pci_add_capability appears most PCI devices. Its error handling required
lots of code, and led to inconsistent behaviors such as:
- passing error_abort
- passing error_fatal
- asserting the returned value
- propagating the error to the caller
- skipping the rest of the function
- just ignoring

The code generating errors in pci_add_capability had a comment which
says:
> Verify that capabilities don't overlap.  Note: device assignment
> depends on this check to verify that the device is not broken.
> Should never trigger for emulated devices, but it's helpful for
> debugging these.

Indeed vfio has some code that passes capability offsets and sizes from
a physical device, but it explicitly pays attention so that the
capabilities never overlap. Therefore, we can always assert that
capabilities never overlap when pci_add_capability is called, resolving
these inconsistencies.

Such an implementation of pci_add_capability will not have errp
parameter. However, there are so many callers of pci_add_capability
that it does not make sense to amend all of them at once to match
with the new signature. Instead, this change will allow callers of
pci_add_capability to omit errp as the first step.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
---
 hw/pci/pci.c         |  8 ++++----
 include/hw/pci/pci.h | 13 ++++++++++---
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index 33f5406706..9e62c8e75d 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -2530,14 +2530,14 @@ void pci_check_capability_overlap(PCIDevice *pdev, uint8_t cap_id,
 }
 
 /*
- * On success, pci_add_capability() returns a positive value
+ * On success, pci_add_capability_legacy() returns a positive value
  * that the offset of the pci capability.
  * On failure, it sets an error and returns a negative error
  * code.
  */
-int pci_add_capability(PCIDevice *pdev, uint8_t cap_id,
-                       uint8_t offset, uint8_t size,
-                       Error **errp)
+int pci_add_capability_legacy(PCIDevice *pdev, uint8_t cap_id,
+                              uint8_t offset, uint8_t size,
+                              Error **errp)
 {
     uint8_t *config;
 
diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
index 75e64ecdf2..4f3e1e2558 100644
--- a/include/hw/pci/pci.h
+++ b/include/hw/pci/pci.h
@@ -2,6 +2,7 @@
 #define QEMU_PCI_H
 
 #include "exec/memory.h"
+#include "qapi/error.h"
 #include "sysemu/dma.h"
 
 /* PCI includes legacy ISA access.  */
@@ -393,9 +394,15 @@ pcibus_t pci_get_bar_addr(PCIDevice *pci_dev, int region_num);
 void pci_check_capability_overlap(PCIDevice *pdev, uint8_t cap_id,
                                   uint8_t offset, uint8_t size, Error **errp);
 
-int pci_add_capability(PCIDevice *pdev, uint8_t cap_id,
-                       uint8_t offset, uint8_t size,
-                       Error **errp);
+int pci_add_capability_legacy(PCIDevice *pdev, uint8_t cap_id,
+                              uint8_t offset, uint8_t size,
+                              Error **errp);
+
+#define PCI_ADD_CAPABILITY_VA(pdev, cap_id, offset, size, errp, ...) \
+    pci_add_capability_legacy(pdev, cap_id, offset, size, errp)
+
+#define pci_add_capability(...) \
+    PCI_ADD_CAPABILITY_VA(__VA_ARGS__, &error_abort)
 
 void pci_del_capability(PCIDevice *pci_dev, uint8_t cap_id, uint8_t cap_size);
 
-- 
2.38.1