#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 CHRWE (CHREAD|CHWRITE|CHEXEC) int parsemode(char *, ulong *, ulong *); voidmain(int argc, char *argv[]){	int i;	Dir dir;	ulong mode, mask;	char *p;	char err[ERRLEN]; 	if(argc < 2){		fprint(2, "usage: chmod 0777 file ... or chmod [who]op[rwxal] file ...\n");		exits("usage");	}	mode = strtol(argv[1], &p, 8);	if(*p == 0)		mask = A(CHRWE);	else if(!parsemode(argv[1], &mask, &mode)){		fprint(2, "chmod: bad mode: %s\n", argv[1]);		exits("mode");	}	for(i=2; i<argc; i++){		if(dirstat(argv[i], &dir)==-1){			errstr(err);			fprint(2, "chmod: can't stat %s: %s\n", argv[i], err);			continue;		}		dir.mode = (dir.mode & ~mask) | (mode & mask);		if(dirwstat(argv[i], &dir)==-1){			errstr(err);			fprint(2, "chmod: can't wstat %s: %s\n", argv[i], err);			continue;		}	}	exits(0);} intparsemode(char *spec, ulong *pmask, ulong *pmode){	ulong mode, mask;	int done, op;	char *s; 	s = spec;	mask = CHAPPEND | CHEXCL;	for(done=0; !done; ){		switch(*s){		case 'u':			mask |= U(CHRWE); break;		case 'g':			mask |= G(CHRWE); break;		case 'o':			mask |= O(CHRWE); break;		case 'a':			mask |= A(CHRWE); break;		case 0:			return 0;		default:			done = 1;		}		if(!done)			s++;	}	if(s == spec)		mask |= A(CHRWE);	op = *s++;	if(op != '+' && op != '-' && op != '=')		return 0;	mode = 0;	for(; *s ; s++){		switch(*s){		case 'r':			mode |= A(CHREAD); break;		case 'w':			mode |= A(CHWRITE); break;		case 'x':			mode |= A(CHEXEC); break;		case 'a':			mode |= CHAPPEND; break;		case 'l':			mode |= CHEXCL; break;		default:			return 0;		}	}	if(*s != 0)		return 0;	if(op == '+' || op == '-')		mask &= mode;	if(op == '-')		mode = ~mode;	*pmask = mask;	*pmode = mode;	return 1;}