dirReadLink

fn dirReadLink(
    userdata: ?*anyopaque,
    dir: Dir,
    sub_path: []const u8,
    buffer: []u8,
) Dir.ReadLinkError!usize {
    const ev: *Evented = @ptrCast(@alignCast(userdata));

    var sub_path_buffer: [PATH_MAX]u8 = undefined;
    const sub_path_posix = try pathToPosix(sub_path, &sub_path_buffer);

    var sync: CancelRegion.Sync = try .init(ev);
    defer sync.deinit(ev);
    while (true) {
        try sync.cancel_region.await(.nothing);
        const rc = linux.readlinkat(dir.handle, sub_path_posix, buffer.ptr, buffer.len);
        switch (linux.errno(rc)) {
            .SUCCESS => return @bitCast(rc),
            .INTR => {},
            .ACCES => return error.AccessDenied,
            .FAULT => |err| return errnoBug(err),
            .INVAL => return error.NotLink,
            .IO => return error.FileSystem,
            .LOOP => return error.SymLinkLoop,
            .NAMETOOLONG => return error.NameTooLong,
            .NOENT => return error.FileNotFound,
            .NOMEM => return error.SystemResources,
            .NOTDIR => return error.NotDir,
            .ILSEQ => return error.BadPathName,
            else => |err| return unexpectedErrno(err),
        }
    }
}