scsi: add free_request callback

Most device models have a simple lifecycle for the hba_private field
and they can free it when a request is completed or cancelled.
However, in some cases it may be simpler to tie the lifetime
of hba_private to that of the included SCSIRequest.  This patch
adds a free_request callback to SCSIBusInfo that lets an HBA
device model do exactly that.

Normally, device models use req->hba_private == NULL to flag requests
that have been completed already.  Device models that use free_request
will still need to track this using a flag.  This is the reason why
"converting" existing HBAs to use free_request adds complexity and
makes little sense.  It is simply an additional convenience that is
provided by the SCSI layer.  USB-attached storage will be the first
user.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

2 files changed, 6 insertions, 0 deletions

diff --git a/hw/scsi-bus.c b/hw/scsi-bus.c
index 5ad1013be1..dc7406389d 100644
--- a/hw/scsi-bus.c
+++ b/hw/scsi-bus.c
@@ -1354,6 +1354,7 @@ static const char *scsi_command_name(uint8_t cmd)
 
 SCSIRequest *scsi_req_ref(SCSIRequest *req)
 {
+    assert(req->refcount > 0);
     req->refcount++;
     return req;
 }
@@ -1362,6 +1363,10 @@ void scsi_req_unref(SCSIRequest *req)
 {
     assert(req->refcount > 0);
     if (--req->refcount == 0) {
+        SCSIBus *bus = DO_UPCAST(SCSIBus, qbus, req->dev->qdev.parent_bus);
+        if (bus->info->free_request && req->hba_private) {
+            bus->info->free_request(bus, req->hba_private);
+        }
         if (req->ops->free_req) {
             req->ops->free_req(req);
         }
diff --git a/hw/scsi.h b/hw/scsi.h
index 76f06d41de..367a346020 100644
--- a/hw/scsi.h
+++ b/hw/scsi.h
@@ -134,6 +134,7 @@ struct SCSIBusInfo {
 
     void (*save_request)(QEMUFile *f, SCSIRequest *req);
     void *(*load_request)(QEMUFile *f, SCSIRequest *req);
+    void (*free_request)(SCSIBus *bus, void *priv);
 };
 
 #define TYPE_SCSI_BUS "SCSI"