drive_get_next() is basically a bad idea.  It returns the "next" block
backend of a certain interface type.  "Next" means bus=0,unit=N, where
subsequent calls count N up from zero, per interface type.

This lets you define unit numbers implicitly by execution order.  If the
order changes, or new calls appear "in the middle", unit numbers change.
ABI break.  Hard to spot in review.

Machine "mcimx7d-sabre" connects backends with drive_get_next() in a
counting loop.  Change it to use drive_get() directly.  This makes the
unit numbers explicit in the code.

Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Andrey Smirnov <andrew.smirnov@gmail.com>
Cc: qemu-arm@nongnu.org
Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 hw/arm/mcimx7d-sabre.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/arm/mcimx7d-sabre.c b/hw/arm/mcimx7d-sabre.c
index 935d4b0f1c..50a5ecde31 100644
--- a/hw/arm/mcimx7d-sabre.c
+++ b/hw/arm/mcimx7d-sabre.c
@@ -52,7 +52,7 @@ static void mcimx7d_sabre_init(MachineState *machine)
         DriveInfo *di;
         BlockBackend *blk;
 
-        di = drive_get_next(IF_SD);
+        di = drive_get(IF_SD, 0, i);
         blk = di ? blk_by_legacy_dinfo(di) : NULL;
         bus = qdev_get_child_bus(DEVICE(&s->usdhc[i]), "sd-bus");
         carddev = qdev_new(TYPE_SD_CARD);
-- 
2.31.1

On Wed, 17 Nov 2021 at 16:34, Markus Armbruster <armbru@redhat.com> wrote:
>
> drive_get_next() is basically a bad idea.  It returns the "next" block
> backend of a certain interface type.  "Next" means bus=0,unit=N, where
> subsequent calls count N up from zero, per interface type.
>
> This lets you define unit numbers implicitly by execution order.  If the
> order changes, or new calls appear "in the middle", unit numbers change.
> ABI break.  Hard to spot in review.
>
> Machine "mcimx7d-sabre" connects backends with drive_get_next() in a
> counting loop.  Change it to use drive_get() directly.  This makes the
> unit numbers explicit in the code.
>
> Cc: Peter Maydell <peter.maydell@linaro.org>
> Cc: Andrey Smirnov <andrew.smirnov@gmail.com>
> Cc: qemu-arm@nongnu.org
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM