Example code for efficiently tailing a log file

example.c

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/inotify.h>

#include <sys/stat.h>
#include <fcntl.h>

#define EVENT_SIZE  ( sizeof (struct inotify_event) )
#define EVENT_BUF_LEN     ( 1024 * ( EVENT_SIZE + 16 ) )

typedef int FD ;

int main() {
	char buffer[EVENT_BUF_LEN];

	FILE* filed = fopen("/dev/shm/typescript", "r" );
	setvbuf(filed, NULL, _IONBF, 0);

	if( !filed ) {
		printf("Openfile error\n");
		exit(-1);
	}

	char buf;
	while(read(fileno(filed), &buf, 1) > 0) {
		printf("%c",buf);
	}
	fflush(stdout);

	int fd = inotify_init();
	if ( fd < 0 ) {
		perror( "inotify_init error" );
	}

	int wd = inotify_add_watch( fd, "/dev/shm/typescript", IN_CREATE | IN_DELETE | IN_ACCESS | IN_MODIFY | IN_OPEN );

	while(1) {
		int length = read( fd, buffer, EVENT_BUF_LEN ); 
		//printf("==========\nUnblocked\n===========\n");
		if ( length < 0 ) {
			perror( "read" );
		}

		int i=0;
		while ( i < length ) {
			struct inotify_event *event = ( struct inotify_event * ) &buffer[ i ];
			if( event->len == 0) {
				while(read(fileno(filed), &buf, 1) > 0) {
					printf("%c",buf);
					fflush(stdout);
				}
			}
			i += EVENT_SIZE + event->len;
		}
	}
}