dirReadLinux

fn dirReadLinux(userdata: ?*anyopaque, dr: *Dir.Reader, buffer: []Dir.Entry) Dir.Reader.Error!usize {
    const linux = std.os.linux;
    const t: *Threaded = @ptrCast(@alignCast(userdata));
    _ = t;
    var buffer_index: usize = 0;
    while (buffer.len - buffer_index != 0) {
        if (dr.end - dr.index == 0) {
            // Refill the buffer, unless we've already created references to
            // buffered data.
            if (buffer_index != 0) break;
            if (dr.state == .reset) {
                posixSeekTo(dr.dir.handle, 0) catch |err| switch (err) {
                    error.Unseekable => return error.Unexpected,
                    else => |e| return e,
                };
                dr.state = .reading;
            }
            const syscall: Syscall = try .start();
            const n = while (true) {
                const rc = linux.getdents64(dr.dir.handle, dr.buffer.ptr, @min(dr.buffer.len, std.math.maxInt(c_uint)));
                switch (linux.errno(rc)) {
                    .SUCCESS => {
                        syscall.finish();
                        break rc;
                    },
                    .INTR => {
                        try syscall.checkCancel();
                        continue;
                    },
                    else => |e| {
                        syscall.finish();
                        switch (e) {
                            .BADF => |err| return errnoBug(err), // Dir is invalid or was opened without iteration ability.
                            .FAULT => |err| return errnoBug(err),
                            .NOTDIR => |err| return errnoBug(err),
                            // To be consistent across platforms, iteration
                            // ends if the directory being iterated is deleted
                            // during iteration. This matches the behavior of
                            // non-Linux, non-WASI UNIX platforms.
                            .NOENT => {
                                dr.state = .finished;
                                return 0;
                            },
                            // This can occur when reading /proc/$PID/net, or
                            // if the provided buffer is too small. Neither
                            // scenario is intended to be handled by this API.
                            .INVAL => return error.Unexpected,
                            .ACCES => return error.AccessDenied, // Lacking permission to iterate this directory.
                            else => |err| return posix.unexpectedErrno(err),
                        }
                    },
                }
            };
            if (n == 0) {
                dr.state = .finished;
                return 0;
            }
            dr.index = 0;
            dr.end = n;
        }
        // Linux aligns the header by padding after the null byte of the name
        // to align the next entry. This means we can find the end of the name
        // by looking at only the 8 bytes before the next record. However since
        // file names are usually short it's better to keep the machine code
        // simpler.
        //
        // Furthermore, I observed qemu user mode to not align this struct, so
        // this code makes the conservative choice to not assume alignment.
        const linux_entry: *align(1) linux.dirent64 = @ptrCast(&dr.buffer[dr.index]);
        const next_index = dr.index + linux_entry.reclen;
        dr.index = next_index;
        const name_ptr: [*]u8 = &linux_entry.name;
        const padded_name = name_ptr[0 .. linux_entry.reclen - @offsetOf(linux.dirent64, "name")];
        const name_len = std.mem.findScalar(u8, padded_name, 0).?;
        const name = name_ptr[0..name_len :0];

        if (std.mem.eql(u8, name, ".") or std.mem.eql(u8, name, "..")) continue;

        const entry_kind: File.Kind = switch (linux_entry.type) {
            linux.DT.BLK => .block_device,
            linux.DT.CHR => .character_device,
            linux.DT.DIR => .directory,
            linux.DT.FIFO => .named_pipe,
            linux.DT.LNK => .sym_link,
            linux.DT.REG => .file,
            linux.DT.SOCK => .unix_domain_socket,
            else => .unknown,
        };
        buffer[buffer_index] = .{
            .name = name,
            .kind = entry_kind,
            .inode = linux_entry.ino,
        };
        buffer_index += 1;
    }
    return buffer_index;
}