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M7: Process management

Currently your operating system has only been able to run one process, probably sosh. In this milestone you will implement the process related system calls: process_create, process_delete, my_id, process_status and process_wait. Obviously each new process should run in its own address space. This will require you to carefully manage seL4 address spaces.

Currently process_create need only run executables that have been archived by the cpio program and placed in the boot image. All the functionality for process creation can be found in the start_first_process() in main.c. You can use this as a guide to create a clean internal SOS interface to process creation and destruction.

sosh has an exec command. This command provides a simple interface to the process_create system call. In a similar style to UNIX shells, if the third argument to exec is an '&' then it will run the process in the background. Otherwise sosh will use process_wait to wait until the child process has finished executing.

Note: the difficult part of this milestone is not process creation, it is process deletion. Now you will discover whether the data structures you have chosen have kept enough information for you to clean up a process and return the resource to the various allocators.

Adding new applications

• Create the following folder structure for your new app:

  apps/newapp
  apps/newapp/crt
  apps/newapp/crt/crt0.S
  apps/newapp/src
  apps/newapp/Makefile
  apps/newapp/Kconfig

• Copy and appropriately modify the crt0.S from sosh or tty_test.
• Use the following Makefile template to create the Makefile:

             # Targets
  TARGETS := newapp.bin
  
  # Source files required to build the target
  CFILES   := $(patsubst $(SOURCE_DIR)/%,%,$(wildcard $(SOURCE_DIR)/src/*.c))
  ASMFILES := $(patsubst $(SOURCE_DIR)/%,%,$(wildcard $(SOURCE_DIR)/crt/crt0.S))
  
  # Libraries required to build the target
  LIBS := sel4c sel4 sos
  #export DEBUG=1
  include $(SEL4_COMMON)/common.mk

• Use the following Kconfig template to create a Kconfig file:

  config APP_NEWAPP
      bool "New app"
      depends on LIB_SEL4 && LIB_SEL4_C && LIB_SOS
      select HAVE_SEL4_APPS
      help
          A new app

Build system integration

• Modify the apps/Kconfig file, adding the following line:

  source "$SEL4_APPS_PATH/newapp/Kconfig"

• Modify the apps/newapp/Kbuild file, to look like:

  apps-$(CONFIG_APP_NEWAPP) += newapp
  newapp: libsel4c libsel4 libsos

• Modify the apps/sos/Kbuild file to know about your new application and build it into the SOS cpio archive. Add the following line (where intuitively appropriate):

  sos-components-$(CONFIG_APP_NEWAPP) += newapp

• Lastly, you need to include your new application in the build process by selecting it in the configuration menu.

Design issues

As with most milestones, a lot of the design work will be working out suitable data structures to hold process information. You may also need to extend other data structures in your operating system to handle multiple processes.

You also probably want to check how the crt works, so you can make sure that when a process's main function exits it will kill itself.

Assessment

You should show sosh executing a sub-process and show that the ps command works.

You may want to add a kill command to sosh to show that process_delete works.

As always you should be able to explain the data structures and algorithms used.