EmbLogic » execl

Replacing a Process Image

Ankur Garg — Fri, 15 Jan 2016 10:40:34 +0000

Replacing a Process Image
=========================
- The exec function replaces current process with a new process.
- The path of new process is specified as argument to exec.
- It is defined in header :
#include
- Last argument of function should be NULL.
- It has 6 types of functions, whose prototype are :-
(i) Complete path is specified
int execl(const char * path, const char * arg0,const char * arg1,…,NULL);
(ii) If file is at one of default paths
int execlp(const char * file, const char * arg0,const char * arg1,…,NULL);
(iii) If arguments are given as an vector(array)
int execv(const char *path,char *const argv[]);
(iv) If arguments are given as an vector(array) and file is at one of default paths
int execvp(const char* file, char *const argv[]);
(v) int execle(const char *path, const char * arg0, const char * arg1,…,NULL, char *const envp[]);
(vi) int execve(const char *path, char *const argv[],char *const envp[] );

- The suffix p means to search PATH environmental variable.

- If the exec is executed successfully the statements after it will not be executed.
- It is because the current process is replaced.
- The arguments given to exec are used by main() function of new process as command line argument.
- If exec fails, it returns -1
- The open file descriptors remain open after the exec command.
- These file descriptors can be passed to exec as command and can be used by the replaced process to read/write from opened file.
- The argument is passed to exec as character.
- For this sprintf() is used.
- And for getting the file descriptors back , atoi() or integer typecasting can be used on the arguments of main().

process replacement followed by inter process comm. using file

Joon Vichitra — Mon, 22 Sep 2014 13:17:41 +0000

This is the output:

[root@localhost ipc]# ./p_comm
File Open Successfully
This is Parent with id=31340
This is child with id=31341
This is a new program which replaced the child
Write By Child:: Success
Read by Parent: Success
   Child Said:Hello Parent
Write by Parent: Success
Read By Child:: Success
   Parent said:Hi Child How are you?
Write By Child:: Success
Read by Parent: Success
   Child Said:I am Fine. U Tell?
Write by Parent: Success
Read By Child:: Success
   Parent said:We are also fine.Ok Bye
Child exit successfully and code is 0

Log File

RCS file: RCS/p_comm.c,v
Working file: p_comm.c
head: 1.4
branch:
locks: strict
access list:
symbolic names:
keyword substitution: kv
total revisions: 4; selected revisions: 4
description:
program to communicate between two process through a file
done- opening a file in rdwr mode
convert int fd into string to make compatiple with execl argument
—————————-
revision 1.4
date: 2014/09/22 12:46:24; author: root; state: Exp; lines: +13 -3
done:both read and write by parent in the same file
Note: Before executing this program make sure that “child_comm.c” file must be in the same directory
—————————-
revision 1.3
date: 2014/09/22 12:10:56; author: root; state: Exp; lines: +9 -4
1st read by the parent and then reply back to child by writing into the same file
—————————-
revision 1.2
date: 2014/09/22 11:53:56; author: root; state: Exp; lines: +10 -4
read the message written by child in a file
—————————-
revision 1.1
date: 2014/09/22 11:23:57; author: root; state: Exp;
Initial revision
=============================================================================

RCS file: RCS/child_comm.c,v
Working file: child_comm.c
head: 1.4
branch:
locks: strict
access list:
symbolic names:
keyword substitution: kv
total revisions: 4; selected revisions: 4
description:
program which will replace the child to do inter process comm through file
get fd through argv[0] and than convert into integer using atoi
—————————-
revision 1.4
date: 2014/09/22 12:48:25; author: root; state: Exp; lines: +12 -2
done:child repalace itself with this file using execl and this program then communicate with parent
note:this program is linked with p_comm.c
—————————-
revision 1.3
date: 2014/09/22 12:11:48; author: root; state: Exp; lines: +9 -2
1st write the msg for parent and then read the msg from parent using the same file
—————————-
revision 1.2
date: 2014/09/22 11:40:06; author: root; state: Exp; lines: +4 -3
got message which is to be written in file through argv[1]
write the message into file
—————————-
revision 1.1
date: 2014/09/22 11:32:27; author: root; state: Exp;
Initial revision
=============================================================================

Process replacement using execl

Joon Vichitra — Mon, 22 Sep 2014 13:09:46 +0000

RCS file: p_replace.c,v
Working file: p_replace.c
head: 1.2
branch:
locks: strict
access list:
symbolic names:
keyword substitution: kv
total revisions: 2; selected revisions: 2
description:
program to replace the child process using execl()
—————————-
revision 1.2
date: 2014/09/22 10:22:30; author: root; state: Exp; lines: +9 -1
use wait statement so that parent will wait till the child completed its execution
—————————-
revision 1.1
date: 2014/09/22 10:06:47; author: root; state: Exp;
Initial revision
=============================================================================

RCS file: child.c,v
Working file: child.c
head: 1.1
branch:
locks: strict
access list:
symbolic names:
keyword substitution: kv
total revisions: 1; selected revisions: 1
description:
sample program which replace the child when call by child through execl()
—————————-
revision 1.1
date: 2014/09/22 10:06:07; author: root; state: Exp;
Initial revision
=============================================================================