Patchwork [1/6] bochs: use pread

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Submitter Christoph Hellwig
Date May 4, 2010, 10:44 a.m.
Message ID <20100504104408.GA6388@lst.de>
Download mbox | patch
Permalink /patch/51579/
State New
Headers show

Comments

Christoph Hellwig - May 4, 2010, 10:44 a.m.
Use pread instead of lseek + read in preparation of using the qemu
block API.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Roy Tam - May 4, 2010, 11:20 a.m.
2010/5/4 Christoph Hellwig <hch@lst.de>:
> Use pread instead of lseek + read in preparation of using the qemu
> block API.
>

IIRC there is no pread in MinGW.
Christoph Hellwig - May 4, 2010, 11:39 a.m.
On Tue, May 04, 2010 at 07:20:22PM +0800, Roy Tam wrote:
> 2010/5/4 Christoph Hellwig <hch@lst.de>:
> > Use pread instead of lseek + read in preparation of using the qemu
> > block API.
> >
> 
> IIRC there is no pread in MinGW.

It gets replaced in the next patch anyway.
Anthony Liguori - May 5, 2010, 1:17 p.m.
On 05/04/2010 05:44 AM, Christoph Hellwig wrote:
> Use pread instead of lseek + read in preparation of using the qemu
> block API.
>
> Signed-off-by: Christoph Hellwig<hch@lst.de>
>    

Looks good to me.

Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>

Regards,

Anthony Liguori

> Index: qemu-kevin/block/bochs.c
> ===================================================================
> --- qemu-kevin.orig/block/bochs.c	2010-05-03 12:58:53.419012621 +0200
> +++ qemu-kevin/block/bochs.c	2010-05-03 12:59:13.873005360 +0200
> @@ -125,7 +125,7 @@ static int bochs_open(BlockDriverState *
>
>       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->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 *
>       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) {
> +    /* read in bitmap for current extent */
> +    if (pread(s->fd,&bitmap_entry, 1, bitmap_offset + (extent_offset / 8))
> +            != 1) {
>           return -1;
>       }
>
> -    if (read(s->fd,&bitmap_entry, 1) != 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 (!((bitmap_entry>>  (extent_offset % 8))&  1)) {
> +	return -1; /* not allocated */
>       }
>
> -    if (lseek(s->fd, block_offset, SEEK_SET) == (off_t)-1) {
> -        return -1;
> -    }
> -
> -    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 *
>       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++;
>
>
>
>

Patch

Index: qemu-kevin/block/bochs.c
===================================================================
--- qemu-kevin.orig/block/bochs.c	2010-05-03 12:58:53.419012621 +0200
+++ qemu-kevin/block/bochs.c	2010-05-03 12:59:13.873005360 +0200
@@ -125,7 +125,7 @@  static int bochs_open(BlockDriverState *
 
     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->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 *
     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) {
+    /* read in bitmap for current extent */
+    if (pread(s->fd, &bitmap_entry, 1, bitmap_offset + (extent_offset / 8))
+            != 1) {
         return -1;
     }
 
-    if (read(s->fd, &bitmap_entry, 1) != 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 (!((bitmap_entry >> (extent_offset % 8)) & 1)) {
+	return -1; /* not allocated */
     }
 
-    if (lseek(s->fd, block_offset, SEEK_SET) == (off_t)-1) {
-        return -1;
-    }
-
-    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 *
     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++;