[PATCH 13/14] passthrough/PCI: rework (s,b,d,f) init of struct pci_dev

[Jan Beulich <jbeulich@xxxxxxxx>]

Right now we're casting away const-ness, to initialize the individual
elements despite the field(s) being declared const. Eclair validly
recognizes this as a Misra rule 11.8 violation. Hide this by switching to
the use of memcpy(), deriving the destination address from the (mutable)
struct pci_dev * which we hold in hands.

No functional change intended.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Subsequently we may want to further leverage the sbdf local variable we
now have in the function. Yet of course the primary question is: Is this
an okay game to play in the first place?

--- a/xen/drivers/passthrough/pci.c
+++ b/xen/drivers/passthrough/pci.c
@@ -318,6 +318,7 @@ static void apply_quirks(struct pci_dev
 static struct pci_dev *alloc_pdev(struct pci_seg *pseg, u8 bus, u8 devfn)
 {
     struct pci_dev *pdev;
+    pci_sbdf_t sbdf = { .seg = pseg->nr, .bus = bus, .devfn = devfn };
     unsigned int pos;
     int rc;
 
@@ -329,9 +330,15 @@ static struct pci_dev *alloc_pdev(struct
     if ( !pdev )
         return NULL;
 
-    *(u16*) &pdev->seg = pseg->nr;
-    *((u8*) &pdev->bus) = bus;
-    *((u8*) &pdev->devfn) = devfn;
+    /*
+     * pdev->sbdf is deliberately const, i.e. it can't be written by structure
+     * or field assignment.  Writing by memcpy() works, as long as it's not
+     * &pdev->sbdf which is passed.  Since memcpy() isn't type-safe, have an
+     * explicit type check first.
+     */
+    (void)(&pdev->sbdf != &sbdf);
+    memcpy((void *)pdev + offsetof(struct pci_dev, sbdf), &sbdf, sizeof(sbdf));
+
     pdev->domain = NULL;
 
     INIT_LIST_HEAD(&pdev->vf_list);
@@ -390,7 +397,6 @@ static struct pci_dev *alloc_pdev(struct
                          phantom_devs[i].slot == PCI_SLOT(devfn) &&
                          phantom_devs[i].stride > PCI_FUNC(devfn) )
                     {
-                        pci_sbdf_t sbdf = pdev->sbdf;
                         unsigned int stride = phantom_devs[i].stride;
 
                         while ( (sbdf.fn += stride) > PCI_FUNC(devfn) )