#include "sys.h"
#include "buf.h"
#include "sup.h"
#include "proc.h"

       /*
	* Allocate a disk block from the device freelist.
	* See Unix Programmer's Manual, section V, File System
	* for a description of the algorithm.
	*/
balloc(dev)
	int  dev;
	{
	fast struct buf *sb;
	static struct buf *fb;
	fast struct sup *sup;
	fast int bn;

	sb  = getsb(dev);
	sup = sb->data;
	if (sup->flock)		/* mounted read-only */
		{
		u.error = EROFS;
		return (0);
		}
	if (sup->nfree <= 0
	||
	(bn = sup->free[--sup->nfree]) == 0
	||
	bcheck(bn, sup, dev) == NO)
		goto full;

	if (sup->nfree == 0)
		{
		if ((fb = bread(bn, dev)) == NULL)
			goto bad;
		copy(fb->data, &sup->nfree, 202);	/* PORT */
		}
	else
		{
		fb = bget(bn, dev);
		}

	zero(fb->data, 512);
	bdwrite(fb);
	bdwrite(sb);
	return (bn);
    full:
	u.error = ENOSPC;
    bad:
	sup->nfree = 0;
	prdev("No more space", dev);
	bdwrite(sb);
	return (0);
	}

       /*
	* Add block number bn to the freelist on device dev.
	*/
bfree(bn, dev)
	int  bn;
	int dev;
	{
	fast struct buf *sb, *fb;
	fast struct sup *sup;

	if (bn == 0)
		return;
	sb  = getsb(dev);
	sup = sb->data;
	if (bcheck(bn, sup, dev) == NO)
		goto done;
	if (sup->nfree == 0)
		{
		sup->free[0] = 0;
		sup->nfree = 1;
		}
	else if (sup->nfree >= 100)
		{
		fb = bget(bn, dev);
		copy(&sup->nfree, fb->data, 202);	/* PORT */
		bawrite(fb);
		sup->nfree = 0;
		}
	sup->free[sup->nfree++] = bn;
    done:
	bdwrite(sb);
	}

       /*
	* Check the validity of a file block number
	*/
bcheck(bn, sup, dev)
	int bn, dev;
	struct sup *sup;
	{
	if (sup->isize + 1 < bn && bn < sup->fsize)
		return YES;
	prdev("Out of range block number", dev);
	return NO;
	}