error: Fix use of error_prepend() with &error_fatal, &error_abort

From include/qapi/error.h:

  * Pass an existing error to the caller with the message modified:
  *     error_propagate(errp, err);
  *     error_prepend(errp, "Could not frobnicate '%s': ", name);

Fei Li pointed out that doing error_propagate() first doesn't work
well when @errp is &error_fatal or &error_abort: the error_prepend()
is never reached.

Since I doubt fixing the documentation will stop people from getting
it wrong, introduce error_propagate_prepend(), in the hope that it
lures people away from using its constituents in the wrong order.
Update the instructions in error.h accordingly.

Convert existing error_prepend() next to error_propagate to
error_propagate_prepend().  If any of these get reached with
&error_fatal or &error_abort, the error messages improve.  I didn't
check whether that's the case anywhere.

Cc: Fei Li <fli@suse.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20181017082702.5581-2-armbru@redhat.com>

7 files changed, 21 insertions, 20 deletions

diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
index c30f4f26bd..08e673a79c 100644
--- a/hw/9pfs/9p-local.c
+++ b/hw/9pfs/9p-local.c
@@ -1509,8 +1509,8 @@ static int local_parse_opts(QemuOpts *opts, FsDriverEntry *fse, Error **errp)
 
     fsdev_throttle_parse_opts(opts, &fse->fst, &local_err);
     if (local_err) {
-        error_propagate(errp, local_err);
-        error_prepend(errp, "invalid throttle configuration: ");
+        error_propagate_prepend(errp, local_err,
+                                "invalid throttle configuration: ");
         return -1;
     }
 
diff --git a/hw/intc/xics.c b/hw/intc/xics.c
index c90c893228..406efee064 100644
--- a/hw/intc/xics.c
+++ b/hw/intc/xics.c
@@ -320,8 +320,9 @@ static void icp_realize(DeviceState *dev, Error **errp)
 
     obj = object_property_get_link(OBJECT(dev), ICP_PROP_XICS, &err);
     if (!obj) {
-        error_propagate(errp, err);
-        error_prepend(errp, "required link '" ICP_PROP_XICS "' not found: ");
+        error_propagate_prepend(errp, err,
+                                "required link '" ICP_PROP_XICS
+                                "' not found: ");
         return;
     }
 
@@ -329,8 +330,9 @@ static void icp_realize(DeviceState *dev, Error **errp)
 
     obj = object_property_get_link(OBJECT(dev), ICP_PROP_CPU, &err);
     if (!obj) {
-        error_propagate(errp, err);
-        error_prepend(errp, "required link '" ICP_PROP_CPU "' not found: ");
+        error_propagate_prepend(errp, err,
+                                "required link '" ICP_PROP_CPU
+                                "' not found: ");
         return;
     }
 
@@ -624,8 +626,9 @@ static void ics_base_realize(DeviceState *dev, Error **errp)
 
     obj = object_property_get_link(OBJECT(dev), ICS_PROP_XICS, &err);
     if (!obj) {
-        error_propagate(errp, err);
-        error_prepend(errp, "required link '" ICS_PROP_XICS "' not found: ");
+        error_propagate_prepend(errp, err,
+                                "required link '" ICS_PROP_XICS
+                                "' not found: ");
         return;
     }
     ics->xics = XICS_FABRIC(obj);
diff --git a/hw/ppc/pnv_core.c b/hw/ppc/pnv_core.c
index 9750464bf4..ad1bcc7990 100644
--- a/hw/ppc/pnv_core.c
+++ b/hw/ppc/pnv_core.c
@@ -148,8 +148,8 @@ static void pnv_core_realize(DeviceState *dev, Error **errp)
 
     chip = object_property_get_link(OBJECT(dev), "chip", &local_err);
     if (!chip) {
-        error_propagate(errp, local_err);
-        error_prepend(errp, "required link 'chip' not found: ");
+        error_propagate_prepend(errp, local_err,
+                                "required link 'chip' not found: ");
         return;
     }
 
diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
index c2271e6ed4..58afa46204 100644
--- a/hw/ppc/spapr_pci.c
+++ b/hw/ppc/spapr_pci.c
@@ -1724,16 +1724,15 @@ static void spapr_phb_realize(DeviceState *dev, Error **errp)
         if (smc->legacy_irq_allocation) {
             irq = spapr_irq_findone(spapr, &local_err);
             if (local_err) {
-                error_propagate(errp, local_err);
-                error_prepend(errp, "can't allocate LSIs: ");
+                error_propagate_prepend(errp, local_err,
+                                        "can't allocate LSIs: ");
                 return;
             }
         }
 
         spapr_irq_claim(spapr, irq, true, &local_err);
         if (local_err) {
-            error_propagate(errp, local_err);
-            error_prepend(errp, "can't allocate LSIs: ");
+            error_propagate_prepend(errp, local_err, "can't allocate LSIs: ");
             return;
         }
 
diff --git a/hw/timer/aspeed_timer.c b/hw/timer/aspeed_timer.c
index 54b400b94a..5c786e5128 100644
--- a/hw/timer/aspeed_timer.c
+++ b/hw/timer/aspeed_timer.c
@@ -454,8 +454,7 @@ static void aspeed_timer_realize(DeviceState *dev, Error **errp)
 
     obj = object_property_get_link(OBJECT(dev), "scu", &err);
     if (!obj) {
-        error_propagate(errp, err);
-        error_prepend(errp, "required link 'scu' not found: ");
+        error_propagate_prepend(errp, err, "required link 'scu' not found: ");
         return;
     }
     s->scu = ASPEED_SCU(obj);
diff --git a/hw/usb/bus.c b/hw/usb/bus.c
index 11f7720d71..bf796d67e6 100644
--- a/hw/usb/bus.c
+++ b/hw/usb/bus.c
@@ -340,8 +340,9 @@ static USBDevice *usb_try_create_simple(USBBus *bus, const char *name,
     }
     object_property_set_bool(OBJECT(dev), true, "realized", &err);
     if (err) {
-        error_propagate(errp, err);
-        error_prepend(errp, "Failed to initialize USB device '%s': ", name);
+        error_propagate_prepend(errp, err,
+                                "Failed to initialize USB device '%s': ",
+                                name);
         return NULL;
     }
     return dev;
diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index 8b73582d51..4404c28360 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -1283,8 +1283,7 @@ static int vfio_msi_setup(VFIOPCIDevice *vdev, int pos, Error **errp)
         if (ret == -ENOTSUP) {
             return 0;
         }
-        error_prepend(&err, "msi_init failed: ");
-        error_propagate(errp, err);
+        error_propagate_prepend(errp, err, "msi_init failed: ");
         return ret;
     }
     vdev->msi_cap_size = 0xa + (msi_maskbit ? 0xa : 0) + (msi_64bit ? 0x4 : 0);