Need test for asynchronous I/O [closed] - c

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I am new to asynchronous I/O. I am trying to get it to work in C and Fortran codes on a Linux system. Based on what I can find out about the platform's somewhat outdated Lustre file system, the various aio routines are supported, after a fashion, but it is not clear that they can execute in true asynchronous fashion. Is there some simple code to test whether true asynchronous I/O is occurring in the execution of a code?

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What techniques can be used to reduce stack memory usage? [closed]

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I am programming for an embedded system, where resources are at premium cost.
A few techniques that I am aware of are -
Remove/Reduce unused variable/memory.
Use macros for small/inline functions.
Is there anything else that I can use for this? Also, please correct if I am wrong.
Please Note: I am not asking exclusively about low level programming.
Let's say I am bound to use some particular amount of stack memory only. My program doesn't use recursion.

Developing a custom filesystem for an operating system [closed]

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I am developing an operating system using C, Assembler and the GCC Cross Compiler. I have already implemented a working kernel that prints to the screen and allows the user to type in some simple commands. I have already looked into some file systems such as FAT32 and LFS. What other options do I have about implementing my very own filesystem?
There's always Practical File System Design with the Be File System (PDF).

How the OS ensure security? [closed]

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In the most low-level layer (0's and 1's) how the operating system ensure security? When you open an app the app instructions goes directly to the processor and the instructions are executed. How the OS interacts with the software for ensuring security?
Thnaks in advance.
In modern platforms, it's basically about execution modes on the processors. That's it: there are some instructions than can only be run in RING 0, and the kernel itself is the only process allowed to run in this mode. Take a look at these two WIKI entries.

What are configuration files? [closed]

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What are configuration files? What are their use in c programs?
Additional question: What does it mean to have an error which states "Cannot open configuration file"?
A configuration file could be any file which the program uses to persistently store options, state, or data between executions. The concept is not specific to C and is probably universal to most programming languages. It is impossible, without knowing exactly what program you are dealing with, to figure out what they are, where they would be stored, or why the program wouldn't be able to open it.

how to implement a user space multi-thread vm e.g. Erlang runtime [closed]

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How does the Erlang runtime implement a user-space multi-threaded mechanism on UNIX-like systems?
Is it implemented using something like getcontext(2) or longjump(3)?
Any related documentation would be much appreciated.
Each Erlang process is just a struct with a heap and a stack in it. So switching process is just a matter of using another struct in an queue. I think this paper describes it nicely.

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