- for (ep = &buf[bufhash[i]]; ep != &buf[-1];
- ep = &buf[ep->b_hlink])
- if (ep->b_hlink == x) {
- ep->b_hlink = bp->b_hlink;
- return;
+ 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 = splbio();
+ 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;