JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Tech IV REAL-TIME SYSTEMS Previous Question Paper (July - 2021 - R16)
Answer any Five Questions. All Questions Carry Equal Marks.
Main
Elaborate the need of open( ) and create( ) system calls in Linux programming with an illustrative example.
Answer
In Linux programming, file management is fundamental to system operations. The open() and create() system calls are essential for establishing a connection between a process and a file, allowing the kernel to track file access via file descriptors.
The open() system call is used to gain access to an existing file or to create a new one if specified. It requires a file path and flags (such as O_RDONLY, O_WRONLY, or O_RDWR) to define the access mode. It returns a non-negative integer known as a file descriptor, which serves as a handle for subsequent I/O operations like read() or write().
The create() system call is a specialized function used to create a new file or truncate an existing one to zero length. While open() with the O_CREAT flag is now preferred in modern Linux programming, create() remains relevant for legacy compatibility and specific permission handling. It requires the file path and the file mode (permissions) as arguments.
The following example demonstrates how to use these calls to manage file access:
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
int main() {
// Using open to create a file with specific permissions
int fd = open("example.txt", O_WRONLY | O_CREAT | O_TRUNC, 0644);
if (fd < 0) {
perror("Error opening file");
return 1;
}
write(fd, "Hello, Real-Time Systems!", 25);
close(fd);
// Using creat (equivalent to open with O_CREAT | O_WRONLY | O_TRUNC)
int fd2 = creat("test.txt", 0644);
close(fd2);
return 0;
}These system calls are critical in real-time systems for managing data logs, configuration files, and inter-process communication buffers, ensuring that the kernel maintains strict control over resource allocation and file permissions.
Define a Message queue. Describe a typical usage of message queue by illustrating various operations of it.
Answer
A Message Queue is a form of asynchronous service-to-service communication used in distributed and real-time systems. It acts as an intermediate buffer that stores messages sent by a producer until they are processed by a consumer. This decoupling allows components to operate independently, ensuring that the system remains responsive even if the consumer is temporarily unavailable or overloaded.
The typical usage of a message queue involves the following core operations:
- Enqueue (Send): The producer application creates a message containing data or a task request and pushes it onto the queue. The message is stored in memory or on disk until it is successfully retrieved.
- Dequeue (Receive): The consumer application polls or is notified by the queue to retrieve the next available message. Once retrieved, the message is typically removed from the queue or marked as 'in-process'.
- Acknowledgement (Ack): After the consumer successfully processes the message, it sends an acknowledgement back to the queue. This confirms the task is complete, allowing the queue to permanently delete the message.
- Peek: This operation allows a process to inspect the message at the front of the queue without removing it, which is useful for monitoring or priority checking.
In a real-time system, message queues are essential for load leveling, where the queue absorbs spikes in incoming data, preventing the backend processing units from crashing. Furthermore, they support asynchronous processing, where a task is offloaded to the queue so the main thread can continue executing time-critical operations without waiting for the task to finish.
Explain typical operations and uses of event register object with an illustrative example.
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Discuss various services supported by TCP/IP protocol stack.
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State the need of prioritizing exceptions. Illustrate the concept of ISR with relevant diagram.
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Explain the following with respect to Vx Works:
Memory layout and memory management.
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Task states and Task priority levels.
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Discuss briefly on various commands used for disk management in UNIX.
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What are the macros used to examine the termination status returned by wait( ) and waitpid()? Explain.
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Explain how priority based scheduling work with an illustrative example in RTOS.
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Define conditional variable. State its importance.
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Give a detail description of conditional variable control block and explain various operations of it.
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