For example, assume we are implementing :manpage:`sched_setaffinity(2)`. You must add the prototype of the function implementing it to :file:`shim_table.h`:
long shim_do_sched_setaffinity(pid_t pid, unsigned int len, unsigned long* user_mask_ptr);
Note that we use the following naming convetion: shim_do_
followed by
an actual syscall name. Additionally this function should return long
.
Now you need to add an appropriate entry in the syscalls table in
:file:`shim_table-$(ARCH).c`:
[__NR_sched_setaffinity] = (shim_fp)shim_do_sched_setaffinity
You can add the function body of shim_do_sched_setaffinity
in a new source
file or any existing source file in :file:`LibOS/shim/src/sys`.
For example, in :file:`LibOS/shim/src/sys/shim_sched.c`:
long shim_do_sched_setaffinity(pid_t pid, unsigned int len, unsigned long* user_mask_ptr) {
/* code for implementing the semantics of sched_setaffinity */
}
The concept of Gramine library OS is to keep the PAL interface as simple as possible. So, you should not add new PAL calls if the features can be fully implemented inside the library OS using the existing PAL calls. However, sometimes the OS features needed involve low-level operations inside the host OS and cannot be emulated inside the library OS. Therefore, you may have to add a |~| few new PAL calls to the existing interface.
To add a |~| new PAL call, first modify :file:`Pal/include/pal/pal.h`. Define the PAL call:
bool DkThreadSetCPUAffinity(PAL_NUM cpu_num, PAL_IDX* cpu_indexes);
The naming convention of a |~| PAL call is to start functions with the Dk
prefix, followed by a comprehensive name describing the purpose of the PAL
call.
For each directory in :file:`PAL/host/`, there is a :file:`pal.map` file. This file lists all the symbols accessible to the library OS. The new PAL call needs to be listed here in order to be used by your system call implementation.
.. todo::
(Not finished...)