[Qemu-devel] [RFC PATCH 8/9] scsi: add get_iovec/unmap_iovec to SCSIBusOps

[Paolo Bonzini <pbonzini@redhat.com>]

This lets scsi-disk avoid a bounce buffer.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/scsi-bus.c  |   16 ++++++++++++----
 hw/scsi-disk.c |   21 ++++++++++++++++-----
 hw/scsi.h      |    3 +++
 3 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/hw/scsi-bus.c b/hw/scsi-bus.c
index 3b545ed..8e888e8 100644
--- a/hw/scsi-bus.c
+++ b/hw/scsi-bus.c
@@ -618,6 +618,8 @@ void scsi_req_unref(SCSIRequest *req)
         if (req->dev->info->free_req) {
             req->dev->info->free_req(req);
         }
+        qemu_iovec_reset(&req->qiov);
+        qemu_iovec_destroy(&req->qiov);
         qemu_free(req);
     }
 }
@@ -634,13 +636,19 @@ void scsi_req_continue(SCSIRequest *req)
     }
 }
 
-/* Called by the devices when data is ready for the HBA.  The HBA should
-   start a DMA operation to read or fill the device's data buffer.
-   Once it completes, calling scsi_req_continue will restart I/O.  */
+/* Called by the devices when data is ready for the HBA.  Depending on
+   the transfer method it will call either unmap_iovec or transfer_data.
+   Execution of the command resumes when the HBA calls scsi_req_continue;
+   if applicable, the HBA should do so only after completing any DMA
+   operations involving the request buffer.  */
 void scsi_req_data(SCSIRequest *req, int len)
 {
     trace_scsi_req_data(req->dev->id, req->lun, req->tag, len);
-    req->bus->ops->transfer_data(req, len);
+    if (req->has_sg_list) {
+        req->bus->ops->unmap_iovec(req, len);
+    } else {
+        req->bus->ops->transfer_data(req, len);
+    }
 }
 
 void scsi_req_print(SCSIRequest *req)
diff --git a/hw/scsi-disk.c b/hw/scsi-disk.c
index 4f5ba1c..e13b633 100644
--- a/hw/scsi-disk.c
+++ b/hw/scsi-disk.c
@@ -139,12 +139,23 @@ static uint32_t scsi_init_iovec(SCSIDiskReq *r)
 {
     SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, r->req.dev);
 
-    if (!r->iov.iov_base) {
-        r->buflen = SCSI_DMA_BUF_SIZE;
-        r->iov.iov_base = qemu_blockalign(s->bs, r->buflen);
+    qemu_iovec_reset(&r->req.qiov);
+    if (r->req.bus->ops->get_iovec) {
+        r->req.bus->ops->get_iovec(&r->req, r->sector_count * 512);
+    }
+    if (r->req.qiov.size) {
+        assert((r->req.qiov.size % 512) == 0);
+        r->req.has_sg_list = true;
+    } else {
+        if (!r->iov.iov_base) {
+            r->buflen = SCSI_DMA_BUF_SIZE;
+            r->iov.iov_base = qemu_blockalign(s->bs, r->buflen);
+        }
+        r->iov.iov_len = MIN(r->sector_count * 512, r->buflen);
+        qemu_iovec_destroy(&r->req.qiov);
+        qemu_iovec_init_external(&r->req.qiov, &r->iov, 1);
+        r->req.has_sg_list = false;
     }
-    r->iov.iov_len = MIN(r->sector_count * 512, r->buflen);
-    qemu_iovec_init_external(&r->req.qiov, &r->iov, 1);
     return r->req.qiov.size / 512;
 }
 
diff --git a/hw/scsi.h b/hw/scsi.h
index b551b57..9627404 100644
--- a/hw/scsi.h
+++ b/hw/scsi.h
@@ -35,6 +35,7 @@ struct SCSIRequest {
     uint32_t          tag;
     uint32_t          lun;
     uint32_t          status;
+    bool              has_sg_list;
     struct {
         uint8_t buf[SCSI_CMD_BUF_SIZE];
         int len;
@@ -82,6 +83,8 @@ struct SCSIBusOps {
     void (*transfer_data)(SCSIRequest *req, uint32_t arg);
     void (*complete)(SCSIRequest *req, uint32_t arg);
     void (*cancel)(SCSIRequest *req);
+    void (*get_iovec)(SCSIRequest *req, uint64_t len);
+    void (*unmap_iovec)(SCSIRequest *req, uint64_t len);
 };
 
 struct SCSIBus {
-- 
1.7.4.4