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>

1 files changed, 3 insertions, 6 deletions

diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c
index 1f18b79348..43d12bc33a 100644
--- a/hw/ppc/spapr_drc.c
+++ b/hw/ppc/spapr_drc.c
@@ -327,8 +327,7 @@ static void prop_get_fdt(Object *obj, Visitor *v, const char *name,
         case FDT_BEGIN_NODE:
             fdt_depth++;
             name = fdt_get_name(fdt, fdt_offset, &name_len);
-            if (!visit_start_struct(v, name, NULL, 0, &err)) {
-                error_propagate(errp, err);
+            if (!visit_start_struct(v, name, NULL, 0, errp)) {
                 return;
             }
             break;
@@ -347,14 +346,12 @@ static void prop_get_fdt(Object *obj, Visitor *v, const char *name,
             int i;
             prop = fdt_get_property_by_offset(fdt, fdt_offset, &prop_len);
             name = fdt_string(fdt, fdt32_to_cpu(prop->nameoff));
-            if (!visit_start_list(v, name, NULL, 0, &err)) {
-                error_propagate(errp, err);
+            if (!visit_start_list(v, name, NULL, 0, errp)) {
                 return;
             }
             for (i = 0; i < prop_len; i++) {
                 if (!visit_type_uint8(v, NULL, (uint8_t *)&prop->data[i],
-                                      &err)) {
-                    error_propagate(errp, err);
+                                      errp)) {
                     return;
                 }
             }