1

pipe file

제 32 강 : pipe file

2

grep | who

0 PIPSIZData

read_count

write_count

3

(system) file table

offset

inode

user per process

u-ofile01234

device

inode table

dev_tab

fd

f_offset i_size

4

(system) file table

offset

inode

user per process

u-ofile01234

device

inode table

dev_tab

fd

f_offset [0]f_offset [1]

i_size0i_size1

16 bit (64 KB) for (offset, size) is too small for regular files

5

(system) file table

offset

inode

user per process

u-ofile01234

inode table

fd

f_offset [0]f_offset [1]

i_size0i_size1

16 bit (64 KB) for (offset, size) is too small for regular files

But 16 bit is enough for pipe file (size, offset)Use 2nd word for other purpose

read_count write count

(count MOD PIPSIZ) (count MOD PIPSIZ)

Pipe file

4096 Bytes PIPSIZ

(7846, 7715)

6

7758: readp(fp)7759: int *fp;7760: {7761: register *rp, *ip;7763: rp = fp;7764: ip = rp->f_inode;7765: loop:7768: plock(ip);7772: if(rp->f_offset[1] == ip->i_size1) {7773: if(rp->f_offset[1] != 0) {7774: rp->f_offset[1] = 0;7775: ip->i_size1 = 0;7776: if(ip->i_mode&IWRITE) {7777: ip->i_mode =& ~IWRITE;7778: wakeup(ip+1);7779: }7780: }7781: 7786: prele(ip);7787: if(ip->i_count < 2)7788: return;7789: ip->i_mode =| IREAD;7790: sleep(ip+2, PPIPE);7791: goto loop;7792: }7795: u.u_offset[0] = 0;7796: u.u_offset[1] = rp->f_offset[1];7797: readi(ip);7798: rp->f_offset[1] = u.u_offset[1];7799: prele(ip);7800: }

7805: writep(fp)7806: {7807: register *rp, *ip, c;7809: rp = fp;7810: ip = rp->f_inode;7811: c = u.u_count;7812: loop:7815: plock(ip);7816: if(c == 0) {7817: prele(ip);7818: u.u_count = 0;7819: return;7820: }7825: if(ip->i_count < 2) {7826: prele(ip);7827: u.u_error = EPIPE;7828: psignal(u.u_procp, SIGPIPE);7829: return;7830: }7835: if(ip->i_size1 == PIPSIZ) {7836: ip->i_mode =| IWRITE;7837: prele(ip);7838: sleep(ip+1, PPIPE);7839: goto loop;7840: }7844: u.u_offset[0] = 0;7845: u.u_offset[1] = ip->i_size1;7846: u.u_count = min(c, PIPSIZ-u.u_offset[1]);7847: c =- u.u_count;7848: writei(ip);7849: prele(ip);7850: if(ip->i_mode&IREAD) {7851: ip->i_mode =& ~IREAD;7852: wakeup(ip+2);7853: }7854: goto loop;7855: }

7

Also alternate use of i_mode :

i_mode = IWRITE (writer is blocked) or IREAD(reader is blocked)

0 PIPSIZData

read_countf_offset[1]

write_counti_size1

i_size1: Write Counter

f_offset[1]: Read Counter

i_mode: Lock pipe file

8

7758: readp(fp)7759: int *fp;7760: {7761: register *rp, *ip;7763: rp = fp;7764: ip = rp->f_inode;7765: loop:7768: plock(ip);7772: if(rp->f_offset[1] == ip->i_size1) {7773: if(rp->f_offset[1] != 0) {7774: rp->f_offset[1] = 0;7775: ip->i_size1 = 0;7776: if(ip->i_mode&IWRITE) {7777: ip->i_mode =& ~IWRITE;7778: wakeup(ip+1);7779: }7780: }7781: 7786: prele(ip);7787: if(ip->i_count < 2)7788: return;7789: ip->i_mode =| IREAD;7790: sleep(ip+2, PPIPE);7791: goto loop;7792: }7795: u.u_offset[0] = 0;7796: u.u_offset[1] = rp->f_offset[1];7797: readi(ip);7798: rp->f_offset[1] = u.u_offset[1];7799: prele(ip);7800: }

If reader’s counter reaches writer’s counter reader must sleep

7758 (21-1)

i_size1: Write Counter

f_offset[1]: Read Counter

i_mode: Lock pipe file

After read-pipe is complete, update f_offset[1]

reset both counters to zero

9

7805: writep(fp)7806: {7807: register *rp, *ip, c;7809: rp = fp;7810: ip = rp->f_inode;7811: c = u.u_count;7812: loop:7815: plock(ip);7816: if(c == 0) {7817: prele(ip);7818: u.u_count = 0;7819: return;7820: }7825: if(ip->i_count < 2) {7826: prele(ip);7827: u.u_error = EPIPE;7828: psignal(u.u_procp, SIGPIPE);7829: return;7830: }7835: if(ip->i_size1 == PIPSIZ) {7836: ip->i_mode =| IWRITE;7837: prele(ip);7838: sleep(ip+1, PPIPE);7839: goto loop;7840: }7844: u.u_offset[0] = 0;7845: u.u_offset[1] = ip->i_size1;7846: u.u_count = min(c, PIPSIZ-u.u_offset[1]);7847: c =- u.u_count;7848: writei(ip);7849: prele(ip);7850: if(ip->i_mode&IREAD) {7851: ip->i_mode =& ~IREAD;7852: wakeup(ip+2);7853: }7854: goto loop;7855: }

i_size1: Write Counter

f_offset[1]: Read Counter

i_mode: Lock pipe file

If writer’s counterreaches max (pipe size)writer must sleep

7800 (21-1)

After write-to-pipe is complete,writei() updates the size of pipe file writei() updates i_size1

c= u.u_count /* amount of data */

PIPSIZData

( PIPSIZ – i_size1)

10

• Group of system calls (kernel service) for data exchange synchronization between different processes• Here, for pipe IPC – kernel support:

– moved data between processes– Synchronized processes (block/wakeup)

• Other IPC examples– pipe socket signal ….

• Why so many?– Varying data size, synchronization requirements – (such as frequency, speed …..)

IPC