == 3 && off == 7, "sendfile at an offset into a pipe updates *offset");
    let mut buf = [0u8; 8];
    c.check(read(r, &mut buf) == 3 && &buf[..3] == b"456", "the pipe got 456");
    c.check(syscall5(SYS_SENDFILE, dst as u64, r as u64, 0, 3, 0) == -EINVAL, "sendfile from a pipe: EINVAL");
    close(r);
    close(w);
    close(src);
    close(dst);
    c.check(read_file("/tmp/sf.txt") == b"01234567abcd", "the copy matches");
    unlink("/tmp/sf.txt");
    unlink("/tmp/pv.txt");
    // ppoll / pselect6: the mask size must be 8.
    let mask = 0u64;
    let ts = [0u64, 0];
    let mut fds = [PollFd { fd: 0, events: POLLIN, revents: 0 }];
    c.check(syscall5(SYS_PPOLL, fds.as_mut_ptr() as u64, 1, ts.as_ptr() as u64, &mask as *const u64 as u64, 4) == -EINVAL, "ppoll with sigsetsize 4: EINVAL");
    let arg = [&mask as *const u64 as u64, 16];
    c.check(syscall6(SYS_PSELECT6, 0, 0, 0, 0, ts.as_ptr() as u64, arg.as_ptr() as u64) == -EINVAL, "pselect6 with sigsetsize 16: EINVAL");
    let arg = [&mask as *const u64 as u64, 8];
    c.check(syscall6(SYS_PSELECT6, 0, 0, 0, 0, ts.as_ptr() as u64, arg.as_ptr() as u64) == 0, "pselect6 with sigsetsize 8: fine");
    // ppoll's mask: a blocked, pending signal is let in for the wait only.
    signal(SIGUSR1, on_usr1);
    USR1.store(0, Ordering::SeqCst);
    let old = sigprocmask(SIG_BLOCK, sigbit(SIGUSR1)) as u64;
    kill(getpid(), SIGUSR1);
    let (r, w) = pipe().unwrap();
    let mut fds = [PollFd { fd: r as i32, events: POLLIN, revents: 0 }];
    let ts = [1u64, 0];
    let open_mask = old & !sigbit(SIGUSR1);
    let rr = syscall5(SYS_PPOLL, fds.as_mut_ptr() as u64, 1, ts.as_ptr() as u64, &open_mask as *const u64 as u64, 8);
    c.check(rr == -EINTR && USR1.load(Ordering::SeqCst) == 1, "ppoll with SIGUSR1 unblocked: EINTR, handler ran");
    c.check(sigprocmask(SIG_BLOCK, 0) as u64 & sigbit(SIGUSR1) != 0, "the old mask (SIGUSR1 blocked) is back");
    sigprocmask(SIG_SETMASK, old);
    close(r);
    close(w);
    // getdents64 while deleting (rm -r): nothing is skipped.
    for dir in ["/tmp/gd", "/mnt/disk1/gd"] {
        mkdir(dir);
        for i in 0..40 {
            write_file(&format!("{}/f{}", dir, i), b"x");
        }
        let fd = open(dir, O_RDONLY | O_DIRECTORY);
        let mut buf = [0u8; 256]; // small: many getdents calls
        let mut seen = 0;
        let mut ino_ok = true;
        loop {
            let n = getdents64(fd, &mut buf);
            if n <= 0 {
                break;
            }
            let mut names = Vec::new();
            let mut pos = 0usize;
            while pos < n as usize {
                let ino = u64::from_le_bytes(buf[pos..pos + 8].try_into().unwrap());
                let reclen = u16::from_le_bytes([buf[pos + 16], buf[pos + 17]]) as usize;
                let raw = &buf[pos + 19..pos + reclen];
                let name = core::str::from_utf8(&raw[..raw.iter().position(|&b| b == 0).unwrap_or(raw.len())]).unwrap_or("?");
                if name != "." && name != ".." {
                    names.push((alloc::string::String::from(name), ino));
                }
                pos += reclen;
            }
            for (name, ino) in names {
                let path = format!("{}/{}", dir, name);
                ino_ok &= st(&path).ino == ino;
                unlink(&path);
                seen += 1;
            }
        }
        close(fd);
        c.check(seen == 40 && rmdir(dir) == 0, &format!("{}: deleting while reading: all 40 seen, directory empty", dir));
        c.check(ino_ok, &format!("{}: d_ino matches st_ino", dir));
    }
}