Re: [9fans] APE & environ

[erik quanstrom <quanstro@labs.coraid.com>]

On Tue Aug 20 15:30:28 EDT 2013, jas@corpus-callosum.com wrote:
> Temporary fix, it only rebuilds environ on successful creation
> of the new|modified variable:
>
>
>
> acme# diff -c /sys/src/ape/lib/bsd/putenv.c putenv.c
> /sys/src/ape/lib/bsd/putenv.c:2,8 - putenv.c:2,12
>   #include <unistd.h>
>   #include <fcntl.h>
>   #include <string.h>
> + #include <stdlib.h>
>
> + extern char **environ;
> + extern void _envsetup(void);
> +
>   int
>   putenv(char *s)
>   {
> /sys/src/ape/lib/bsd/putenv.c:26,31 - putenv.c:30,38
>   		if(write(f, value, n) != n)
>   			return -1;
>   		close(f);
> + 		if(environ != NULL)
> + 			free(environ);
> + 		_envsetup();
>   		return 0;
>   	} else
>   		return -1;

unfortunately this reinterprets some magic in the _envsetup.

after some discussion, and unhappiness with all possible solutions,
the least bad one seemed to be to rebuild environ.  this is way too
much code for the task, but posix shuts off easy escape routes.  note
this is completely unthreadsafe.  as per posix.

(it turns out that at least bsd does similar.)

/n/atom/patch/applied/apeputenv
/n/atom/patch/applied/envsetupmal

; pwd
/n/atom/patch/applied
; diff -c apeputenv/^(*.orig *.c)
apeputenv/putenv.c.orig:1,8 - apeputenv/putenv.c:1,56
+ #include <stdlib.h>
  #include <sys/types.h>
  #include <unistd.h>
  #include <fcntl.h>
  #include <string.h>

+ extern char **environ;
+
+ static int
+ envredo(char *s)
+ {
+ 	char *x, **p, *q, **v, *mem;
+ 	int n, nsz, nenv, esz;
+
+ 	x = strchr(s, '=');
+ 	if(x == NULL)
+ 		return -1;
+ 	nsz = x - s + 1;		/* compare the var=, not just var */
+
+ 	nenv = 1;
+ 	esz = strlen(s)+1;
+ 	for(p = environ; (q = *p) != NULL; p++){
+ 		esz += strlen(q)+1;
+ 		nenv++;
+ 	}
+
+ 	/* overestimate in the case we have changed a variable. */
+ 	v = malloc((nenv+1)*sizeof(char**) + esz);
+ 	if(v == NULL)
+ 		return -1;
+ 	mem = (char*)(v + nenv + 1);
+
+ 	nenv = 0;
+ 	for(p = environ; (q = *p) != NULL; p++){
+ 		if(strncmp(q, s, nsz) == 0)
+ 			continue;
+ 		v[nenv++] = mem;
+ 		n = strlen(q)+1;
+ 		memcpy(mem, q, n);
+ 		mem += n;
+ 	}
+ 	v[nenv++] = mem;
+ 	n = strlen(s)+1;
+ 	memcpy(mem, s, n);
+
+ 	v[nenv] = NULL;
+
+ 	free(environ);
+ 	environ = v;
+
+ 	return 0;
+ }
+
  int
  putenv(char *s)
  {
apeputenv/putenv.c.orig:26,32 - apeputenv/putenv.c:74,80
  		if(write(f, value, n) != n)
  			return -1;
  		close(f);
- 		return 0;
+ 		return envredo(s);
  	} else
  		return -1;
  }
; diff -c envsetupmal/^(*.orig *.c)
envsetupmal/_envsetup.c.orig:45,52 - envsetupmal/_envsetup.c:45,52
  	cnt = 0;
  	dfd = _OPEN("/env", 0);
  	if(dfd < 0) {
- 		static char **emptyenvp = 0;
- 		environ = emptyenvp;
+ 		environ = malloc(sizeof(char**));
+ 		*environ = NULL;
  		return;
  	}
  	ps = p = malloc(Envhunk);