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	getns.c - 9base - revived minimalist port of Plan 9 userland to Unix
	git clone git://git.suckless.org/9base
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	---
	getns.c (1702B)
	---
	1 #include <u.h>
	2 #include <libc.h>
	3 #include <ctype.h>
	4
	5 static int
	6 isme(char *uid)
	7 {
	8 int n;
	9 char *p;
	10
	11 n = strtol(uid, &p, 10);
	12 if(*p == 0 && p > uid)
	13 return n == getuid();
	14 return strcmp(getuser(), uid) == 0;
	15 }
	16 /*
	17 * Absent other hints, it works reasonably well to use
	18 * the X11 display name as the name space identifier.
	19 * This is how sam's B has worked since the early days.
	20 * Since most programs using name spaces are also using X,
	21 * this still seems reasonable. Terminal-only sessions
	22 * can set $NAMESPACE.
	23 */
	24 static char*
	25 nsfromdisplay(void)
	26 {
	27 int fd;
	28 Dir *d;
	29 char disp, p;
	30
	31 if((disp = getenv("DISPLAY")) == nil){
	32 #ifdef __APPLE__
	33 // Might be running native GUI on OS X.
	34 disp = strdup(":0.0");
	35 if(disp == nil)
	36 return nil;
	37 #else
	38 werrstr("$DISPLAY not set");
	39 return nil;
	40 #endif
	41 }
	42
	43 /* canonicalize: xxx:0.0 => xxx:0 */
	44 p = strrchr(disp, ':');
	45 if(p){
	46 p++;
	47 while(isdigit((uchar)*p))
	48 p++;
	49 if(strcmp(p, ".0") == 0)
	50 *p = 0;
	51 }
	52
	53 /* turn /tmp/launch/:0 into _tmp_launch_:0 (OS X 10.5) */
	54 for(p=disp; *p; p++)
	55 if(*p == '/')
	56 *p = '_';
	57
	58 p = smprint("/tmp/ns.%s.%s", getuser(), disp);
	59 free(disp);
	60 if(p == nil){
	61 werrstr("out of memory");
	62 return p;
	63 }
	64 if((fd=create(p, OREAD, DMDIR\|0700)) >= 0){
	65 close(fd);
	66 return p;
	67 }
	68 if((d = dirstat(p)) == nil){
	69 free(d);
	70 werrstr("stat %s: %r", p);
	71 free(p);
	72 return nil;
	73 }
	74 if((d->mode&0777) != 0700 \|\| !isme(d->uid)){
	75 werrstr("bad name space dir %s", p);
	76 free(p);
	77 free(d);
	78 return nil;
	79 }
	80 free(d);
	81 return p;
	82 }
	83
	84 char*
	85 getns(void)
	86 {
	87 char *ns;
	88
	89 ns = getenv("NAMESPACE");
	90 if(ns == nil)
	91 ns = nsfromdisplay();
	92 if(ns == nil){
	93 werrstr("$NAMESPACE not set, %r");
	94 return nil;
	95 }
	96 return ns;
	97 }