scsi: track per-SCSIRequest AioContext

Until now, a SCSIDevice's I/O requests have run in a single AioContext.
In order to support multiple IOThreads it will be necessary to move to
the concept of a per-SCSIRequest AioContext.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20250311132616.1049687-4-stefanha@redhat.com>
Tested-by: Peter Krempa <pkrempa@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

hw/scsi/scsi-bus.c

@@ -868,6 +868,7 @@ invalid_opcode:
         }
     }
 
+    req->ctx = qemu_get_current_aio_context();
     req->cmd = cmd;
     req->residual = req->cmd.xfer;
 

hw/scsi/scsi-disk.c

@@ -328,9 +328,8 @@ static void scsi_aio_complete(void *opaque, int ret)
     SCSIDiskReq *r = (SCSIDiskReq *)opaque;
     SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, r->req.dev);
 
-    /* The request must only run in the BlockBackend's AioContext */
-    assert(blk_get_aio_context(s->qdev.conf.blk) ==
-           qemu_get_current_aio_context());
+    /* The request must run in its AioContext */
+    assert(r->req.ctx == qemu_get_current_aio_context());
 
     assert(r->req.aiocb != NULL);
     r->req.aiocb = NULL;
@@ -430,12 +429,10 @@ static void scsi_dma_complete(void *opaque, int ret)
 
 static void scsi_read_complete_noio(SCSIDiskReq *r, int ret)
 {
-    SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, r->req.dev);
     uint32_t n;
 
-    /* The request must only run in the BlockBackend's AioContext */
-    assert(blk_get_aio_context(s->qdev.conf.blk) ==
-           qemu_get_current_aio_context());
+    /* The request must run in its AioContext */
+    assert(r->req.ctx == qemu_get_current_aio_context());
 
     assert(r->req.aiocb == NULL);
     if (scsi_disk_req_check_error(r, ret, ret > 0)) {
@@ -562,12 +559,10 @@ static void scsi_read_data(SCSIRequest *req)
 
 static void scsi_write_complete_noio(SCSIDiskReq *r, int ret)
 {
-    SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, r->req.dev);
     uint32_t n;
 
-    /* The request must only run in the BlockBackend's AioContext */
-    assert(blk_get_aio_context(s->qdev.conf.blk) ==
-           qemu_get_current_aio_context());
+    /* The request must run in its AioContext */
+    assert(r->req.ctx == qemu_get_current_aio_context());
 
     assert (r->req.aiocb == NULL);
     if (scsi_disk_req_check_error(r, ret, ret > 0)) {

include/hw/scsi/scsi.h

@@ -24,6 +24,7 @@ struct SCSIRequest {
     SCSIBus           *bus;
     SCSIDevice        *dev;
     const SCSIReqOps  *ops;
+    AioContext        *ctx;
     uint32_t          refcount;
     uint32_t          tag;
     uint32_t          lun;