dirRead

fn dirRead(userdata: ?*anyopaque, dr: *Dir.Reader, buffer: []Dir.Entry) Dir.Reader.Error!usize {
    const ev: *Evented = @ptrCast(@alignCast(userdata));
    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;
            var sync: CancelRegion.Sync = try .init(ev);
            defer sync.deinit(ev);
            if (dr.state == .reset) {
                ev.lseek(&sync, dr.dir.handle, 0, linux.SEEK.SET) catch |err| switch (err) {
                    error.Unseekable => return error.Unexpected,
                    else => |e| return e,
                };
                dr.state = .reading;
            }
            const n = while (true) {
                try sync.cancel_region.await(.nothing);
                const rc = linux.getdents64(dr.dir.handle, dr.buffer.ptr, @min(dr.buffer.len, std.math.maxInt(c_uint)));
                switch (linux.errno(rc)) {
                    .SUCCESS => break rc,
                    .INTR => {},
                    .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 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;
}