xfs: pass the actual offset and len to allocate to xfs_bmapi_allocate

xfs_bmapi_allocate currently overwrites offset and len when converting
delayed allocations, and duplicates the length cap done for non-delalloc
allocations.  Move all that logic into the callers to avoid duplication
and to make the calling conventions more obvious.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

fs/xfs/libxfs/xfs_bmap.c

@@ -4185,21 +4185,11 @@ xfs_bmapi_allocate(
 	int			error;
 
 	ASSERT(bma->length > 0);
+	ASSERT(bma->length <= XFS_MAX_BMBT_EXTLEN);
 
-	/*
-	 * For the wasdelay case, we could also just allocate the stuff asked
-	 * for in this bmap call but that wouldn't be as good.
-	 */
 	if (bma->wasdel) {
-		bma->length = (xfs_extlen_t)bma->got.br_blockcount;
-		bma->offset = bma->got.br_startoff;
 		if (!xfs_iext_peek_prev_extent(ifp, &bma->icur, &bma->prev))
 			bma->prev.br_startoff = NULLFILEOFF;
-	} else {
-		bma->length = XFS_FILBLKS_MIN(bma->length, XFS_MAX_BMBT_EXTLEN);
-		if (!bma->eof)
-			bma->length = XFS_FILBLKS_MIN(bma->length,
-					bma->got.br_startoff - bma->offset);
 	}
 
 	if (bma->flags & XFS_BMAPI_CONTIG)
@@ -4533,6 +4523,15 @@ xfs_bmapi_write(
 			 */
 			bma.length = XFS_FILBLKS_MIN(len, XFS_MAX_BMBT_EXTLEN);
 
+			if (wasdelay) {
+				bma.offset = bma.got.br_startoff;
+				bma.length = bma.got.br_blockcount;
+			} else {
+				if (!eof)
+					bma.length = XFS_FILBLKS_MIN(bma.length,
+						bma.got.br_startoff - bno);
+			}
+
 			ASSERT(bma.length > 0);
 			error = xfs_bmapi_allocate(&bma);
 			if (error) {
@@ -4686,11 +4685,16 @@ xfs_bmapi_convert_one_delalloc(
 	bma.tp = tp;
 	bma.ip = ip;
 	bma.wasdel = true;
-	bma.offset = bma.got.br_startoff;
-	bma.length = max_t(xfs_filblks_t, bma.got.br_blockcount,
-			XFS_MAX_BMBT_EXTLEN);
 	bma.minleft = xfs_bmapi_minleft(tp, ip, whichfork);
 
+	/*
+	 * Always allocate convert from the start of the delalloc extent even if
+	 * that is outside the passed in range to create large contiguous
+	 * extents on disk.
+	 */
+	bma.offset = bma.got.br_startoff;
+	bma.length = bma.got.br_blockcount;
+
 	/*
 	 * When we're converting the delalloc reservations backing dirty pages
 	 * in the page cache, we must be careful about how we create the new