Re: [PATCH] Dramatically reduce # of fopen()s and fclose()s in nbase_rnd.c

On Fri, Dec 15, 2006 at 11:43:38AM -0600, Kris Katterjohn wrote:
> This simple patch dramatically reduces the number of fopen()s and
> fclose()s used when getting random numbers from nbase_rnd.c by keeping
> the rng device open.
> 
> Before:
> 
> # strace nmap -p- localhost 2>&1 | grep 'open("/dev/[au]*random"' | wc
>     512    3584   31744
> 
> After:
> 
> # strace ./nmap -p- localhost 2>&1 | grep 'open("/dev/[au]*random"' | wc
>       2      14     124

You can also compare "strace -c" output to estimate effect of the change.

> --- x/nbase/nbase_rnd.c       2006-08-29 00:42:46.000000000 -0500
> +++ y/nbase/nbase_rnd.c       2006-12-15 11:06:02.000000000 -0600
> @@ -114,14 +114,14 @@ int get_random_bytes(void *buf, int numb
>    int tmp;
>    int res;
>    struct timeval tv;
> -  FILE *fp = NULL;
> +  static FILE *fp;
>    unsigned int i;
>    short *iptr;
>    
>    if (numbytes < 0 || numbytes > 0xFFFF) return -1;
>    
>    if (bytesleft == 0) {
> -    fp = fopen("/dev/arandom", "r");
> +    if (!fp) fp = fopen("/dev/arandom", "r");
>      if (!fp) fp = fopen("/dev/urandom", "r");
>      if (!fp) fp = fopen("/dev/random", "r");
>      if (fp) {
> @@ -149,7 +149,7 @@ int get_random_bytes(void *buf, int numb
>        }
>        bytesleft = (sizeof(bytebuf) / sizeof(short)) * sizeof(short);
>        /*    ^^^^^^^^^^^^^^^not as meaningless as it looks  */
> -    } else fclose(fp);
> +    }
>    }
>    
>    if (numbytes <= bytesleft) { /* we can cover it */

I'll have to apply smth like this to update my nmap chroot patch.


-- 
ldv

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