[Qemu-devel] [PATCH 1/2] parallels: use pread

[Christoph Hellwig <hch@lst.de>]

Use pread instead of lseek + read in preparation of using the qemu
block API.

Signed-off-by: Christoph Hellwig <hch@lst.de>

Index: qemu-kevin/block/parallels.c
===================================================================
--- qemu-kevin.orig/block/parallels.c	2010-05-06 21:59:25.809255629 +0200
+++ qemu-kevin/block/parallels.c	2010-05-06 22:01:11.343284544 +0200
@@ -83,7 +83,7 @@ static int parallels_open(BlockDriverSta
 
     s->fd = fd;
 
-    if (read(fd, &ph, sizeof(ph)) != sizeof(ph))
+    if (pread(fd, &ph, sizeof(ph), 0) != sizeof(ph))
         goto fail;
 
     if (memcmp(ph.magic, HEADER_MAGIC, 16) ||
@@ -93,14 +93,11 @@ static int parallels_open(BlockDriverSta
 
     bs->total_sectors = le32_to_cpu(ph.nb_sectors);
 
-    if (lseek(s->fd, 64, SEEK_SET) != 64)
-	goto fail;
-
     s->tracks = le32_to_cpu(ph.tracks);
 
     s->catalog_size = le32_to_cpu(ph.catalog_entries);
     s->catalog_bitmap = qemu_malloc(s->catalog_size * 4);
-    if (read(s->fd, s->catalog_bitmap, s->catalog_size * 4) !=
+    if (pread(s->fd, s->catalog_bitmap, s->catalog_size * 4, 64) !=
 	s->catalog_size * 4)
 	goto fail;
     for (i = 0; i < s->catalog_size; i++)
@@ -114,28 +111,18 @@ fail:
     return -1;
 }
 
-static inline int seek_to_sector(BlockDriverState *bs, int64_t sector_num)
+static int64_t seek_to_sector(BlockDriverState *bs, int64_t sector_num)
 {
     BDRVParallelsState *s = bs->opaque;
     uint32_t index, offset;
-    uint64_t position;
 
     index = sector_num / s->tracks;
     offset = sector_num % s->tracks;
 
-    // not allocated
+    /* not allocated */
     if ((index > s->catalog_size) || (s->catalog_bitmap[index] == 0))
 	return -1;
-
-    position = (uint64_t)(s->catalog_bitmap[index] + offset) * 512;
-
-//    fprintf(stderr, "sector: %llx index=%x offset=%x pointer=%x position=%x\n",
-//	sector_num, index, offset, s->catalog_bitmap[index], position);
-
-    if (lseek(s->fd, position, SEEK_SET) != position)
-	return -1;
-
-    return 0;
+    return (uint64_t)(s->catalog_bitmap[index] + offset) * 512;
 }
 
 static int parallels_read(BlockDriverState *bs, int64_t sector_num,
@@ -144,11 +131,13 @@ static int parallels_read(BlockDriverSta
     BDRVParallelsState *s = bs->opaque;
 
     while (nb_sectors > 0) {
-	if (!seek_to_sector(bs, sector_num)) {
-	    if (read(s->fd, buf, 512) != 512)
-		return -1;
-	} else
+        int64_t position = seek_to_sector(bs, sector_num);
+        if (position >= 0) {
+            if (pread(s->fd, buf, 512, position) != 512)
+                return -1;
+        } else {
             memset(buf, 0, 512);
+        }
         nb_sectors--;
         sector_num++;
         buf += 512;