+geteblk(size)
+ int size;
+{
+ register struct buf *bp, *flist;
+
+ if (size > MAXBSIZE)
+ panic("geteblk: size too big");
+loop:
+ bp = getnewbuf();
+ bp->b_flags |= B_INVAL;
+ bfree(bp);
+ bremhash(bp);
+ flist = &bfreelist[BQ_AGE];
+ binshash(bp, flist);
+ bp->b_dev = (dev_t)NODEV;
+ bp->b_error = 0;
+ if (brealloc(bp, size) == 0)
+ goto loop;
+ return(bp);
+}
+
+/*
+ * Allocate space associated with a buffer.
+ * If can't get space, buffer is released
+ */
+brealloc(bp, size)
+ register struct buf *bp;
+ int size;
+{
+ daddr_t start, last;
+ register struct buf *ep;
+ struct buf *dp;
+ int s;
+
+ /*
+ * First need to make sure that all overlaping previous I/O
+ * is dispatched with.
+ */
+ if (size == bp->b_bcount)
+ return (1);
+ if (size < bp->b_bcount) {
+ if (bp->b_flags & B_DELWRI) {
+ bwrite(bp);
+ return (0);
+ }
+ if (bp->b_flags & B_LOCKED)
+ panic("brealloc");
+ return (allocbuf(bp, size));
+ }
+ bp->b_flags &= ~B_DONE;
+ if (bp->b_dev == NODEV)
+ return (allocbuf(bp, size));
+
+ trace(TR_BREALLOC, pack(bp->b_dev, size), bp->b_blkno);
+ /*
+ * Search cache for any buffers that overlap the one that we
+ * are trying to allocate. Overlapping buffers must be marked
+ * invalid, after being written out if they are dirty. (indicated
+ * by B_DELWRI) A disk block must be mapped by at most one buffer
+ * at any point in time. Care must be taken to avoid deadlocking
+ * when two buffer are trying to get the same set of disk blocks.
+ */
+ start = bp->b_blkno;
+ last = start + btodb(size) - 1;
+ dp = BUFHASH(bp->b_dev, bp->b_blkno);
+loop:
+ for (ep = dp->b_forw; ep != dp; ep = ep->b_forw) {
+ if (ep == bp || ep->b_dev != bp->b_dev || (ep->b_flags&B_INVAL))
+ continue;
+ /* look for overlap */
+ if (ep->b_bcount == 0 || ep->b_blkno > last ||
+ ep->b_blkno + btodb(ep->b_bcount) <= start)
+ continue;
+ s = spl6();
+ if (ep->b_flags&B_BUSY) {
+ ep->b_flags |= B_WANTED;
+ sleep((caddr_t)ep, PRIBIO+1);
+ splx(s);
+ goto loop;
+ }
+ splx(s);
+ notavail(ep);
+ if (ep->b_flags & B_DELWRI) {
+ bwrite(ep);
+ goto loop;
+ }
+ ep->b_flags |= B_INVAL;
+ brelse(ep);
+ }
+ return (allocbuf(bp, size));
+}
+
+/*
+ * Find a buffer which is available for use.
+ * Select something from a free list.
+ * Preference is to AGE list, then LRU list.
+ */
+struct buf *
+getnewbuf()