WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

[Xen-devel] [PATCH 2 of 2] qemu block-vbd: bounce misaligned read\write

To: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] [PATCH 2 of 2] qemu block-vbd: bounce misaligned read\write requests
From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Date: Thu, 21 May 2009 12:41:10 +0100
Delivery-date: Thu, 21 May 2009 04:40:44 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Thunderbird 2.0.0.14 (X11/20080505)
Bounce any read or write request with a buffer not aligned, a sector
number not aligned or an offset not aligned according to the sector size
reported by blkfront.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> 

---

diff --git a/block-vbd.c b/block-vbd.c
index 0e70ef2..89ecf44 100644
--- a/block-vbd.c
+++ b/block-vbd.c
@@ -88,8 +88,12 @@ static int vbd_open(BlockDriverState *bs, const char 
*filename, int flags)
     if (!s->dev)
        return -EIO;
 
-    if (SECTOR_SIZE % s->info.sector_size) {
-       printf("sector size is %d, we only support sector sizes that divide 
%d\n", s->info.sector_size, SECTOR_SIZE);
+    if (s->info.sector_size % SECTOR_SIZE) {
+       printf("sector size is %d, we only support sector sizes that are 
multiple of %d\n", s->info.sector_size, SECTOR_SIZE);
+       return -EIO;
+    }
+    if (PAGE_SIZE % s->info.sector_size) {
+       printf("sector size is %d, we only support sector sizes that divide 
%llu\n", s->info.sector_size, PAGE_SIZE);
        return -EIO;
     }
 
@@ -101,8 +105,16 @@ static int vbd_open(BlockDriverState *bs, const char 
*filename, int flags)
     return 0;
 }
 
+struct vbd_align {
+    uint8_t *src;
+    uint8_t *dst;
+    int64_t offset;
+    int bytes;
+};
+
 typedef struct VbdAIOCB {
     BlockDriverAIOCB common;
+    struct vbd_align align;
     struct blkfront_aiocb aiocb;
 } VbdAIOCB;
 
@@ -147,31 +159,77 @@ static void vbd_do_aio(struct blkfront_aiocb *aiocbp, int 
ret) {
         blkfront_aio(aiocbp, aiocbp->is_write);
         return;
     }
+    if (acb->align.bytes)
+        memcpy(acb->align.dst, acb->align.src + acb->align.offset, 
acb->align.bytes);
+    if (acb->align.src)
+        qemu_free(acb->align.src);
 
     acb->common.cb(acb->common.opaque, ret);
     qemu_aio_release(acb);
 }
 
+static int vbd_read(BlockDriverState *bs, int64_t sector_num, uint8_t *buf, 
int nb_sectors);
+
 static VbdAIOCB *vbd_aio_setup(BlockDriverState *bs,
         int64_t sector_num, uint8_t *buf, int nb_sectors,
         BlockDriverCompletionFunc *cb, uint8_t is_write, void *opaque)
 {
     BDRVVbdState *s = bs->opaque;
     VbdAIOCB *acb;
+    int64_t sector_num_aligned  = sector_num;
+    int nb_sectors_aligned = nb_sectors;
+    uint8_t *buf_aligned = buf;
+    int sector_alignment_offset = 0;
+    int misalign = 0;
 
     acb = qemu_aio_get(bs, cb, opaque);
     if (!acb)
        return NULL;
+
+    memset(&acb->align, 0x00, sizeof(struct vbd_align));
+    /* non-sector-aligned location */
+    if ((sector_num * SECTOR_SIZE) & (s->info.sector_size - 1)) {
+        sector_num_aligned = sector_num & (~((s->info.sector_size >> 9) - 1));
+        sector_alignment_offset = sector_num - sector_num_aligned;
+        misalign = 1;
+    }
+    /* non-sector-sized amounts */
+    if ((nb_sectors * SECTOR_SIZE) & (s->info.sector_size - 1)) {
+        nb_sectors_aligned = (nb_sectors + (s->info.sector_size / SECTOR_SIZE 
- 1)) & (~((s->info.sector_size >> 9) - 1));
+        misalign = 1;
+    }
+    /* non-sector-aligned buffer */
+    if (misalign || ((uintptr_t)buf & (s->info.sector_size - 1))) {
+        int sm = s->info.sector_size / SECTOR_SIZE;
+        nb_sectors_aligned += sector_alignment_offset;
+        buf_aligned = qemu_memalign(s->info.sector_size, nb_sectors_aligned * 
SECTOR_SIZE);
+        if (is_write) {
+            if (sector_alignment_offset > 0)
+                vbd_read(bs, sector_num_aligned, buf_aligned, sm);
+            if (nb_sectors_aligned != nb_sectors)
+                vbd_read(bs, sector_num_aligned + nb_sectors_aligned - sm,
+                         buf_aligned + (nb_sectors_aligned - sm) * SECTOR_SIZE,
+                         sm);
+            memcpy(buf_aligned + (sector_alignment_offset * SECTOR_SIZE), buf, 
nb_sectors * SECTOR_SIZE);
+            acb->align.src = buf_aligned;
+        } else {
+            acb->align.src = buf_aligned;
+            acb->align.dst = buf;
+            acb->align.offset = sector_alignment_offset * SECTOR_SIZE;
+            acb->align.bytes = nb_sectors * SECTOR_SIZE;
+        }
+    }
+
     acb->aiocb.aio_dev = s->dev;
-    acb->aiocb.aio_buf = buf;
-    acb->aiocb.aio_offset = sector_num * SECTOR_SIZE;
+    acb->aiocb.aio_buf = buf_aligned;
+    acb->aiocb.aio_offset = sector_num_aligned * SECTOR_SIZE;
     if (nb_sectors <= IDE_DMA_BUF_SECTORS)
-        acb->aiocb.aio_nbytes = nb_sectors * SECTOR_SIZE;
+        acb->aiocb.aio_nbytes = nb_sectors_aligned * SECTOR_SIZE;
     else
         acb->aiocb.aio_nbytes = IDE_DMA_BUF_BYTES;
     acb->aiocb.aio_cb = vbd_do_aio;
 
-    acb->aiocb.total_bytes = nb_sectors * SECTOR_SIZE;
+    acb->aiocb.total_bytes = nb_sectors_aligned * SECTOR_SIZE;
     acb->aiocb.is_write = is_write;
     acb->aiocb.data = acb;
 
@@ -226,41 +284,13 @@ static int vbd_aligned_io(BlockDriverState *bs,
 static int vbd_read(BlockDriverState *bs,
        int64_t sector_num, uint8_t *buf, int nb_sectors)
 {
-    uint8_t *iobuf;
-    int ret;
-    /* page alignment would be a bit better, but that's still fine compared to
-     * copying */
-    if (!((uintptr_t)buf & (SECTOR_SIZE-1)))
-       return vbd_aligned_io(bs, sector_num, buf, nb_sectors, 0);
-    iobuf = qemu_memalign(PAGE_SIZE, nb_sectors * SECTOR_SIZE);
-    ret = vbd_aligned_io(bs, sector_num, iobuf, nb_sectors, 0);
-    memcpy(buf, iobuf, nb_sectors * SECTOR_SIZE);
-    free(iobuf);
-    if (ret < 0)
-       return ret;
-    else if (ret != nb_sectors * SECTOR_SIZE)
-       return -EINVAL;
-    else
-       return 0;
+    return vbd_aligned_io(bs, sector_num, buf, nb_sectors, 0);
 }
 
 static int vbd_write(BlockDriverState *bs,
        int64_t sector_num, const uint8_t *buf, int nb_sectors)
 {
-    uint8_t *iobuf;
-    int ret;
-    if (!((uintptr_t)buf & (SECTOR_SIZE-1)))
-       return vbd_aligned_io(bs, sector_num, (uint8_t*) buf, nb_sectors, 1);
-    iobuf = qemu_memalign(PAGE_SIZE, nb_sectors * SECTOR_SIZE);
-    memcpy(iobuf, buf, nb_sectors * SECTOR_SIZE);
-    ret = vbd_aligned_io(bs, sector_num, iobuf, nb_sectors, 1);
-    free(iobuf);
-    if (ret < 0)
-       return ret;
-    else if (ret != nb_sectors * SECTOR_SIZE)
-       return -EINVAL;
-    else
-       return 0;
+    return vbd_aligned_io(bs, sector_num, (uint8_t*) buf, nb_sectors, 1);
 }
 
 static void vbd_aio_cancel(BlockDriverAIOCB *blockacb)

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel

<Prev in Thread] Current Thread [Next in Thread>
  • [Xen-devel] [PATCH 2 of 2] qemu block-vbd: bounce misaligned read\write requests, Stefano Stabellini <=