From 8d0c3e9ea36396b7037449212526850054121c61 Mon Sep 17 00:00:00 2001
From: Will Sowerbutts <will@sowerbutts.com>
Date: Wed, 11 Feb 2015 19:58:45 +0000
Subject: [PATCH] Kernel: readi() - when reading whole sectors, transfer them
 directly into user memory.

---
 Kernel/inode.c | 40 ++++++++++++++++++++++++++--------------
 1 file changed, 26 insertions(+), 14 deletions(-)

diff --git a/Kernel/inode.c b/Kernel/inode.c
index ce34f2d4..d0ae1a83 100644
--- a/Kernel/inode.c
+++ b/Kernel/inode.c
@@ -11,6 +11,8 @@ void readi(inoptr ino, uint8_t flag)
 	unsigned char *bp;
 	uint16_t dev;
 	bool ispipe;
+	off_t uostash;
+	usize_t ucstash;
 
 	dev = ino->c_dev;
 	ispipe = false;
@@ -51,19 +53,29 @@ void readi(inoptr ino, uint8_t flag)
 
 	      loop:
 		while (toread) {
-			if ((pblk =
-			     bmap(ino, udata.u_offset >> BLKSHIFT,
-				  1)) != NULLBLK)
-				bp = bread(dev, pblk, 0);
-			else
-				bp = zerobuf();
-
-			amount =
-			    min(toread, BLKSIZE - (udata.u_offset&BLKMASK));
-
-			uputsys(bp + (udata.u_offset & BLKMASK), amount);
-
-			brelse(bp);
+			amount = min(toread, BLKSIZE - (udata.u_offset&BLKMASK));
+			pblk = bmap(ino, udata.u_offset >> BLKSHIFT, 1);
+
+			if(!ispipe && amount == BLKSIZE && bfind(dev, pblk) == 0){
+				/* we can transfer direct from disk to the userspace buffer */
+				uostash = udata.u_offset;	            /* stash file offset */
+				ucstash = udata.u_count;		    /* stash byte count */
+				udata.u_count = amount;                     /* transfer one sector */
+				udata.u_offset = ((off_t)pblk) << BLKSHIFT; /* replace with sector offset on device */
+				((*dev_tab[major(dev)].dev_read) (minor(dev), 1, 0)); /* read */
+				udata.u_offset = uostash;		    /* restore file offset */
+				udata.u_count = ucstash;                    /* restore byte count */
+			}else{
+				/* we transfer through the buffer pool */
+				if (pblk == NULLBLK)
+					bp = zerobuf();
+				else
+					bp = bread(dev, pblk, 0);
+
+				uputsys(bp + (udata.u_offset & BLKMASK), amount);
+
+				brelse(bp);
+			}
 
 			udata.u_base += amount;
 			udata.u_offset += amount;
@@ -145,7 +157,7 @@ void writei(inoptr ino, uint8_t flag)
 	      loop:
 
 		while (towrite) {
-			amount = min(towrite, 512 - (udata.u_offset&BLKMASK));
+			amount = min(towrite, BLKSIZE - (udata.u_offset&BLKMASK));
 
 			if ((pblk =
 			     bmap(ino, udata.u_offset >> BLKSHIFT,
-- 
2.34.1