Talk:L4Re error handling

DRAFT

• interresting files ./l4sys/include/err.h, ./l4util/include/assert.h, ./l4re/include/error_helper, ./l4sys/lib/src/errtostr.c, ./cxx/lib/util/src/ipc_error_str.cc, ./cxx/lib/base/include/exceptions, ./cxx/lib/base/include/std_exc_io, ./moe/server/src/exception.cc, ./moe/server/src/exception.h, many files containing "debug", ./l4sys/include/ARCH-*/kdebug.h

• BD: JDB, the kernel debugger, could be relevant in so far that you could mention enter_kdebug().
  • usage: enter_kdebug("some message which helps others to find this call and see some state");
  • enters jdb, prints this message
  • NO jdb documentation at this time and place (BD: do you mean there's no documentation available? The basics in http://os.inf.tu-dresden.de/fiasco/doc/jdb.pdf are still valid.)

• common types which can represent error conditions: l4_cap_idx_t, Cap, l4_msgtag_t
• l4_cap_idx_t and Cap are very similar, cause Cap is a wrapper for l4_cap_idx_t
  • can be invalid
  • check l4_cap_idx_t with l4_is_invalid_cap and l4_is_valid_cap
  • check Cap with L4::Cap_base::is_valid
  • TODO where and when do we use L4::Cap_base::validate?
  • how to handle? log! also: don't support the feature which needs access to this capability... generally this means end the task
• l4_msgtag_t
  • some error conditions
  • many methods to check for more or less specific errors
  • TODO talk to someone, grep code
  • Message Tag l4_msgtag_has_error and more
  • Error handling l4_ipc_error, l4_error and more specific ones, most specific seams to be l4_ipc_error_code
  • how to handle: log! depends on specific error. often task configuration error, so end task or don't provide feature

• C++ Exceptions
  • chksys for l4_msgtag_t and long
  • chkcap for Cap<T>
  • throw some L4::Base_exception
  • has a method returning a "human readable" string! L4::Base_exception::str
  • exceptions can be printed with std::ostream
  • you can put try { } catch(e) { std::cerr << e } in your thread functions like main
  • useful usage seen in mag/server/src/main.cc

• ./l4sys/lib/src/errtostr.c
  • l4sys_errtostr(long) for L4_E* and L4_IPC_* constants
• ./cxx/lib/util/src/ipc_error_str.cc
  • TODO too funny
• TODO grep for usage