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>

3 files changed, 4 insertions, 12 deletions

diff --git a/hw/char/serial-pci-multi.c b/hw/char/serial-pci-multi.c
index 1328967461..2cf3e44177 100644
--- a/hw/char/serial-pci-multi.c
+++ b/hw/char/serial-pci-multi.c
@@ -95,7 +95,6 @@ static void multi_serial_pci_realize(PCIDevice *dev, Error **errp)
     PCIDeviceClass *pc = PCI_DEVICE_GET_CLASS(dev);
     PCIMultiSerialState *pci = DO_UPCAST(PCIMultiSerialState, dev, dev);
     SerialState *s;
-    Error *err = NULL;
     size_t i, nports = multi_serial_get_port_count(pc);
 
     pci->dev.config[PCI_CLASS_PROG] = pci->prog_if;
@@ -106,8 +105,7 @@ static void multi_serial_pci_realize(PCIDevice *dev, Error **errp)
 
     for (i = 0; i < nports; i++) {
         s = pci->state + i;
-        if (!qdev_realize(DEVICE(s), NULL, &err)) {
-            error_propagate(errp, err);
+        if (!qdev_realize(DEVICE(s), NULL, errp)) {
             multi_serial_pci_exit(dev);
             return;
         }
diff --git a/hw/char/serial-pci.c b/hw/char/serial-pci.c
index d22617426b..cd56924a43 100644
--- a/hw/char/serial-pci.c
+++ b/hw/char/serial-pci.c
@@ -47,10 +47,8 @@ static void serial_pci_realize(PCIDevice *dev, Error **errp)
 {
     PCISerialState *pci = DO_UPCAST(PCISerialState, dev, dev);
     SerialState *s = &pci->state;
-    Error *err = NULL;
 
-    if (!qdev_realize(DEVICE(s), NULL, &err)) {
-        error_propagate(errp, err);
+    if (!qdev_realize(DEVICE(s), NULL, errp)) {
         return;
     }
 
diff --git a/hw/char/serial.c b/hw/char/serial.c
index e69096eace..2386479492 100644
--- a/hw/char/serial.c
+++ b/hw/char/serial.c
@@ -989,10 +989,8 @@ static void serial_io_realize(DeviceState *dev, Error **errp)
 {
     SerialIO *sio = SERIAL_IO(dev);
     SerialState *s = &sio->serial;
-    Error *local_err = NULL;
 
-    if (!qdev_realize(DEVICE(s), NULL, &local_err)) {
-        error_propagate(errp, local_err);
+    if (!qdev_realize(DEVICE(s), NULL, errp)) {
         return;
     }
 
@@ -1095,10 +1093,8 @@ static void serial_mm_realize(DeviceState *dev, Error **errp)
 {
     SerialMM *smm = SERIAL_MM(dev);
     SerialState *s = &smm->serial;
-    Error *local_err = NULL;
 
-    if (!qdev_realize(DEVICE(s), NULL, &local_err)) {
-        error_propagate(errp, local_err);
+    if (!qdev_realize(DEVICE(s), NULL, errp)) {
         return;
     }