bochs: use pread

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

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/bochs.c

@@ -125,7 +125,7 @@ static int bochs_open(BlockDriverState *bs, const char *filename, int flags)
 
     s->fd = fd;
 
-    if (read(fd, &bochs, sizeof(bochs)) != sizeof(bochs)) {
+    if (pread(fd, &bochs, sizeof(bochs), 0) != sizeof(bochs)) {
         goto fail;
     }
 
@@ -144,14 +144,10 @@ static int bochs_open(BlockDriverState *bs, const char *filename, int flags)
       bs->total_sectors = le64_to_cpu(bochs.extra.redolog.disk) / 512;
     }
 
-    if (lseek(s->fd, le32_to_cpu(bochs.header), SEEK_SET) == (off_t)-1) {
-        goto fail;
-    }
-
     s->catalog_size = le32_to_cpu(bochs.extra.redolog.catalog);
     s->catalog_bitmap = qemu_malloc(s->catalog_size * 4);
-    if (read(s->fd, s->catalog_bitmap, s->catalog_size * 4) !=
-	s->catalog_size * 4)
+    if (pread(s->fd, s->catalog_bitmap, s->catalog_size * 4,
+              le32_to_cpu(bochs.header)) != s->catalog_size * 4)
 	goto fail;
     for (i = 0; i < s->catalog_size; i++)
 	le32_to_cpus(&s->catalog_bitmap[i]);
@@ -169,54 +165,35 @@ static int bochs_open(BlockDriverState *bs, const char *filename, int flags)
     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)
 {
     BDRVBochsState *s = bs->opaque;
     int64_t offset = sector_num * 512;
-    int64_t extent_index, extent_offset, bitmap_offset, block_offset;
+    int64_t extent_index, extent_offset, bitmap_offset;
     char bitmap_entry;
 
     // seek to sector
     extent_index = offset / s->extent_size;
     extent_offset = (offset % s->extent_size) / 512;
 
-    if (s->catalog_bitmap[extent_index] == 0xffffffff)
-    {
-//	fprintf(stderr, "page not allocated [%x - %x:%x]\n",
-//	    sector_num, extent_index, extent_offset);
-	return -1; // not allocated
+    if (s->catalog_bitmap[extent_index] == 0xffffffff) {
+	return -1; /* not allocated */
     }
 
     bitmap_offset = s->data_offset + (512 * s->catalog_bitmap[extent_index] *
 	(s->extent_blocks + s->bitmap_blocks));
-    block_offset = bitmap_offset + (512 * (s->bitmap_blocks + extent_offset));
-
-//    fprintf(stderr, "sect: %x [ext i: %x o: %x] -> %x bitmap: %x block: %x\n",
-//	sector_num, extent_index, extent_offset,
-//	le32_to_cpu(s->catalog_bitmap[extent_index]),
-//	bitmap_offset, block_offset);
-
-    // read in bitmap for current extent
-    if (lseek(s->fd, bitmap_offset + (extent_offset / 8), SEEK_SET) ==
-        (off_t)-1) {
-        return -1;
-    }
 
-    if (read(s->fd, &bitmap_entry, 1) != 1)
+    /* read in bitmap for current extent */
+    if (pread(s->fd, &bitmap_entry, 1, bitmap_offset + (extent_offset / 8))
+            != 1) {
         return -1;
-
-    if (!((bitmap_entry >> (extent_offset % 8)) & 1))
-    {
-//	fprintf(stderr, "sector (%x) in bitmap not allocated\n",
-//	    sector_num);
-	return -1; // not allocated
     }
 
-    if (lseek(s->fd, block_offset, SEEK_SET) == (off_t)-1) {
-        return -1;
+    if (!((bitmap_entry >> (extent_offset % 8)) & 1)) {
+	return -1; /* not allocated */
     }
 
-    return 0;
+    return bitmap_offset + (512 * (s->bitmap_blocks + extent_offset));
 }
 
 static int bochs_read(BlockDriverState *bs, int64_t sector_num,
@@ -226,13 +203,13 @@ static int bochs_read(BlockDriverState *bs, int64_t sector_num,
     int ret;
 
     while (nb_sectors > 0) {
-	if (!seek_to_sector(bs, sector_num))
-	{
-	    ret = read(s->fd, buf, 512);
-	    if (ret != 512)
-		return -1;
-	}
-	else
+        int64_t block_offset = seek_to_sector(bs, sector_num);
+        if (block_offset >= 0) {
+            ret = pread(s->fd, buf, 512, block_offset);
+            if (ret != 512) {
+                return -1;
+            }
+        } else
             memset(buf, 0, 512);
         nb_sectors--;
         sector_num++;