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ape: get rid of fixed MUXADDR for buffered i/o

instead of trying to resize the segment (which will not work when
the kernel picks the address as it will allocate right before
the base of the topmost segment), we create the mux segment with the
maximum size needed (arround 1.4MB) for OPEN_MAX filedescriptors.

buf slots will be reused and slots get demand paged once used.

--- a/sys/src/ape/lib/ap/plan9/_buf.c

+++ b/sys/src/ape/lib/ap/plan9/_buf.c

@@ -20,10 +20,9 @@

 	int	waittime;		/* time for timer process to wait */

 	fd_set	rwant;			/* fd's that select wants to read */

 	fd_set	ewant;			/* fd's that select wants to know eof info on */

-	Muxbuf	bufs[INITBUFS];		/* can grow, via segbrk() */

+	Muxbuf	bufs[OPEN_MAX];

 } Muxseg;

-#define MUXADDR ((void*)0x6000000)

 static Muxseg *mux = 0;			/* shared memory segment */

 /* _muxsid and _killmuxsid are known in libbsd's listen.c */

@@ -50,14 +49,13 @@

 int

 _startbuf(int fd)

 {

-	long i, slot;

-	int pid, sid;

+	int i, pid, sid;

 	Fdinfo *f;

 	Muxbuf *b;

 	if(mux == 0){

 		_RFORK(RFREND);

-		mux = (Muxseg*)_SEGATTACH(0, "shared", MUXADDR, sizeof(Muxseg));

+		mux = (Muxseg*)_SEGATTACH(0, "shared", 0, sizeof(Muxseg));

 		if((long)mux == -1){

 			_syserrno();

 			return -1;

@@ -66,7 +64,7 @@

 		atexit(_killmuxsid);

 	}

-	if(fd == -1)

+	if(fd < 0)

 		return 0;

 	lock(&mux->lock);

@@ -85,17 +83,16 @@

 		errno = EIO;

 		return -1;

 	}

-

-	slot = mux->curfds++;

-	if(mux->curfds > INITBUFS) {

-		if(_SEGBRK(mux, mux->bufs+mux->curfds) < 0){

-			_syserrno();

-			unlock(&mux->lock);

-			return -1;

-		}

+	for(b = mux->bufs; b < &mux->bufs[mux->curfds]; b++)

+		if(b->fd == -1)

+			goto Found;

+	if(mux->curfds >= OPEN_MAX){

+		unlock(&mux->lock);

+		errno = ENFILE;

+		return -1;

 	}

-

-	b = &mux->bufs[slot];

+	mux->curfds++;

+Found:

 	b->n = 0;

 	b->putnext = b->data;

 	b->getnext = b->data;

-- 

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