block-vbd: implement support for splitting requests

the main issue with stubdoms at the moment is that the new dma api does
not support an upper limit for the number of sectors in a single dma
transfer.
This means that block-vbd can issue blkfront_aio transfers that exceed
the blktap limit BLKIF_MAX_SEGMENTS_PER_REQUEST.
The attached qemu patch makes block-vbd split any request bigger than
the limit above.

The small xen patch is also needed to change struct blkfront_aiocb.
 [ The corresponding changeset in xen-unstable is 19463:f2cf89a4e762 -iwj ]

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

diff --git a/block-vbd.c b/block-vbd.c
index 8c15d65b6171de05fafb004b479561b97f41e190..0e70ef2500e8b62fd3d0269aa1354f3c3aec88d9 100644 (file)
--- a/block-vbd.c
+++ b/block-vbd.c
@@ -31,6 +31,10 @@
 #include <malloc.h>
 #include "qemu-char.h"
 
+#include <xen/io/blkif.h>
+#define IDE_DMA_BUF_SECTORS \
+       (((BLKIF_MAX_SEGMENTS_PER_REQUEST - 1 ) * TARGET_PAGE_SIZE) / 512)
+#define IDE_DMA_BUF_BYTES (IDE_DMA_BUF_SECTORS * 512)
 #define SECTOR_SIZE 512
 
 #ifndef QEMU_TOOL
@@ -131,8 +135,18 @@ void qemu_aio_wait(void)
     remove_waiter(w);
 }
 
-static void vbd_aio_callback(struct blkfront_aiocb *aiocbp, int ret) {
+static void vbd_do_aio(struct blkfront_aiocb *aiocbp, int ret) {
     VbdAIOCB *acb = aiocbp->data;
+    int n = aiocbp->aio_nbytes;
+
+    aiocbp->total_bytes -= n;
+    if (aiocbp->total_bytes > 0) {
+        aiocbp->aio_buf += n; 
+        aiocbp->aio_offset += n;
+        aiocbp->aio_nbytes = aiocbp->total_bytes > IDE_DMA_BUF_BYTES ? IDE_DMA_BUF_BYTES : aiocbp->total_bytes;
+        blkfront_aio(aiocbp, aiocbp->is_write);
+        return;
+    }
 
     acb->common.cb(acb->common.opaque, ret);
     qemu_aio_release(acb);
@@ -140,7 +154,7 @@ static void vbd_aio_callback(struct blkfront_aiocb *aiocbp, int ret) {
 
 static VbdAIOCB *vbd_aio_setup(BlockDriverState *bs,
         int64_t sector_num, uint8_t *buf, int nb_sectors,
-        BlockDriverCompletionFunc *cb, void *opaque)
+        BlockDriverCompletionFunc *cb, uint8_t is_write, void *opaque)
 {
     BDRVVbdState *s = bs->opaque;
     VbdAIOCB *acb;
@@ -150,9 +164,15 @@ static VbdAIOCB *vbd_aio_setup(BlockDriverState *bs,
        return NULL;
     acb->aiocb.aio_dev = s->dev;
     acb->aiocb.aio_buf = buf;
-    acb->aiocb.aio_nbytes = nb_sectors * SECTOR_SIZE;
     acb->aiocb.aio_offset = sector_num * SECTOR_SIZE;
-    acb->aiocb.aio_cb = vbd_aio_callback;
+    if (nb_sectors <= IDE_DMA_BUF_SECTORS)
+        acb->aiocb.aio_nbytes = nb_sectors * 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.is_write = is_write;
     acb->aiocb.data = acb;
 
     return acb;
@@ -164,7 +184,7 @@ static BlockDriverAIOCB *vbd_aio_read(BlockDriverState *bs,
 {
     VbdAIOCB *acb;
 
-    acb = vbd_aio_setup(bs, sector_num, buf, nb_sectors, cb, opaque);
+    acb = vbd_aio_setup(bs, sector_num, buf, nb_sectors, cb, 0, opaque);
     if (!acb)
        return NULL;
     blkfront_aio(&acb->aiocb, 0);
@@ -177,7 +197,7 @@ static BlockDriverAIOCB *vbd_aio_write(BlockDriverState *bs,
 {
     VbdAIOCB *acb;
 
-    acb = vbd_aio_setup(bs, sector_num, (uint8_t*) buf, nb_sectors, cb, opaque);
+    acb = vbd_aio_setup(bs, sector_num, (uint8_t*) buf, nb_sectors, cb, 1, opaque);
     if (!acb)
        return NULL;
     blkfront_aio(&acb->aiocb, 1);
@@ -196,7 +216,7 @@ static int vbd_aligned_io(BlockDriverState *bs,
     VbdAIOCB *acb;
     int result[2];
     result[0] = 0;
-    acb = vbd_aio_setup(bs, sector_num, (uint8_t*) buf, nb_sectors, vbd_cb, &result);
+    acb = vbd_aio_setup(bs, sector_num, (uint8_t*) buf, nb_sectors, vbd_cb, write, &result);
     blkfront_aio(&acb->aiocb, write);
     while (!result[0])
        qemu_aio_wait();
@@ -268,13 +288,13 @@ static BlockDriverAIOCB *vbd_aio_flush(BlockDriverState *bs,
     }
     if (s->info.barrier == 1) {
         acb = vbd_aio_setup(bs, 0, NULL, 0,
-                s->info.flush == 1 ? vbd_nop_cb : cb, opaque);
+                s->info.flush == 1 ? vbd_nop_cb : cb, 0, opaque);
         if (!acb)
             return NULL;
         blkfront_aio_push_operation(&acb->aiocb, BLKIF_OP_WRITE_BARRIER);
     }
     if (s->info.flush == 1) {
-        acb = vbd_aio_setup(bs, 0, NULL, 0, cb, opaque);
+        acb = vbd_aio_setup(bs, 0, NULL, 0, cb, 0, opaque);
         if (!acb)
             return NULL;
         blkfront_aio_push_operation(&acb->aiocb, BLKIF_OP_FLUSH_DISKCACHE);