Creating new ROM sessions at runtime

[Georg Guba]

Hi Norman and Christian,

thank you both for your answers! I actually got Norman's approach working
using a slightly modified version of the demo's launchpad. With this
launchpad, all I have to do is load incoming binaries into an
Attached_ram_dataspace as Norman said.

diff --git a/repos/demo/include/launchpad/launchpad.h
b/repos/demo/include/launchpad/launchpad.h
index 9aa0ed5..2e319f8 100644
--- a/repos/demo/include/launchpad/launchpad.h
+++ b/repos/demo/include/launchpad/launchpad.h
@@ -268,7 +268,9 @@ class Launchpad
                           Genode::Allocator *alloc) { }

  Launchpad_child *start_child(const char *prg_name, unsigned long quota,
-                             Genode::Dataspace_capability config_ds);
+                             Genode::Dataspace_capability config_ds,
+                             Genode::Dataspace_capability binary_ds =
+                               Genode::Dataspace_capability());

  /**
  * Exit child and close all its sessions
diff --git a/repos/demo/src/lib/launchpad/launchpad.cc
b/repos/demo/src/lib/launchpad/launchpad.cc
index d60ad51..2fde521 100644
--- a/repos/demo/src/lib/launchpad/launchpad.cc
+++ b/repos/demo/src/lib/launchpad/launchpad.cc
@@ -186,7 +186,8 @@ void Launchpad::process_config()

 Launchpad_child *Launchpad::start_child(const char *filename,
                                         unsigned long ram_quota,
-                                        Genode::Dataspace_capability
config_ds)
+                                        Genode::Dataspace_capability
config_ds,
+                                        Genode::Dataspace_capability
binary_ds)
 {
  printf("starting %s with quota %lu\n", filename, ram_quota);

@@ -212,19 +213,27 @@ Launchpad_child *Launchpad::start_child(const char
*filename,
  /* lookup executable elf binary */
  Dataspace_capability  file_cap;
  Rom_session_capability rom_cap;
- try {
- /*
- * When creating a ROM connection for a non-existing file, the
- * constructor of 'Rom_connection' throws a 'Parent::Service_denied'
- * exception.
- */
- Rom_connection rom(filename, unique_name);
- rom.on_destruction(Rom_connection::KEEP_OPEN);
- rom_cap  = rom.cap();
- file_cap = rom.dataspace();
- } catch (...) {
- printf("Error: Could not access file \"%s\" from ROM service.\n",
filename);
- return 0;
+ if (binary_ds == Genode::Dataspace_capability())
+ {
+ /* invalid dataspace, look up in file */
+ try {
+ /*
+ * When creating a ROM connection for a non-existing file, the
+ * constructor of 'Rom_connection' throws a 'Parent::Service_denied'
+ * exception.
+ */
+ Rom_connection rom(filename, unique_name);
+ rom.on_destruction(Rom_connection::KEEP_OPEN);
+ rom_cap  = rom.cap();
+ file_cap = rom.dataspace();
+ } catch (...) {
+ printf("Error: Could not access file \"%s\" from ROM service.\n",
filename);
+ return 0;
+ }
+ }
+ else
+ {
+ file_cap = binary_ds;
  }

  /* create ram session for child with some of our own quota */

On 14 January 2016 at 18:11, Norman Feske <norman.feske at ...1...>
wrote:

> Hi Georg,
>
> > On Thu, Jan 14, 2016 at 12:29:49PM +0100, Georg Guba wrote:
> >> I'm trying to start new child components from ELF binaries received at
> >> run-time and stored in a server-local buffer. Basically, I am trying to
> >> implement a server that can receive task descriptions and matching
> binaries
> >> and then start them at run-time (disregarding security concerns for the
> >> moment).
>
> On 14.01.2016 17:06, Christian Helmuth wrote:
> > The first idea that comes to my mind is: Implement a ROM server
> > "elf_rom", which stores the retrieved ELF binaries in dataspaces
> > allocated from its RAM session.
>
> As long as your executable binary is statically linked, the problem can
> be solved in an easier way: When creating a subsystem by constructing a
> 'Child' object, you have to pass a dataspace capability for the ELF
> binary. You can simply allocate a new RAM dataspace (i.e., creating an
> 'Attached_ram_dataspace'), copy the ELF binary into the dataspace and
> pass the dataspace capability to the constructor of the 'Child'. There
> is no need to create a ROM server.
>
> However, if you want to start dynamically linked executables, the child
> component will initially start the dynamic linker, which, in turn,
> requests the executable binary along with the needed shared libraries as
> ROM sessions. Your server would need to respond to those requests by
> handing out ROM-session capabilities. As an example for this approach, I
> recommend you to look at the loader [1], which seems to be similar to
> the server you are building.
>
> [1]
> https://github.com/genodelabs/genode/tree/master/repos/os/src/server/loader
>
> Cheers
> Norman
>
> --
> Dr.-Ing. Norman Feske
> Genode Labs
>
> http://www.genode-labs.com · http://genode.org
>
> Genode Labs GmbH · Amtsgericht Dresden · HRB 28424 · Sitz Dresden
> Geschäftsführer: Dr.-Ing. Norman Feske, Christian Helmuth
>
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