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<span style="font-size: 10pt"><a href="/plan9/">Plan 9 from Bell Labs</a>&rsquo;s /usr/web/sources/contrib/rsc/rot13fs.c</span></p>
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Copyright © 2009 Alcatel-Lucent.<br />
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#include &lt;u.h&gt;
#include &lt;libc.h&gt;
#include &lt;auth.h&gt;
#include &lt;fcall.h&gt;
#include &lt;ctype.h&gt;

void
rot13(char *p, int n)
{
       char *ep;

       for(ep=p+n; p&lt;ep; p++)
               if(isalpha(*p))
                       if(tolower(*p) &lt;= 'm')
                               *p += 13;
                       else
                               *p -= 13;
}

int isdir[65536];
void
filter(int rd, int wr)
{
       char buf[MAXMSG+MAXFDATA], wbuf[MAXMSG+MAXFDATA];
       Fcall f;
       long n;

       while(n=sizeof buf, getS(rd, buf, &amp;f, &amp;n) == nil){
               if(f.type == Ropen)
                       isdir[f.fid] = f.qid.path&amp;CHDIR;
               if((f.type == Twrite || f.type == Rread) &amp;&amp; !isdir[f.fid])
                       rot13(f.data, f.count);
               n = convS2M(&amp;f, wbuf);
               write(wr, wbuf, n);
       }
       postnote(PNGROUP, getpid(), "spanish inquisition"); /* nobody expects this */
}

void
main(int argc, char **argv)
{
       int sfd, p[2];

       rfork(RFNOTEG);

       if(argc != 1+2){
               fprint(2, "usage: rot13fs service-in mountpoint\n");
               exits("usage");
       }

       if((sfd = open(argv[1], ORDWR)) &lt; 0)
               sysfatal("cannot open %s: %r\n", argv[1]);

       if(pipe(p) &lt; 0)
               sysfatal("pipe fails: %r\n");

       switch(rfork(RFNAMEG|RFPROC|RFFDG|RFMEM)){
       case -1:
               sysfatal("rfork fails: %r\n");
       case 0:
               close(p[0]);
               switch(fork()){
               case -1:
                       sysfatal("rfork fails: %r\n");
               case 0:
                       filter(sfd, p[1]);
                       break;
               default:
                       filter(p[1], sfd);
                       break;
               }
               _exits(0);
       default:
               close(p[1]);
               if(amount(p[0], argv[2], MREPL, "") &lt; 0)
                       sysfatal("mount fails: %r\n");
               exits(0);
       }
}
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