error: Eliminate error_propagate() with Coccinelle, part 1

When all we do with an Error we receive into a local variable is
propagating to somewhere else, we can just as well receive it there
right away.  Convert

    if (!foo(..., &err)) {
        ...
        error_propagate(errp, err);
        ...
        return ...
    }

to

    if (!foo(..., errp)) {
        ...
        ...
        return ...
    }

where nothing else needs @err.  Coccinelle script:

    @rule1 forall@
    identifier fun, err, errp, lbl;
    expression list args, args2;
    binary operator op;
    constant c1, c2;
    symbol false;
    @@
         if (
    (
    -        fun(args, &err, args2)
    +        fun(args, errp, args2)
    |
    -        !fun(args, &err, args2)
    +        !fun(args, errp, args2)
    |
    -        fun(args, &err, args2) op c1
    +        fun(args, errp, args2) op c1
    )
            )
         {
             ... when != err
                 when != lbl:
                 when strict
    -        error_propagate(errp, err);
             ... when != err
    (
             return;
    |
             return c2;
    |
             return false;
    )
         }

    @rule2 forall@
    identifier fun, err, errp, lbl;
    expression list args, args2;
    expression var;
    binary operator op;
    constant c1, c2;
    symbol false;
    @@
    -    var = fun(args, &err, args2);
    +    var = fun(args, errp, args2);
         ... when != err
         if (
    (
             var
    |
             !var
    |
             var op c1
    )
            )
         {
             ... when != err
                 when != lbl:
                 when strict
    -        error_propagate(errp, err);
             ... when != err
    (
             return;
    |
             return c2;
    |
             return false;
    |
             return var;
    )
         }

    @depends on rule1 || rule2@
    identifier err;
    @@
    -    Error *err = NULL;
         ... when != err

Not exactly elegant, I'm afraid.

The "when != lbl:" is necessary to avoid transforming

         if (fun(args, &err)) {
             goto out
         }
         ...
     out:
         error_propagate(errp, err);

even though other paths to label out still need the error_propagate().
For an actual example, see sclp_realize().

Without the "when strict", Coccinelle transforms vfio_msix_setup(),
incorrectly.  I don't know what exactly "when strict" does, only that
it helps here.

The match of return is narrower than what I want, but I can't figure
out how to express "return where the operand doesn't use @err".  For
an example where it's too narrow, see vfio_intx_enable().

Silently fails to convert hw/arm/armsse.c, because Coccinelle gets
confused by ARMSSE being used both as typedef and function-like macro
there.  Converted manually.

Line breaks tidied up manually.  One nested declaration of @local_err
deleted manually.  Preexisting unwanted blank line dropped in
hw/riscv/sifive_e.c.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200707160613.848843-35-armbru@redhat.com>

4 files changed, 5 insertions, 14 deletions

diff --git a/hw/s390x/css.c b/hw/s390x/css.c
index ab28b2f..519dc91 100644
--- a/hw/s390x/css.c
+++ b/hw/s390x/css.c
@@ -2377,7 +2377,6 @@ static void set_css_devid(Object *obj, Visitor *v, const char *name,
     DeviceState *dev = DEVICE(obj);
     Property *prop = opaque;
     CssDevId *dev_id = qdev_get_prop_ptr(dev, prop);
-    Error *local_err = NULL;
     char *str;
     int num, n1, n2;
     unsigned int cssid, ssid, devid;
@@ -2387,8 +2386,7 @@ static void set_css_devid(Object *obj, Visitor *v, const char *name,
         return;
     }
 
-    if (!visit_type_str(v, name, &str, &local_err)) {
-        error_propagate(errp, local_err);
+    if (!visit_type_str(v, name, &str, errp)) {
         return;
     }
 
diff --git a/hw/s390x/event-facility.c b/hw/s390x/event-facility.c
index cee2908..645b408 100644
--- a/hw/s390x/event-facility.c
+++ b/hw/s390x/event-facility.c
@@ -442,16 +442,13 @@ static void init_event_facility(Object *obj)
 static void realize_event_facility(DeviceState *dev, Error **errp)
 {
     SCLPEventFacility *event_facility = EVENT_FACILITY(dev);
-    Error *local_err = NULL;
 
     if (!qdev_realize(DEVICE(&event_facility->quiesce),
-                      BUS(&event_facility->sbus), &local_err)) {
-        error_propagate(errp, local_err);
+                      BUS(&event_facility->sbus), errp)) {
         return;
     }
     if (!qdev_realize(DEVICE(&event_facility->cpu_hotplug),
-                      BUS(&event_facility->sbus), &local_err)) {
-        error_propagate(errp, local_err);
+                      BUS(&event_facility->sbus), errp)) {
         qdev_unrealize(DEVICE(&event_facility->quiesce));
         return;
     }
diff --git a/hw/s390x/virtio-ccw-crypto.c b/hw/s390x/virtio-ccw-crypto.c
index 5720e84..570c033 100644
--- a/hw/s390x/virtio-ccw-crypto.c
+++ b/hw/s390x/virtio-ccw-crypto.c
@@ -19,10 +19,8 @@ static void virtio_ccw_crypto_realize(VirtioCcwDevice *ccw_dev, Error **errp)
 {
     VirtIOCryptoCcw *dev = VIRTIO_CRYPTO_CCW(ccw_dev);
     DeviceState *vdev = DEVICE(&dev->vdev);
-    Error *err = NULL;
 
-    if (!qdev_realize(vdev, BUS(&ccw_dev->bus), &err)) {
-        error_propagate(errp, err);
+    if (!qdev_realize(vdev, BUS(&ccw_dev->bus), errp)) {
         return;
     }
 
diff --git a/hw/s390x/virtio-ccw-rng.c b/hw/s390x/virtio-ccw-rng.c
index 8cf01ce..4bb8c16 100644
--- a/hw/s390x/virtio-ccw-rng.c
+++ b/hw/s390x/virtio-ccw-rng.c
@@ -20,10 +20,8 @@ static void virtio_ccw_rng_realize(VirtioCcwDevice *ccw_dev, Error **errp)
 {
     VirtIORNGCcw *dev = VIRTIO_RNG_CCW(ccw_dev);
     DeviceState *vdev = DEVICE(&dev->vdev);
-    Error *err = NULL;
 
-    if (!qdev_realize(vdev, BUS(&ccw_dev->bus), &err)) {
-        error_propagate(errp, err);
+    if (!qdev_realize(vdev, BUS(&ccw_dev->bus), errp)) {
         return;
     }