[PATCH 06/11] hw/ide/ahci: treat a failed PRDT walk as a PIO transfer failure

["Denis V. Lunev" <den@openvz.org>]

From: Denis V. Lunev <den@openvz.org>

ahci_dma_prepare_buf() returns -1 when it cannot build a scatter-gather
list, the PRDTL of zero case among them. ahci_pio_transfer() tests the
result for truth, so a failure sets has_sglist and the transfer goes
ahead against whatever s->sg holds. AHCI 1.3.1 is explicit about the
zero case: "If this field is '0', then no data transfer shall occur
with the command."

Test for a positive byte count instead. A successful walk that yields
nothing to transfer is already handled by the size check below.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/4043
Cc: John Snow <jsnow@redhat.com>
Cc: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
---
 hw/ide/ahci.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
index 4c138b0c51..436a0eaab6 100644
--- a/hw/ide/ahci.c
+++ b/hw/ide/ahci.c
@@ -1428,7 +1428,7 @@ static bool ahci_pio_transfer(const IDEDMA *dma)
         goto out;
     }
 
-    if (ahci_dma_prepare_buf(dma, size)) {
+    if (ahci_dma_prepare_buf(dma, size) > 0) {
         has_sglist = 1;
     }
 
-- 
2.53.0