Implementation of FIFO in Linux

Implementation of FIFO in Linux

• 1.
  Implementation of FIFOin C under Linux Tushar B. Kute, http://tusharkute.com
• 2.
  FIFO • It isa named pipe, a method for passing information from one computer process to other processes using a pipe or message holding place that is given a specific name. Unlike a regular pipe, a named pipe can be used by processes that do not have to share a common process origin and the message sent to the named pipe can be read by any authorized process that knows the name of the named pipe. • A named pipe is sometimes called a "FIFO" (first in, first out) because the first data written to the pipe is the first data that is read from it.
• 3.
  Create FIFO usingin Commands • mkfifo filename • mknod filename p  Pipe
• 4.
  Example:
• 5.
  Example:
• 6.
  Accessing a FIFO •First, try reading the (empty) FIFO: cat < my_fifo • Now try writing to the FIFO. You will have to use a different terminal because the first command will now be hanging, waiting for some data to appear in the FIFO. echo “Hello World” > my_fifo
• 7.
  Accessing a FIFO
• 8.
  #include <sys/types.h> #include <sys/stat.h> int mkfifo(const char *filename, mode_t  mode); int mknod(const char *filename, mode_t mode |  S_IFIFO, (dev_t) 0); • Like themknod and mkfifo command, you can use the mknod function for making many special types of files. Using a dev_t value of 0 and ORing the file access mode with S_IFIFO is the only portable use of this function that creates a named pipe. Create a FIFO in C
• 9.
  #include<stdio.h> #include<sys/types.h> #include<sys/stat.h> int main() { int res = mkfifo("myfifo", 0766); if (res == 0)  printf("FIFO created...n"); return(0); } Create a FIFOin C
• 10.
  Output
• 11.
  Opening a FIFO •Unlike unnamed Pipe, FIFO needs to be opened for reading and writing so the file descriptors can be used alongwith it. fd = open(const char *path, O_RDONLY); fd = open(const char *path, O_WRONLY); File descriptor
• 12.
  #include <unistd.h> size_t write(int fildes, const void *buf,  size_t nbytes); • It arrangesfor the first nbytes bytes from buf to be written to the file associated with the file descriptor fildes. • It returns the number of bytes actually written. This may be less than nbytes if there has been an error in the file descriptor. If the function returns 0, it means no data was written; if it returns –1, there has been an error in the write call. The write system call
• 13.
  #include <unistd.h> size_t read(int fildes, void *buf, size_t  nbytes); • It readsup to nbytes bytes of data from the file associated with the file descriptor fildes and places them in the data area buf. • It returns the number of data bytes actually read, which may be less than the number requested. If a read call returns 0, it had nothing to read; it reached the end of the file. Again, an error on the call will cause it to return –1. The read system call
• 14.
  • Implement fullduplex communication between two independent processes using FIFO. First process accepts sentences and writes on one pipe to be read by second process and second process counts number of characters, number of words and number of lines in accepted sentences, writes this output in a text file and writes the contents of the file on second pipe to be read by first process and displays on standard output. Problem Statement
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  How to doit? FIFO-1Write sentences Read senteneces FIFO-2 Read file contents and print on screen Put into a file Analyse the Sentences Read a file at once Write the contents
• 16.
  int fd,fd1;    char * myfifo1 = "myfifo1";    char * myfifo2 = "myfifo2";    char buf[512];    mkfifo(myfifo1, 0666);    mkfifo(myfifo2, 0777);    fd = open(myfifo1, O_WRONLY);    write(fd, "Hello friends.. nWelcome..nI am Tushar B Kute", 55);          printf("Data wrote in FIFO1 by writern");    close(fd);    fd1 = open(myfifo2, O_RDONLY);    read(fd1, buf, sizeof(buf));    printf("Data received by FIFO2 by writern");    printf("%s",buf);    close(fd1); writer.c
• 17.
  pipe(file_pipe2);    /* Second pipe created */ if (pipe(file_pipe1) == 0)    /* first pipe created */ fork_result = fork();       /* Child process created */ if (fork_result == 0)  { write(file_pipe1[1], filename, strlen(filename)); printf("CHILD PROCESS: Wrote filename...n"); read(file_pipe2[0], ch, 1024); printf("CHILD PROCESS: Its contents are...n %s", ch); } else { read(file_pipe1[0], buffer, 10); printf("PARENT PROCESS: Read filename %s ...n", buffer); fp = fopen(buffer,"r"); while(!feof(fp)) { ch[count] = fgetc(fp); count++; } fclose(fp); write(file_pipe2[1], ch, strlen(ch)); printf("PARENT PROCESS: The Contents are written ...n"); reader.c
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  Output
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  tushar@tusharkute.com Thank you This presentationis created using LibreOffice Impress 4.2.7.2, can be used freely as per GNU General Public License Blogs http://digitallocha.blogspot.in http://kyamputar.blogspot.in Web Resources http://tusharkute.com