#include <u.h>#include <libc.h> #define U(x) (x<<6)#define G(x) (x<<3)#define O(x) (x)#define A(x) (U(x)|G(x)|O(x)) #define DMRWE (DMREAD|DMWRITE|DMEXEC) int parsemode(char *, ulong *, ulong *); voidmain(int argc, char *argv[]){	int i;	Dir *dir, ndir;	ulong mode, mask;	char *p; 	if(argc < 3){		fprint(2, "usage: chmod 0777 file ... or chmod [who]op[rwxalt] file ...\n");		exits("usage");	}	mode = strtol(argv[1], &p, 8);	if(*p == 0)		mask = A(DMRWE);	else if(!parsemode(argv[1], &mask, &mode)){		fprint(2, "chmod: bad mode: %s\n", argv[1]);		exits("mode");	}	nulldir(&ndir);	for(i=2; i<argc; i++){		dir = dirstat(argv[i]);		if(dir == nil){			fprint(2, "chmod: can't stat %s: %r\n", argv[i]);			continue;		}		ndir.mode = (dir->mode & ~mask) | (mode & mask);		free(dir);		if(dirwstat(argv[i], &ndir)==-1){			fprint(2, "chmod: can't wstat %s: %r\n", argv[i]);			continue;		}	}	exits(0);} intparsemode(char *spec, ulong *pmask, ulong *pmode){	ulong mode, mask;	int done, op;	char *s; 	s = spec;	mask = DMAPPEND | DMEXCL | DMTMP;	for(done=0; !done; ){		switch(*s){		case 'u':			mask |= U(DMRWE); break;		case 'g':			mask |= G(DMRWE); break;		case 'o':			mask |= O(DMRWE); break;		case 'a':			mask |= A(DMRWE); break;		case 0:			return 0;		default:			done = 1;		}		if(!done)			s++;	}	if(s == spec)		mask |= A(DMRWE);	op = *s++;	if(op != '+' && op != '-' && op != '=')		return 0;	mode = 0;	for(; *s ; s++){		switch(*s){		case 'r':			mode |= A(DMREAD); break;		case 'w':			mode |= A(DMWRITE); break;		case 'x':			mode |= A(DMEXEC); break;		case 'a':			mode |= DMAPPEND; break;		case 'l':			mode |= DMEXCL; break;		case 't':			mode |= DMTMP; break;		default:			return 0;		}	}	if(*s != 0)		return 0;	if(op == '+' || op == '-')		mask &= mode;	if(op == '-')		mode = ~mode;	*pmask = mask;	*pmode = mode;	return 1;}