scsi-disk: Add warning comments that host_status errors take a shortcut

scsi_block_sgio_complete() has surprising behaviour in that there are
error cases in which it directly completes the request and never calls
the passed callback. In the current state of the code, this doesn't seem
to result in bugs, but with future code changes, we must be careful to
never rely on the callback doing some cleanup until this code smell is
fixed. For now, just add warnings to make people aware of the trap.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20240731123207.27636-4-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
index 6e1a5c98df..69a195177e 100644
--- a/hw/scsi/scsi-disk.c
+++ b/hw/scsi/scsi-disk.c
@@ -68,6 +68,9 @@ struct SCSIDiskClass {
     /*
      * Callbacks receive ret == 0 for success. Errors are represented either as
      * negative errno values, or as positive SAM status codes.
+     *
+     * Beware: For errors returned in host_status, the function may directly
+     * complete the request and never call the callback.
      */
     DMAIOFunc       *dma_readv;
     DMAIOFunc       *dma_writev;
@@ -381,6 +384,7 @@ done:
     scsi_req_unref(&r->req);
 }
 
+/* May not be called in all error cases, don't rely on cleanup here */
 static void scsi_dma_complete(void *opaque, int ret)
 {
     SCSIDiskReq *r = (SCSIDiskReq *)opaque;
@@ -421,6 +425,7 @@ done:
     scsi_req_unref(&r->req);
 }
 
+/* May not be called in all error cases, don't rely on cleanup here */
 static void scsi_read_complete(void *opaque, int ret)
 {
     SCSIDiskReq *r = (SCSIDiskReq *)opaque;
@@ -560,6 +565,7 @@ done:
     scsi_req_unref(&r->req);
 }
 
+/* May not be called in all error cases, don't rely on cleanup here */
 static void scsi_write_complete(void * opaque, int ret)
 {
     SCSIDiskReq *r = (SCSIDiskReq *)opaque;
@@ -2821,6 +2827,7 @@ static void scsi_block_sgio_complete(void *opaque, int ret)
     sg_io_hdr_t *io_hdr = &req->io_header;
 
     if (ret == 0) {
+        /* FIXME This skips calling req->cb() and any cleanup in it */
         if (io_hdr->host_status != SCSI_HOST_OK) {
             scsi_req_complete_failed(&r->req, io_hdr->host_status);
             scsi_req_unref(&r->req);