If I want to add my system call vfork(copy on write) what exactly need to be edited in syscall.c? Where would I add my fragment of vfork's code. In short, how would I implement vfork in xv6?
For adding the system call in xv6's shell; amend the following files:
sysproc.c add the real implementation of your method here
syscall.h define the position of the system call vector that connect
to your implementation
user.h define the function that can be called through the shell
syscall.c external define the function that connect the shell and the
kernel, use the position defined in syscall.h to add the function to the system call vector
usys.S use the macro to define connect the call of user to the system
call function
Also you can check the following link.
Related
I have a Modbus server implemented with pymodbus. This server has a thread that update the internal registers to simulate a variable environment from the field. I need to update a file when I receive a frame containing a write function code. I tried to implement the CustomDataBlock as suggested here, but that's not exactly what I need: in this example, the code is called every time a value is changed, hence also in my "internal" updating writer function.
I want some code to be called only when my server receive a frame with writing function codes.
Any idea?
Thank you
I found the solution by myself:
inherit ModbusRtuFramer
overload processIncomingPacket function
I am trying to change the UVM verbosity of the simulation after satisfying certain conditions. Verbosity options of different components are passing through the command line as +uvm_set_verbosity. Once the conditions are satisfied, then the simulations should run with the the command line +uvm_set_verbosity option. Till then simulation runs with low verbosity for all components.
Looking through the UVM library code, it appears that there is a function called m_set_cl_msg_args(). This function calls three other functions that appear to consume the command line arguments like: +uvm_set_verbosity, +uvm_set_action, +uvm_set_severity.
So what I did was get the uvm_root instance from the uvm_coreservice singleton, and then use the get_children() function from uvm_component class to recursively get a queue of all of the uvm_components in the simulation. Then call the m_set_cl_msg_args() function on all of the components.
My code looks like:
begin
uvm_root r;
uvm_coreservice_t cs_t;
uvm_component array_uvm[$];
cs_t = uvm_coreservice_t::get();
r = cs_t.get_root();
r.get_children(array_uvm);
foreach(array_uvm[i])
array_uvm[i].m_set_cl_msg_args();
end
Even though this code compiles properly, But this is not changing verbosity. Any idea ?
Moreover I am able to print all the components in array_uvm. So I am guessing
array_uvm[i].m_set_cl_msg_args();
this as a wrong call.
Anyone have any other suggestion to change verbosity during run time.
You should never use functions in the UVM that are not documented in the language reference manual. They can (and do) change in any revision. I'm guessing +uvm_set_verbosity only works at time 0 by default.
There is already a function to do what you want
umm_top.set_report_verbosity_level_hier()
I suggest using +UVM_VERBOSITY=UVM_LOW to start your test, and then define your own switch for activating the conditional setting.
If you want a specific component, use component_h.set_report_verbosity_level() (add the _hier to set all its children)
You can use the UVM's command line processor get_arg_values() method to specify the name of the component(s) you want to set, and then use umm_top.find() to get a handle to the component.
I am writing a program that creates Simulink Models using commands in MATLAB. Currently, any subsystem that is added will be cleared immediately, then repopulated with the blocks we want in it. My question is how could I add a the While Iterator Block back into the subsystem after it has been cleared?
Sample code:
new_system('test_while_loop')
add_block('simulink/Ports & Subsystems/While Iterator Subsystem', 'test_while_loop/Subsystem_loop')
Simuink.SubSystem.deleteContents('test_while_loop/Subsystem_loop')
add_block('simulink/Ports & Subsystems/While Iterator', 'test_while_looop/Subsystem_loop/While Iterator')
This comes back with the error There is no block named 'simulink/Ports & Subsystems/While Iterator, even though the documentation for Simulink says that this block is contained within the Ports & Subsystems library. What do I need to change to be able to add this block?
For built-in blocks you should use block type to add the block to your system. To identify the block type use
get_param(gcb, 'BlockType')
For the while iterator block this will return 'WhileIterator'. You can add this block to your system using
add_block('built-in/WhileIterator','test_while_looop/Subsystem_loop/While Iterator')
See documentation for add_block at https://www.mathworks.com/help/simulink/slref/add_block.html.
I am going through the book by Galvin on OS . There is a section at the end of chapter 2 where the author writes about "adding a system call " to the kernel.
He describes how using asmlinkage we can create a file containing a function and make it qualify as a system call . But in the next part about how to call the system call he writes the following :
" Unfortunately, these are low-level operations that cannot be performed using C language statements and instead require assembly instructions. Fortunately, Linux provides macros for instantiating wrapper functions that contain the appropriate assembly instructions. For instance, the following C program uses the _syscallO() macro to invoke the newly defined system call:
Basically , I want to understand how syscall() function generally works . Now , what I understand by Macros is a system for text substitution .
(Please correct me If I am wrong)
How does a macro call an assembly language instruction ?
Is it so that syscallO() when compiled is translated into the address(op code) of the instruction to execute a trap ?(But this somehow doesn't fit with concept or definition of macros that I have )
What exactly are the wrapper functions that are contained inside and are they also written in assembly language ?
Suppose , I want to create a function of my own which performs the system call then what are the things that I need to do . Do , I need to compile it to generate the machine code for performing Trap instructions ?
Man, you have to pay $156 dollars to by the thing, then you actually have to read it. You could probably get an VMS Internals and Data Structures book for under $30.
That said, let me try to translate that gibberish into English.
System calls do not use the same kind of linkage (i.e. method of passing parameters and calling functions) that other functions use.
Rather than executing a call instruction of some kind, to execute a system service, you trigger an exception (which in Intel is bizarrely called an interrupt).
The CPU expects the operating system to create a DISPATCH TABLE and store its location and size in a special hardware register(s). The dispatch table is an array of pointers to handlers for exceptions and interrupts.
Exceptions and interrupts have numbers so, when exception or interrupt number #1 occurs, the CPU invokes the 2d exception handler (not #0, but #1) in the dispatch table in kernel mode.
What exactly are the wrapper functions that are contained inside and are they also written in assembly language ?
The operating system devotes usually one (but sometimes more) exceptions to system services. You need to do some thing like this in assembly language to invoke a system service:
INT $80 ; Explicitly trigger exception 80h
Because you have to execute a specific instruction, this has to be one in assembly language. Maybe your C compiler can do assembly language in line to call system service like that. But even if it could, it would be a royal PITA to have to do it each time you wanted to call a system service.
Plus I have not filled in all the details here (only the actual call to the system service). Normally, when you call functions in C (or whatever), the arguments are pushed on the program stack. Because the stack usually changes when you enter kernel mode, arguments to system calls need to be stored in registers.
PLUS you need to identify what system service you want to execute. Usually, system services have numbers. The number of the system service is loaded into the first register (e.g., R0 or AX).
The full process when you need to invoke a system service is:
Save the registers you are going to overwrite on the stack.
Load the arguments you want to pass to the system service into hardware registers.
Load the number of the system service into the lowest register.
Trigger the exception to enter kernel mode.
Unload the arguments returned by the system service from registers
Possibly do some error checking
Restore the registers you saved before.
Instead of doing this each time you call a system service, operating systems provide wrapper functions for high level languages to use. You call the wrapper as you would normally call a function. The wrapper (in assembly language) does the steps above for you.
Because these wrappers are pretty much the same (usually the only difference is the result of different numbers of arguments), wrappers can be created using macros. Some assemblers have powerful macro facilities that allow a single macro to define all wrappers, even with different numbers of arguments.
Linux provides multiple _syscall C macros that create wrappers. There is one for each number of arguments. Note that these macros are just for operating system developers. Once the wrapper is there, everyone can use it.
How does a macro call an assembly language instruction ?
These _syscall macros have to generate in line assembly code.
Finally, note that these wrappers do not define the actual system service. That has to be set up in the dispatch table and the system service exception handler.
I have a virtual subsystem with a bunch of parameters. I would like to use those parameters to calculate other properties of the block. This needs to be done before the simulation starts, but after the block has been initialized.
I created a script that would do the calculations, and tried to get it to run from the StartFcn block callback. But the script cannot access the parameters (which are input by the user through the mask) in the callback. I'm guessing this is because those parameters aren't available in the Matlab workspace, only within the block.
Is there any way to access those parameters through StartFcn? Failing that, is there another way, instead of the StartFcn, through which I can perform some calculations BEFORE simulation starts?
To clarify, I cannot use the Initialization tab in the block's mask because the script requires data from other blocks too (which are available in the workspace at the start of the simulation).
Your guess is correct, block callbacks are evaluated in the base workspace, but mask parameters are part of the mask's private workspace. To access them use get_param and gcb within your callback function.
value = get_param(gcb, 'my_param_name');