From 668f62ec621e4e2919fb7d4caa5d805764c5852d Mon Sep 17 00:00:00 2001
From: Markus Armbruster
Date: Tue, 7 Jul 2020 18:06:02 +0200
Subject: 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>
---
 backends/hostmem-file.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

(limited to 'backends/hostmem-file.c')

diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
index a44f5a61ac..5b819020b4 100644
--- a/backends/hostmem-file.c
+++ b/backends/hostmem-file.c
@@ -110,7 +110,6 @@ static void file_memory_backend_set_align(Object *o, Visitor *v,
 {
     HostMemoryBackend *backend = MEMORY_BACKEND(o);
     HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
-    Error *local_err = NULL;
     uint64_t val;
 
     if (host_memory_backend_mr_inited(backend)) {
@@ -119,8 +118,7 @@ static void file_memory_backend_set_align(Object *o, Visitor *v,
         return;
     }
 
-    if (!visit_type_size(v, name, &val, &local_err)) {
-        error_propagate(errp, local_err);
+    if (!visit_type_size(v, name, &val, errp)) {
         return;
     }
     fb->align = val;
-- 
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