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

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

[Christoph Hellwig]

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;

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

[Kevin Wolf]

Am 06.05.2010 22:04, schrieb Christoph Hellwig:
> 
> Use pread instead of lseek + read in preparation of using the qemu
> block API.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Thanks, applied both patches to the block branch.

We'll probably have to live with the fact that we can't test changes to
the parallels driver and need to trust patch review.

Kevin