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>

2 files changed, 3 insertions, 8 deletions

diff --git a/hw/vfio/pci-quirks.c b/hw/vfio/pci-quirks.c
index 1467b80..3a14b7c 100644
--- a/hw/vfio/pci-quirks.c
+++ b/hw/vfio/pci-quirks.c
@@ -1502,15 +1502,13 @@ static void set_nv_gpudirect_clique_id(Object *obj, Visitor *v,
     DeviceState *dev = DEVICE(obj);
     Property *prop = opaque;
     uint8_t value, *ptr = qdev_get_prop_ptr(dev, prop);
-    Error *local_err = NULL;
 
     if (dev->realized) {
         qdev_prop_set_after_realize(dev, name, errp);
         return;
     }
 
-    if (!visit_type_uint8(v, name, &value, &local_err)) {
-        error_propagate(errp, local_err);
+    if (!visit_type_uint8(v, name, &value, errp)) {
         return;
     }
 
diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index d020ea9..6fde80c 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -116,7 +116,6 @@ static void vfio_intx_enable_kvm(VFIOPCIDevice *vdev, Error **errp)
 {
 #ifdef CONFIG_KVM
     int irq_fd = event_notifier_get_fd(&vdev->intx.interrupt);
-    Error *err = NULL;
 
     if (vdev->no_kvm_intx || !kvm_irqfds_enabled() ||
         vdev->intx.route.mode != PCI_INTX_ENABLED ||
@@ -147,8 +146,7 @@ static void vfio_intx_enable_kvm(VFIOPCIDevice *vdev, Error **errp)
     if (vfio_set_irq_signaling(&vdev->vbasedev, VFIO_PCI_INTX_IRQ_INDEX, 0,
                                VFIO_IRQ_SET_ACTION_UNMASK,
                                event_notifier_get_fd(&vdev->intx.unmask),
-                               &err)) {
-        error_propagate(errp, err);
+                               errp)) {
         goto fail_vfio;
     }
 
@@ -2741,9 +2739,8 @@ static void vfio_realize(PCIDevice *pdev, Error **errp)
     if (!pdev->failover_pair_id) {
         error_setg(&vdev->migration_blocker,
                 "VFIO device doesn't support migration");
-        ret = migrate_add_blocker(vdev->migration_blocker, &err);
+        ret = migrate_add_blocker(vdev->migration_blocker, errp);
         if (ret) {
-            error_propagate(errp, err);
             error_free(vdev->migration_blocker);
             vdev->migration_blocker = NULL;
             return;