Sigma0 is the root task (i.e. it runs in a root protection domain and it is the first task run by the hypervisor). Its initialization is controlled by command line parameters. Every parameter basically describe the operations to be performed on startup. In Sigma0 sources, every parameter is defined with PARAM_HANDLER() macro. Its first argument is the name of the parameter, the second argument is the code to be performed when the parameter is encountered in the script and the rest of arguments are lines of the help text.

After all parameters are processed, the main thread blocks and Sigma0 is controlled only through inter-process communication (IPC).

The entry point of sigma0 is the symbol start, which is defined to be the same as static method Sigma0::start() in sigma0.cc. This function is called from program.h, which defines __start symbol (an entry point defined in the linker script).

Sigma0 class iherits _free_virt members, which is a region list used to manage free virtual memory for later delegation to childs. Initially, all memory is put into this list.

Memory mapping is only possible during IPC. Therefore, to map the memory from hypervisor sigma0 calls itself through "echo portal". This is implemented in map_self() method. The actual mapping is performed by hypervisor during reply to the echo call. It cannot be done during the call, because utcb->crd of receiving thread must correspond the mapping and the caller cannot easily manipulate utcb->crd of the receiving thread.

Memory allocations (operator new) is implemented in library called service (file simplemalloc.cc). The implementation simply calls the function pointed out by memalloc pointer, whose value defaults to memalloc_mempool().

Sigma0 uses a more sofisticated memory allocator defined in sigma0_memalloc(). It allocate physical memory by consulting _free_phys region list and then maps the memory to its address space.

Memory freeing (memfree pointer) is not currently implemented.

Portal wrapper functions cannot be greped - they are defined with PT_FUNC() or PT_FUNC_NORETURN() macros.

TODO How are capability selectors allocated?

The following is the excerpt from a boot log on a 2-CPU system sorted by the capability selector (idx_*). Note that these events are not normally logged; these messages were only added for the purpose of this list. It lists the objects created in sigma0, their selectors and other parameters. Memory mapping selectors are not included in this list.

nova_create_pt(idx_pt=0x00000100, idx_ec=0x00000227, eip=0x0040c7a8, mtd=0x00000000, dstpd=0x00000020) // parent portal CPU0
nova_create_pt(idx_pt=0x00000101, idx_ec=0x0000024e, eip=0x0040c7a8, mtd=0x00000000, dstpd=0x00000020) // parent portal CPU1
nova_create_sm(idx_sm=0x00000200, initial=0, dstpd=0x00000020) // _cap_block (program.h)
nova_create_sm(idx_sm=0x00000201, initial=0, dstpd=0x00000020) // _lock_gsi
nova_create_sm(idx_sm=0x00000202, initial=0, dstpd=0x00000020) // _lock_mem
nova_create_ec(idx_ec=0x00000203, utcb=0x3fe000, esp=0x43dff4, cpunr=0, excpt_base=0x00000000, dstpd=0x00000020) // do_map portal
// Exception handling portals CPU0
nova_create_pt(idx_pt=0x00000204, idx_ec=0x00000203, eip=0x0041128a, mtd=0x00000000, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000205, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000206, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000207, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000208, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000209, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000020a, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000020b, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000020c, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000020d, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000020e, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000020f, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000210, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000211, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000212, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000213, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000214, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000215, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000216, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000217, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000218, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000219, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000021a, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000021b, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000021c, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000021d, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000021e, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000021f, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000220, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000221, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000222, idx_ec=0x00000203, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)

nova_create_pt(idx_pt=0x00000223, idx_ec=0x00000203, eip=0x00408755, mtd=0x0000000c, dstpd=0x00000020) // do_thread_startup
nova_create_ec(idx_ec=0x00000225, utcb=0x3fb000, esp=0x43cff4, cpunr=0, excpt_base=0x00000205, dstpd=0x00000020) // ec_echo
nova_create_ec(idx_ec=0x00000227, utcb=0x3f8000, esp=0x43bff4, cpunr=0, excpt_base=0x00000205, dstpd=0x00000020)
nova_create_sm(idx_sm=0x00000229, initial=0, dstpd=0x00000020)
nova_create_ec(idx_ec=0x0000022a, utcb=0x2fc000, esp=0x2faff4, cpunr=1, excpt_base=0x00000000, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000022b, idx_ec=0x0000022a, eip=0x0041128a, mtd=0x00000000, dstpd=0x00000020)

// Exception handling portals CPU1
nova_create_pt(idx_pt=0x0000022c, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000022d, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000022e, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000022f, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000230, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000231, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000232, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000233, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000234, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000235, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000236, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000237, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000238, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000239, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000023a, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000023b, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000023c, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000023d, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000023e, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000023f, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000240, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000241, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000242, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000243, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000244, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000245, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000246, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000247, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000248, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000249, idx_ec=0x0000022a, eip=0x00408d78, mtd=0x000effff, dstpd=0x00000020)

nova_create_pt(idx_pt=0x0000024a, idx_ec=0x0000022a, eip=0x00408755, mtd=0x0000000c, dstpd=0x00000020) // do_thread_startup
nova_create_ec(idx_ec=0x0000024c, utcb=0x2f8000, esp=0x2f6ff4, cpunr=1, excpt_base=0x0000022c, dstpd=0x00000020)
nova_create_ec(idx_ec=0x0000024e, utcb=0x2f4000, esp=0x2f2ff4, cpunr=1, excpt_base=0x0000022c, dstpd=0x00000020)
nova_create_sm(idx_sm=0x00000250, initial=0, dstpd=0x00000020)
nova_create_ec(idx_ec=0x00000251, utcb=0x2e9000, esp=0xbfbf6ff4, cpunr=0, excpt_base=0x00000205, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000252, idx_ec=0x00000251, eip=0x00402bfe, mtd=0x00000000, dstpd=0x00000020)
nova_create_ec(idx_ec=0x00000253, utcb=0x2e6000, esp=0xbfbf5ff4, cpunr=1, excpt_base=0x0000022c, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000254, idx_ec=0x00000253, eip=0x00402bfe, mtd=0x00000000, dstpd=0x00000020)
nova_create_ec(idx_ec=0x00000255, utcb=0x2e3000, esp=0xbfbf3ff4, cpunr=0, excpt_base=0x00000205, dstpd=0x00000020)
nova_create_sc(idx_sc=0x00000256, idx_ec=0x00000255, dstpd=0x00000020)
nova_create_ec(idx_ec=0x00000257, utcb=0x2e0000, esp=0xbfbf1ff4, cpunr=0, excpt_base=0x00000205, dstpd=0x00000020)
nova_create_sc(idx_sc=0x00000258, idx_ec=0x00000257, dstpd=0x00000020)
nova_create_ec(idx_ec=0x00000259, utcb=0x2dd000, esp=0xbfbf0ff4, cpunr=1, excpt_base=0x0000022c, dstpd=0x00000020)
nova_create_sc(idx_sc=0x0000025a, idx_ec=0x00000259, dstpd=0x00000020)
nova_create_ec(idx_ec=0x0000025c, utcb=0x2da000, esp=0xbfbeeff4, cpunr=0, excpt_base=0x00000000, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000025d, idx_ec=0x0000025c, eip=0x004045e6, mtd=0x00000000, dstpd=0x00000020)
nova_create_sm(idx_sm=0x0000025f, initial=0, dstpd=0x00000020)
nova_create_ec(idx_ec=0x00000261, utcb=0x2d7000, esp=0xbfbecff4, cpunr=1, excpt_base=0x00000000, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000262, idx_ec=0x00000261, eip=0x004045e6, mtd=0x00000000, dstpd=0x00000020)
nova_create_sm(idx_sm=0x00000264, initial=0, dstpd=0x00000020)
nova_create_ec(idx_ec=0x00000267, utcb=0x2d4000, esp=0xbfbe9ff4, cpunr=0, excpt_base=0x000fefe0, dstpd=0x00000020)
nova_create_pt(idx_pt=0x00000268, idx_ec=0x00000267, eip=0x00401b21, mtd=0x00000000, dstpd=0x00000020)
nova_create_sm(idx_sm=0x00000269, initial=0, dstpd=0x00000020)
nova_create_ec(idx_ec=0x0000026b, utcb=0x2d1000, esp=0xbfbe7ff4, cpunr=0, excpt_base=0x00000205, dstpd=0x00000020)
nova_create_ec(idx_ec=0x0000026c, utcb=0x2ce000, esp=0xbfbe6ff4, cpunr=1, excpt_base=0x000fefe4, dstpd=0x00000020)
nova_create_pt(idx_pt=0x0000026d, idx_ec=0x0000026c, eip=0x00401b21, mtd=0x00000000, dstpd=0x00000020)
nova_create_sm(idx_sm=0x0000026e, initial=0, dstpd=0x00000020)
nova_create_ec(idx_ec=0x00000270, utcb=0x2cb000, esp=0xbfbe4ff4, cpunr=1, excpt_base=0x0000022c, dstpd=0x00000020)
nova_create_sm(idx_sm=0x00000271, initial=0, dstpd=0x00000020)
nova_create_ec(idx_ec=0x00000272, utcb=0x2c8000, esp=0xbfbd4ff4, cpunr=0, excpt_base=0x00000205, dstpd=0x00000020)
nova_create_sc(idx_sc=0x00000273, idx_ec=0x00000272, dstpd=0x00000020)
nova_create_ec(idx_ec=0x00000274, utcb=0x2c5000, esp=0xbfbd2ff4, cpunr=0, excpt_base=0x00000205, dstpd=0x00000020)
nova_create_sc(idx_sc=0x00000275, idx_ec=0x00000274, dstpd=0x00000020)
nova_create_ec(idx_ec=0x00000276, utcb=0x2c2000, esp=0xbfbd0ff4, cpunr=0, excpt_base=0x00000205, dstpd=0x00000020)
nova_create_sc(idx_sc=0x00000277, idx_ec=0x00000276, dstpd=0x00000020)
nova_create_ec(idx_ec=0x00000278, utcb=0x2bf000, esp=0xbfbcfff4, cpunr=0, excpt_base=0x00000205, dstpd=0x00000020)
nova_create_sc(idx_sc=0x00000279, idx_ec=0x00000278, dstpd=0x00000020)
nova_create_sm(idx_sm=0x000100ff, initial=0, dstpd=0x00000020)
nova_create_sm(idx_sm=0x000fefd7, initial=0, dstpd=0x00000020)
nova_create_sm(idx_sm=0x000fefdc, initial=0, dstpd=0x00000020)
nova_create_pt(idx_pt=0x000fefee, idx_ec=0x0000026b, eip=0x004016dd, mtd=0x0000800f, dstpd=0x00000020)
nova_create_pt(idx_pt=0x000feff2, idx_ec=0x00000270, eip=0x004016dd, mtd=0x0000800f, dstpd=0x00000020)
nova_create_sm(idx_sm=0x000ff000, initial=0, dstpd=0x00000020)
nova_create_sm(idx_sm=0x000ff001, initial=0, dstpd=0x00000020)
nova_create_sm(idx_sm=0x000ff002, initial=0, dstpd=0x00000020)
nova_create_sm(idx_sm=0x000ff003, initial=0, dstpd=0x00000020)
nova_create_sm(idx_sm=0x000ff005, initial=0, dstpd=0x00000020)

c

The communication is currently handled by means of "devices" interconnected via various "buses". Sigma0 is also a "device". Currently, all the devices live in a single address space and therefore the bus simply pass the messages (sent by calling send_*() method) to receiving devices by calling receive() method of all devices on the bus.

Technically, the receive() methods are called by static methods inherited from StaticReceiver class template. This template generates static methods receive_static() which simply call normal member functions receive(). There might be several of these functions differentiated by the type of the message.

TimerService is a service that provides timers and time functionality to its clients. It currently runs within Sigma0, but it is planned to run in its own protection domain.

It listens on portal to perform requests from clients. The main services provided are OPEN, REQUEST_TIMER, REQUEST_TIME and CLONE. OPEN operation creates a semaphore which is shared with the client. This semaphore is signaled when a timer, set up with REQUEST_TIMER, fires.

TimerService internally uses motherboard and buses _mymb), similarly as Sigma0, but these seem not to be used for anything useful.

dot

This driver handles keyboard (and probably even mouse) IRQs, translates the scancodes somehow and sends MessageInput messages to bus_input.

The HostKeyboard 0 is special in that it allows switching consoles and reboot host and guest systems. The HostKeyboard 0 is initialized by the following SIgma0 parameter:

hostkeyb:0,0x60,1

I do not yet fully understand how console works, but it seems it might be like this:

The actual virtual consoles are implemented in HostVga. A virtual console is a set of views and the view seems to be basically a bunch of VGA and VGA memory. The emulations seems to provide both text and graphical modes. HostVga worker thread periodically (25Hz) updates the real VGA with the content of the currently selected view.

TODO How is console attached to other protection domains? What is exactly bus_console used to.

Listens for MessageInput and uses this for switching the consoles.

Starting of programs other than Sigma0 (let us call them childs) is controlled by configuration scripts (text files with .nulconfig extension). The scripts have to be loaded by the bootloader into the memory. Programs can be started either automatically by using script and script_start:<num>:1 Sigma0 parameters or manually by keyboard shortcuts (by default LWin+<num>). The number <num> refers to the num-th .nulconfig script.

The actual spawning of the program is implemented in Sigma0::_start_config(). It involves the following steps:

1. Allocation of memory and copying the executable to that memory.
2. Allocation of a console for the the new program
3. Preparation of a new Hypervisor Information Page (HIP) for the program.
4. Creation of exception handling portals (page-fault and startup).

   The portal capability selectors are allocated in the range base – base + 0x400. The base is calculated as CLIENT_PT_OFFSET + (<num>-1)*(1<<CLIENT_PT_SHIFT), i.e. for the first client the range is equal to 0x10000 - 0x10400.

5. Creation of parent protocol portals, one per CPU, staring at base + 0x100.
6. Creation of a semaphore, that is used for later identification of the client. The capability selector for this semaphore is base + 0xfd.
7. Creation of client protection domain, execution context and scheduling context (through Admission service).

   During the protection domain creation the capabilities in the range described above (base through base + 0x10400) are delegated to the client where they occupy selectors from 0x0 to 0x400. Therefore, the child knows implicitely how to contact the parent and how to idetify itself to the parent (see parent protocol).

• Although the parent protocol and the session protocol are logically different, there is some similarity between them. Namely, the parent also provides a service to clients. This service allows them to connect to other services. Because of that the CAP_PARENT_ID can be treated as the pseudonym of the child, i.e. it is used when the parent is first contacted by the child. Children uses this pseudonym to open sessions (TYPE_OPEN ) with parent. This parent-child session ID is also used as pseudonym for the other services contacted by the child.

Name of the constant (the name of the method, if it differs from the constant in anything but case and TYPE_ prefix).

Generic protocol (class GenericProtocol) is a client-side implementation of the whole protocol for talking to the service. Its method call_server() takes care of setting up everything as well as of sending the message. Typically, service specific protocols are derived from this class.

The protocol operates on a continuous range of capability selectors as shown in the table below:

The protocol is defined by the following rules:

• A portal to talk to the service (CAP_SERVER_PT) is obtained from the parent by using TYPE_GET_PORTAL message.
• A service is called by using a per-CPU portal and the client uses CAP_SERVER_SESSION capability to identify itself to the service.
• If the identity supplied by the client is not known to the callee it should return EEXISTS error.

A typical communication sequence between a client and a service (and also a parent) looks like this:

1. Client calls the service (using the operation of its choice) by using CAP_SERVER_PT selector and identifies itself to the service by CAP_SERVER_SESSION. In the beginning, the portal selector refers to the null capability and therefore the call returns NOVA_ECAP.
2. The client then calls its parent through CAP_PT_PERCPU portal and sends the TYPE_GET_PORTAL message. It identifies itself with CAP_PSEUDONYM, but because it refers to the null capability, the parent (typically Sigma0 responds with EEXIST).
3. The client calls the parent through CAP_PT_PERCPU to get the pseudonym (TYPE_OPEN) and identify itself with CAP_PARENT_ID. If the client is allowed to use the service, the parent delegates CAP_PSEUDONYM to the client.
4. Now, the client retries from step 1, but it still gets ECAP.
5. However, the it succeeds in getting the portal.
6. Then it again goes to 1 to call the service. If the service is designed to use sessions (CAP_SERVER_SESSION), EEXIST is returned (6a) and the client continues by step 7, otherwise the call is finished (6b).
7. The client sends TYPE_OPEN to the service delegates him a CAP_SERVER_SESSION.
8. Finally, the client calls the service with the original operation and a valid CAP_SERVER_SESSION and hopefully it succeeds.

… the ID field is always the session ID. Generic protocol automatically opens the session if it is required, i.e. when the call returns EEXISTS.

Ellipses represent IPC (nova_call) and arrows represent action taken based on the return of the IPC.

Server side of the protocol is implemented in class s0_ParentProtocol and …

… Services can use class ClientDataStorage to store and search for client specific data.

The following is the example how to initialize admission service and how to create a scheduling context for an ececution context.

#include "nul/service_admission.h"
...
AdmissionProtocol * service_admission;

service_admission = new AdmissionProtocol(alloc_cap(AdmissionProtocol::CAP_SERVER_PT + hip->cpu_desc_count()));
service_admission->set_name(*utcb, "My App");

unsigned ec = nova_create_ec(...);

AdmissionProtocol::sched sched(AdmissionProtocol::sched::TYPE_PERIODIC);
service_admission->alloc_sc(*myutcb(), ec, sched, service_admission->myutcb()->head.nul_cpunr, "worker thread");

The admission service is part of Sigma0 binary and is executed automatically without user intervention. You can configure the admission service by changing the content of base/apps/sigma0/cfg/admission.nulconfig. For instnace, you can remove the top parameter and add log parameter to get some logging output from the service.

NUL does not support automatic calling of constructors of static objects.