[PATCH 5/5] vPCI/MSI-X: tidy init_msix()

[Jan Beulich <jbeulich@xxxxxxxx>]

First of all introduce a local variable for the to be allocated struct.
The compiler can't CSE all the occurrences (I'm observing 80 bytes of
code saved with gcc 10). Additionally, while the caller can cope and
there was no memory leak, globally "announce" the struct only once done
initializing it. This also removes the dependency of the function on
the caller cleaning up after it in case of an error.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
I was heavily tempted to also move up the call to vpci_add_register(),
such that there would be no pointless init done in case of an error
coming back from there.

--- a/xen/drivers/vpci/msix.c
+++ b/xen/drivers/vpci/msix.c
@@ -436,6 +436,7 @@ static int init_msix(struct pci_dev *pde
     uint8_t slot = PCI_SLOT(pdev->devfn), func = PCI_FUNC(pdev->devfn);
     unsigned int msix_offset, i, max_entries;
     uint16_t control;
+    struct vpci_msix *msix;
     int rc;
 
     msix_offset = pci_find_cap_offset(pdev->seg, pdev->bus, slot, func,
@@ -447,34 +448,37 @@ static int init_msix(struct pci_dev *pde
 
     max_entries = msix_table_size(control);
 
-    pdev->vpci->msix = xzalloc_flex_struct(struct vpci_msix, entries,
-                                           max_entries);
-    if ( !pdev->vpci->msix )
+    msix = xzalloc_flex_struct(struct vpci_msix, entries, max_entries);
+    if ( !msix )
         return -ENOMEM;
 
-    pdev->vpci->msix->max_entries = max_entries;
-    pdev->vpci->msix->pdev = pdev;
+    msix->max_entries = max_entries;
+    msix->pdev = pdev;
 
-    pdev->vpci->msix->tables[VPCI_MSIX_TABLE] =
+    msix->tables[VPCI_MSIX_TABLE] =
         pci_conf_read32(pdev->sbdf, msix_table_offset_reg(msix_offset));
-    pdev->vpci->msix->tables[VPCI_MSIX_PBA] =
+    msix->tables[VPCI_MSIX_PBA] =
         pci_conf_read32(pdev->sbdf, msix_pba_offset_reg(msix_offset));
 
-    for ( i = 0; i < pdev->vpci->msix->max_entries; i++)
+    for ( i = 0; i < msix->max_entries; i++)
     {
-        pdev->vpci->msix->entries[i].masked = true;
-        vpci_msix_arch_init_entry(&pdev->vpci->msix->entries[i]);
+        msix->entries[i].masked = true;
+        vpci_msix_arch_init_entry(&msix->entries[i]);
     }
 
     rc = vpci_add_register(pdev->vpci, control_read, control_write,
-                           msix_control_reg(msix_offset), 2, pdev->vpci->msix);
+                           msix_control_reg(msix_offset), 2, msix);
     if ( rc )
+    {
+        xfree(msix);
         return rc;
+    }
 
     if ( list_empty(&d->arch.hvm.msix_tables) )
         register_mmio_handler(d, &vpci_msix_table_ops);
 
-    list_add(&pdev->vpci->msix->next, &d->arch.hvm.msix_tables);
+    pdev->vpci->msix = msix;
+    list_add(&msix->next, &d->arch.hvm.msix_tables);
 
     return 0;
 }