ext2load: increase read speed

This patch dramatically drops the amount of time u-boot needs to read a
file from an ext2 partition.  On a typical 2 to 5 MB file (kernels and
initrds) it goes from tens of seconds to a couple seconds.

All we are doing here is grouping contiguous blocks into one read.

Boot tested on Globalscale Technologies Dreamplug (Kirkwood ARM SoC)
with three different files.  sha1sums were calculated in Linux
userspace, and then confirmed after ext2load.
Signed-off-by: NJason Cooper <u-boot@lakedaemon.net>
Tested-by: NEric Nelson <eric.nelson@boundarydevices.com>
Tested-by: NThierry Reding <thierry.reding@avionic-design.de>

fs/ext2/ext2fs.c

@@ -420,7 +420,6 @@ int ext2fs_read_file
 		if (blknr < 0) {
 			return (-1);
 		}
-		blknr = blknr << log2blocksize;
 
 		/* Last block.  */
 		if (i == blockcnt - 1) {
@@ -438,6 +437,29 @@ int ext2fs_read_file
 			blockend -= skipfirst;
 		}
 
+		/* grab middle blocks in one go */
+		if (i != pos / blocksize && i != blockcnt - 1 && blockcnt > 3) {
+			int oldblk = blknr;
+			int blocknxt;
+			while (i < blockcnt - 1) {
+				blocknxt = ext2fs_read_block(node, i + 1);
+				if (blocknxt == (oldblk + 1)) {
+					oldblk = blocknxt;
+					i++;
+				} else {
+					blocknxt = ext2fs_read_block(node, i);
+					break;
+				}
+			}
+
+			if (oldblk == blknr)
+				blockend = blocksize;
+			else
+				blockend = (1 + blocknxt - blknr) * blocksize;
+		}
+
+		blknr = blknr << log2blocksize;
+
 		/* If the block number is 0 this block is not stored on disk but
 		   is zero filled instead.  */
 		if (blknr) {
@@ -450,7 +472,7 @@ int ext2fs_read_file
 		} else {
 			memset (buf, 0, blocksize - skipfirst);
 		}
-		buf += blocksize - skipfirst;
+		buf += blockend - skipfirst;
 	}
 	return (len);
 }