From e34646ba6ce45a30688060f1bd6f305a25f3ec21 Mon Sep 17 00:00:00 2001
From: iiSaLMaN <slmanarendo1950@gmail.com>
Date: Sun, 2 Jun 2019 12:17:49 +0300
Subject: [PATCH] Add cached read function + some slight updates

---
 drivers/disk.c | 34 ++++++++++++++++++++++++++++++++--
 1 file changed, 32 insertions(+), 2 deletions(-)

diff --git a/drivers/disk.c b/drivers/disk.c
index 98c91a71..b4f12e9a 100644
--- a/drivers/disk.c
+++ b/drivers/disk.c
@@ -7,6 +7,7 @@
 
 #define SECTOR_SIZE 512
 
+static uint64_t last_sector = -1;
 static uint8_t sector_buf[512];
 
 static struct {
@@ -17,11 +18,11 @@ static struct {
     uint64_t lba;
 } dap = { 16, 1, 0, 0, 0 };
 
-int read_sector(int drive, int lba, int count, void *buffer) {
+int read_sector(int drive, void *buffer, uint64_t lba, size_t count) {
     dap.offset = (uint16_t)(size_t)sector_buf;
 
     while (count--) {
-        dap.lba = lba++;
+        dap.lba = lba;
         struct rm_regs r = {0};
         r.eax = 0x4200;
         r.edx = drive;
@@ -35,9 +36,38 @@ int read_sector(int drive, int lba, int count, void *buffer) {
         }
 
         memcpy(buffer, sector_buf, SECTOR_SIZE);
+        last_sector = lba++;
 
         buffer += SECTOR_SIZE;
     }
 
     return 0;
 }
+
+int read(int drive, void *buffer, int offset, size_t count) {
+    int res;
+    
+    if (last_sector == (uint64_t)-1)
+        if ((res = read_sector(drive, sector_buf, 0, 1)))
+            return res;
+    
+    uint64_t cur_sector = last_sector + (offset / SECTOR_SIZE);
+    offset %= SECTOR_SIZE;
+
+    size_t sectors_count = 1 + ((offset + count) / SECTOR_SIZE);
+
+    while (sectors_count--) {
+        if (cur_sector != last_sector)
+            if ((res = read_sector(drive, sector_buf, cur_sector, 1)))
+                return res;
+
+        size_t limited_count = ((offset + count) > SECTOR_SIZE) ? (size_t)(SECTOR_SIZE - offset) : count;
+        memcpy(buffer, &sector_buf[offset], limited_count);
+
+        offset = (offset + limited_count) % SECTOR_SIZE;
+        buffer += limited_count;
+        cur_sector++;
+    }
+
+    return 0;
+}