Re: Simple custom pager

Hi Stefan, Not to rush you, but any idea how long a fix will be? (Just so I can re-prioritize if need be)

Thanks, Daniel

On 07/11/2011 06:46 AM, Stefan Kalkowski wrote:

Hi Daniel,

we tried to reproduce your problem, and thereby had to recognize that in the current Fiasco.OC/Genode version there is something fundamentally broken with the rm-fault handling. We will further investigate the issue, and provide a fix as soon as possible.

Thank you for reporting the issue!

Regards Stefan

On 09.07.2011 01:45, Daniel Waddington wrote:

...

Hi, As a toy exercise I'm trying to write a very simple custom pager which simply allocates memory from RAM to handle page faults. When I try to handle the fault I get a region conflict exception. Can someone tell me why?? I think I am missing something fundamental here.

Thanks Daniel

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#include<base/printf.h> #include<base/sleep.h> #include<base/rpc_server.h> #include<cap_session/connection.h> #include<dataspace/client.h> #include<rom_session/connection.h> #include<rm_session/connection.h> #include<ram_session/connection.h> #include<root/component.h> #include<util/avl_string.h> #include<util/misc_math.h> #include<assert.h>

#define PAGE_SIZE 4096

using namespace Genode;

namespace Test {

/** * Example pager class * * @return */ class Pager : public Thread<8192> { private:

 Signal_receiver _receiver;

public:

 Signal_receiver *signal_receiver() { return&_receiver; }

 void entry();
 };

/** * Example backing store class - this one uses physical memory * */ class Physical_backing_store : public Signal_context { private: Rm_connection _rm; size_t _size;

public: // ctor Physical_backing_store(size_t size): _rm(0,_size) { _size = size; assert(_size> 0); }

 virtual ~Physical_backing_store() {
 }

 /**
  * Page fault handler.
  *
  */
 void handle_fault()
 {
   Rm_session::State state = _rm.state();

   printf("Test::Physical_backing_store:: rm session state is %s,

pf_addr=0x%lx\n", state.type == Rm_session::READ_FAULT ? "READ_FAULT" : state.type == Rm_session::WRITE_FAULT ? "WRITE_FAULT" : state.type == Rm_session::EXEC_FAULT ? "EXEC_FAULT" : "READY", state.addr);

   if (state.type == Rm_session::READY)
     return;

   try {

     Dataspace_capability _ds;
     try {
       _ds = env()->ram_session()->alloc(PAGE_SIZE);
     }
     catch(...) { PERR("Actual page allocation failed.\n"); }

     _rm.attach_at(_ds, state.addr&  ~(PAGE_SIZE - 1));

     PDBG("attached data space OK!\n");
   }
   catch (Genode::Rm_session::Region_conflict) {
     PERR("Region conflict - this should not happen\n");
   }
   catch (Genode::Rm_session::Out_of_metadata) {
     PERR("Out of meta data!\n");
   }
   catch(...) {
     PERR("Something else caused attach to fail in fault handler.\n");
   }

   return;
 }

 Rm_connection *rm() { return&_rm; }
 Dataspace_capability ds() { return _rm.dataspace(); }

     void connect_pager(Pager&  _pager) {
   /* connect pager signal receiver to the fault handler */
   _rm.fault_handler(_pager.signal_receiver()->manage(this));
 }

};

/** * Entry point for pager thread. * */ void Pager::entry() { printf("Pager thread started OK.\n");

 while (true) {
   try {
     Signal signal = _receiver.wait_for_signal();

     for (int i = 0; i<  signal.num(); i++) {
       static_cast<Physical_backing_store

*>(signal.context())->handle_fault(); } } catch (...) { PDBG("unexpected error while waiting for signal"); } } }

}

int main() { Genode::printf("Test-pager example. ;-))\n");

Test::Pager _pager;

/* start pager thread */ _pager.start();

/* create dataspace etc. */ try {

 enum { MANAGED_DS_SIZE = 64*1024*1024 };
 Test::Physical_backing_store bs(MANAGED_DS_SIZE);

 /* connect pager to fault handler */
 bs.connect_pager(_pager);

 /* attach to dataspace */
 char * addr = (char*) env()->rm_session()->attach(bs.ds());
 assert(addr);

 /* trigger read fault */
 printf("!!!Triggering fault...\n");
 printf("%c%c%c\n",addr[0],addr[1],addr[2]);

 printf("Fault handled OK.\n");

} catch(...) { PERR("Something failed ????.\n"); }

printf("test-pager completed.\n"); Genode::sleep_forever(); return 0; }

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