/**
 * @file cpy.c
 * @author Ron Brash ([email protected]
 * @date Sept 12, 2014
 * @brief Simple C program demonstrating posix fadvise for a file 
 * copy application
 */
#include <stdio.h>
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <error.h>
#include <string.h>
 
#include <assert.h>
 
#define BUF_SIZE 8192		// 8k ;)
 
static off_t fsize(const char *filename);
 
/**
 * fsize(const char *filename)
 * 
 * @brief Returns the filesize of a file using stat.h
 * @param filename
 * @return -1 if there is an error, zero or positive value otherwise
 */
static off_t fsize(const char *filename)
{
	struct stat st = { 0 };
 
	if (stat(filename, &st) == 0) {
 
		return st.st_size;
	}
 
	return (-1);
}
 
int main(int argc, char **argv)
{
	int inputFD = 0;
	int outputFD = 0;
	char buf[8192] = { };
	ssize_t file_size = 0;
 
	/* Open a file descriptor for the input file */
	if ((inputFD = open(argv[1], O_RDONLY)) == -1) {
		perror("Error opening input file descriptor");
		return (-1);
	}
 
	/* Determine the file_size of the input file */
	if ((file_size = fsize(argv[1])) < 0) {
		perror("Unable to determine accurate size of file");
		return (-1);
	}
 
	/* Open a file descriptor for the output file */
	if ((outputFD = open(argv[2], O_WRONLY | O_CREAT | O_TRUNC | O_APPEND, S_IRUSR | S_IWUSR)) == -1) {
		perror("Error opening output file descriptor");
		return (-1);
	}
 
	/* Lets advise the kernel that we are going to attempt a long
	 * sequential write */
	if (posix_fadvise(inputFD, 0, 0, POSIX_FADV_SEQUENTIAL) < 0) {
		perror("Unable to advise the kernel for the upcoming sequential write");
		// Continue anyways...
	}
 
	/* Read from the input file descriptor and write to the output file descriptor
	 * while keeping the 8k within the CPUs L1 cache */
	while (1) {
		file_size = read(inputFD, &buf[0], sizeof(buf));
		if (!file_size) {
			break;
		}
		assert(file_size > 0);
		assert(write(outputFD, &buf[0], file_size) == file_size);
 
	}
 
	/* Close the input file descriptor */
	if (close(inputFD) == -1) {
		perror("closing inputFD");
		return (-1);
	}
 
	/* Close the output file descriptor */
	if (close(outputFD) == -1) {
		perror("closing outputFD");
		return (-1);
	}
 
	return 0;
}