pipe를 이해하기 전, 일단 gdb를 사용하는 방법을 알아야 했다. pipe가 서로 다른 프로세스를 연결하는 수단이라, gdb 기본 설정으로는 pipe로 어떤 내용을 확인하기 어려웠다. 아래 코드를 디버그 하기로 했다.
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <string.h>
#define MAXLINE 100
void client(int, int), server(int, int);
void server(int readfd, int writefd){
char buff[MAXLINE];
int n;
n = read(readfd, buff, MAXLINE);
printf("서버가 읽은 data는 %s\n",buff);
}
void client(int readfd, int writefd)
{
size_t len;
ssize_t n;
char buff[MAXLINE];
/* 4read pathname */
fgets(buff, MAXLINE, stdin);
len = strlen(buff); /* fgets() guarantees null byte at end */
if (buff[len-1] == '\n')
len--; /* delete newline from fgets() */
/* 4write pathname to IPC channel */
write(writefd, buff, len);
/* 4read from IPC, write to standard output */
while ( (n = read(readfd, buff, MAXLINE)) > 0)
write(STDOUT_FILENO, buff, n);
}
int main(int argc, char **argv)
{
int pipe1[2], pipe2[2];
pid_t childpid, childpid2;
pid_t zombieFlag;
if( pipe(pipe1) < 0)
exit(1);
if (pipe(pipe2) < 0)
exit(1);
printf("made pipe1, pipe2\n");
//child process pipe 닫음.
if( (childpid = fork()) == 0) { //난 자식..
close(pipe1[1]);
close(pipe2[0]);
childpid2 = getpid();
printf("자식 process는 %d\n",childpid2);
server(pipe1[0], pipe2[1]);
// pipe1 ----> server, server process 입력은 pipe1 출력.
// pipe2 <---- server, server process 출력은 pipi2 입력.
exit(0);
}
// 난 부모.
close(pipe1[0]);
close(pipe2[1]);
client(pipe2[0], pipe1[1]);
zombieFlag = waitpid(childpid, NULL, 0);
printf("종료된 자식 process는 %d\n",zombieFlag);
//sleep(1);
exit(0);
}
이 내용을 gdb로 확인했다. gdb를 그냥 실행하면 detach-on-fork 옵션을 on으로 갖는다. child process로 분기하면 기존 프로세스를 끝까지 실행하는 옵션인 듯 하다. parent 프로세스를 정지시키고, inferior로 child 프로세스로 이동하여 나머지를 실행하고 싶었다. 그러나 detach-on-fork off 에서는 프로세스가 끝나 inferior로 이동해도 실행할 수 없다. detatch-on-fork off로 기존 프로세스를 멈추고 inferior로 다른 프로세스로 옮겨 확인했다.
pi@raspberrypi:~/Project/cCode/IPC $ gdb ./a.out
GNU gdb (Raspbian 8.2.1-2) 8.2.1
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "arm-linux-gnueabihf".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./a.out...done.
(gdb) show detach-on-fork
Whether gdb will detach the child of a fork is on.
(gdb) set detach-on-fork off
(gdb) show follow-fork-mode
Debugger response to a program call of fork or vfork is "parent".
(gdb) l
31 write(writefd, buff, len);
32
33 /* 4read from IPC, write to standard output */
34 while ( (n = read(readfd, buff, MAXLINE)) > 0)
35 write(STDOUT_FILENO, buff, n);
36 }
37
38
39 int main(int argc, char **argv)
40 {
(gdb) l 2
1 #include <stdlib.h>
2 #include <stdio.h>
3 #include <unistd.h>
4 #include <sys/types.h>
5 #include <sys/wait.h>
6 #include <string.h>
7 #define MAXLINE 100
8
9 void client(int, int), server(int, int);
10
(gdb) l
11 void server(int readfd, int writefd){
12 char buff[MAXLINE];
13 int n;
14 n = read(readfd, buff, MAXLINE);
15 printf("서버가 읽은 data는 %s\n",buff);
16 }
17
18 void client(int readfd, int writefd)
19 {
20 size_t len;
(gdb) b 14
Breakpoint 1 at 0x10658: file pipe.c, line 14.
(gdb) l
21 ssize_t n;
22 char buff[MAXLINE];
23
24 /* 4read pathname */
25 fgets(buff, MAXLINE, stdin);
26 len = strlen(buff); /* fgets() guarantees null byte at end */
27 if (buff[len-1] == '\n')
28 len--; /* delete newline from fgets() */
29
30 /* 4write pathname to IPC channel */
(gdb) b 25
Breakpoint 2 at 0x106a4: file pipe.c, line 25.
(gdb) r
Starting program: /home/pi/Project/cCode/IPC/a.out
made pipe1, pipe2
[New inferior 2 (process 2918)]
Reading symbols from /home/pi/Project/cCode/IPC/a.out...done.
Reading symbols from /usr/lib/debug/.build-id/ef/dd27c16f5283e5c53dcbd1bbc3ef136e312d1b.debug...done.
Reading symbols from /usr/lib/debug/.build-id/fb/85e699c11db06c7b24f74de2cdada3146442a8.debug...done.
Thread 1.1 "a.out" hit Breakpoint 2, client (readfd=5, writefd=4)
at pipe.c:25
25 fgets(buff, MAXLINE, stdin);
(gdb) n
this is a test.
26 len = strlen(buff); /* fgets() guarantees null byte at end */
(gdb) display buff
1: buff = "this is a test.\n\000\000\000\000\001\000\000\000\000\360\377\266$\364\377\276T\332\375\266 \230\377\266\001\000\000\000\001\000\000\000\000\000\000\000\370\234\377\266\354j\346\266f\v\000\000\000\000\000\000p\b\001\000T\005\001", '\000' <repeats 13 times>, "D;\376\266\003\000\000\000\000\000\000"
(gdb) n
27 if (buff[len-1] == '\n')
1: buff = "this is a test.\n\000\000\000\000\001\000\000\000\000\360\377\266$\364\377\276T\332\375\266 \230\377\266\001\000\000\000\001\000\000\000\000\000\000\000\370\234\377\266\354j\346\266f\v\000\000\000\000\000\000p\b\001\000T\005\001", '\000' <repeats 13 times>, "D;\376\266\003\000\000\000\000\000\000"
(gdb) n
28 len--; /* delete newline from fgets() */
1: buff = "this is a test.\n\000\000\000\000\001\000\000\000\000\360\377\266$\364\377\276T\332\375\266 \230\377\266\001\000\000\000\001\000\000\000\000\000\000\000\370\234\377\266\354j\346\266f\v\000\000\000\000\000\000p\b\001\000T\005\001", '\000' <repeats 13 times>, "D;\376\266\003\000\000\000\000\000\000"
(gdb) n
31 write(writefd, buff, len);
1: buff = "this is a test.\n\000\000\000\000\001\000\000\000\000\360\377\266$\364\377\276T\332\375\266 \230\377\266\001\000\000\000\001\000\000\000\000\000\000\000\370\234\377\266\354j\346\266f\v\000\000\000\000\000\000p\b\001\000T\005\001", '\000' <repeats 13 times>, "D;\376\266\003\000\000\000\000\000\000"
(gdb) n
34 while ( (n = read(readfd, buff, MAXLINE)) > 0)
1: buff = "this is a test.\n\000\000\000\000\001\000\000\000\000\360\377\266$\364\377\276T\332\375\266 \230\377\266\001\000\000\000\001\000\000\000\000\000\000\000\370\234\377\266\354j\346\266f\v\000\000\000\000\000\000p\b\001\000T\005\001", '\000' <repeats 13 times>, "D;\376\266\003\000\000\000\000\000\000"
(gdb) n
^Z
Thread 1.1 "a.out" received signal SIGTSTP, Stopped (user).
0xb6f2187c in __GI___libc_read (fd=5, buf=0xbefff384, nbytes=100)
at ../sysdeps/unix/sysv/linux/read.c:26
26 ../sysdeps/unix/sysv/linux/read.c: 그런 파일이나 디렉터리가 없습니다.
(gdb) info inferiors
Num Description Executable
* 1 process 2915 /home/pi/Project/cCode/IPC/a.out
2 process 2918 /home/pi/Project/cCode/IPC/a.out
(gdb) inferior 2
[Switching to inferior 2 [process 2918] (/home/pi/Project/cCode/IPC/a.out)]
[Switching to thread 2.1 (process 2918)]
#0 arch_fork (ctid=0xb6ff9cf8) at ../sysdeps/unix/sysv/linux/arch-fork.h:40
40 ../sysdeps/unix/sysv/linux/arch-fork.h: 그런 파일이나 디렉터리가 없습니다.
(gdb) c
Continuing.
Thread 2.1 "a.out" received signal SIGTSTP, Stopped (user).
arch_fork (ctid=0xb6ff9cf8) at ../sysdeps/unix/sysv/linux/arch-fork.h:40
40 in ../sysdeps/unix/sysv/linux/arch-fork.h
(gdb) c
Continuing.
Thread 2.1 "a.out" received signal SIGTSTP, Stopped (user).
arch_fork (ctid=0xb6ff9cf8) at ../sysdeps/unix/sysv/linux/arch-fork.h:40
40 in ../sysdeps/unix/sysv/linux/arch-fork.h
(gdb)
Continuing.
자식 process는 2918
Thread 2.1 "a.out" hit Breakpoint 1, server (readfd=3, writefd=6)
at pipe.c:14
14 n = read(readfd, buff, MAXLINE);
(gdb) display buff
2: buff = "x\371\377\266,\003\001\000P\241\377\266\000\000\000\000\001\000\000\000\000\360\377\266$\364\377\276T\332\375\266\062\071\061\070\000:\215\371\001\000\000\000h\351\377\266p\b\001\000T\005\001", '\000' <repeats 14 times>, "\360\377\266$\364\377\276pD\352\266\354\363\377\276\000:\215\371\000\000\000\000\364\a\001\000\024\t\001"
(gdb) n
15 printf("서버가 읽은 data는 %s\n",buff);
2: buff = "this is a test.\000\001\000\000\000\000\360\377\266$\364\377\276T\332\375\266\062\071\061\070\000:\215\371\001\000\000\000h\351\377\266p\b\001\000T\005\001", '\000' <repeats 14 times>, "\360\377\266$\364\377\276pD\352\266\354\363\377\276\000:\215\371\000\000\000\000\364\a\001\000\024\t\001"
(gdb) n
서버가 읽은 data는 this is a test.
16 }
2: buff = "this is a test.\000\001\000\000\000\000\360\377\266$\364\377\276T\332\375\266\062\071\061\070\000:\215\371\001\000\000\000h\351\377\266p\b\001\000T\005\001", '\000' <repeats 14 times>, "\360\377\266$\364\377\276pD\352\266\354\363\377\276\000:\215\371\000\000\000\000\364\a\001\000\024\t\001"
(gdb) n
main (argc=1, argv=0xbefff574) at pipe.c:63
63 exit(0);
(gdb) c
Continuing.
[Inferior 2 (process 2918) exited normally]
(gdb) c
Continuing.
Thread 1 "a.out" received signal SIGTSTP, Stopped (user).
0xb6f2187c in __GI___libc_read (fd=5, buf=0xbefff384, nbytes=100)
at ../sysdeps/unix/sysv/linux/read.c:26
26 ../sysdeps/unix/sysv/linux/read.c: 그런 파일이나 디렉터리가 없습니다.
(gdb) c
Continuing.
종료된 자식 process는 2918
[Inferior 1 (process 2915) exited normally]
다음은 수정된 코드이다.
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <string.h>
#include <errno.h>
#define MAXLINE 100
void client(int, int), server(int, int);
void server(int readfd, int writefd){
/*
char buff[MAXLINE];
int n;
n = read(readfd, buff, MAXLINE);
printf("서버가 읽은 data는 %s\n",buff);
// 샘플 테스트용..
*/
int fd;
ssize_t n;
char buff[MAXLINE+1];
/* 4read pathname from IPC channel */
if ( (n = read(readfd, buff, MAXLINE)) == 0)
perror("end-of-file while reading pathname");
buff[n] = '\0'; /* null terminate pathname */
if ( (fd = open(buff, O_RDONLY)) < 0) {
/* 4error: must tell client */
snprintf(buff + n, sizeof(buff) - n, ": can't open, %s\n",
strerror(errno));
n = strlen(buff);
write(writefd, buff, n);
} else {
/* 4open succeeded: copy file to IPC channel */
while ( (n = read(fd, buff, MAXLINE)) > 0)
write(writefd, buff, n);
close(fd);
}
}
void client(int readfd, int writefd)
{
size_t len;
ssize_t n;
char buff[MAXLINE];
/* 4read pathname */
fgets(buff, MAXLINE, stdin);
len = strlen(buff); /* fgets() guarantees null byte at end */
if (buff[len-1] == '\n')
len--; /* delete newline from fgets() */
/* 4write pathname to IPC channel */
write(writefd, buff, len);
/* 4read from IPC, write to standard output */
while ( (n = read(readfd, buff, MAXLINE)) > 0)
write(STDOUT_FILENO, buff, n);
}
int main(int argc, char **argv)
{
int pipe1[2], pipe2[2];
pid_t childpid, childpid2;
pid_t zombieFlag;
if( pipe(pipe1) < 0)
exit(1);
if (pipe(pipe2) < 0)
exit(1);
printf("made pipe1, pipe2\n");
//child process pipe 닫음.
if( (childpid = fork()) == 0) { //난 자식..
close(pipe1[1]);
close(pipe2[0]);
childpid2 = getpid();
printf("자식 process는 %d\n",childpid2);
server(pipe1[0], pipe2[1]);
// pipe1 ----> server, server process 입력은 pipe1 출력.
// pipe2 <---- server, server process 출력은 pipi2 입력.
exit(0);
}
// 난 부모.
close(pipe1[0]);
close(pipe2[1]);
client(pipe2[0], pipe1[1]);
zombieFlag = waitpid(childpid, NULL, 0);
printf("종료된 자식 process는 %d\n",zombieFlag);
//sleep(1);
exit(0);
}
pi@raspberrypi:~/Project/cCode/IPC $ cat test.txt 안녕하세요. hello. pi@raspberrypi:~/Project/cCode/IPC $ ./a.out made pipe1, pipe2 자식 process는 4890 this is a test. this is a test.: can't open, No such file or directory 종료된 자식 process는 4890 pi@raspberrypi:~/Project/cCode/IPC $ ./a.out made pipe1, pipe2 자식 process는 4893 ./test ./test: can't open, No such file or directory 종료된 자식 process는 4893 pi@raspberrypi:~/Project/cCode/IPC $ ./a.out made pipe1, pipe2 자식 process는 4895 ./test.txt 안녕하세요. hello. 종료된 자식 process는 4895
잘 실행된다. pipe를 만들고 파이프 양 끝에 입력, 출력으로 생각했는데, 이러면 헷갈린다. 프로세스 기준으로 입력, 출력을 생각하고 파이프로 연결한다 생각하면 쉽다.
하… 가벼운 마음으로 들어왔는데 IPC를 책 한 권에 걸쳐 설명하네.