[RFC XEN PATCH v6 4/5] libxl: Use gsi instead of irq for mapping pirq

[Jiqian Chen <Jiqian.Chen@xxxxxxx>]

In PVH dom0, it uses the linux local interrupt mechanism,
when it allocs irq for a gsi, it is dynamic, and follow
the principle of applying first, distributing first. And
the irq number is alloced from small to large, but the
applying gsi number is not, may gsi 38 comes before gsi
28, that causes the irq number is not equal with the gsi
number. And when passthrough a device, xl wants to use
gsi to map pirq, see pci_add_dm_done->xc_physdev_map_pirq,
but the gsi number is got from file
/sys/bus/pci/devices/<sbdf>/irq in current code, so it
will fail when mapping.

So, use real gsi number read from gsi sysfs.

Signed-off-by: Huang Rui <ray.huang@xxxxxxx>
Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

---
RFC: discussions ongoing on the Linux side where/how to expose the gsi

---
 tools/libs/light/libxl_pci.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/tools/libs/light/libxl_pci.c b/tools/libs/light/libxl_pci.c
index 96cb4da0794e..2cec83e0b734 100644
--- a/tools/libs/light/libxl_pci.c
+++ b/tools/libs/light/libxl_pci.c
@@ -1478,8 +1478,14 @@ static void pci_add_dm_done(libxl__egc *egc,
     fclose(f);
     if (!pci_supp_legacy_irq())
         goto out_no_irq;
-    sysfs_path = GCSPRINTF(SYSFS_PCI_DEV"/"PCI_BDF"/irq", pci->domain,
+    sysfs_path = GCSPRINTF(SYSFS_PCI_DEV"/"PCI_BDF"/gsi", pci->domain,
                                 pci->bus, pci->dev, pci->func);
+    r = access(sysfs_path, F_OK);
+    if (r && errno == ENOENT) {
+        /* To compitable with old version of kernel, still need to use irq */
+        sysfs_path = GCSPRINTF(SYSFS_PCI_DEV"/"PCI_BDF"/irq", pci->domain,
+                               pci->bus, pci->dev, pci->func);
+    }
     f = fopen(sysfs_path, "r");
     if (f == NULL) {
         LOGED(ERROR, domainid, "Couldn't open %s", sysfs_path);
@@ -2229,9 +2235,15 @@ skip_bar:
     if (!pci_supp_legacy_irq())
         goto skip_legacy_irq;
 
-    sysfs_path = GCSPRINTF(SYSFS_PCI_DEV"/"PCI_BDF"/irq", pci->domain,
+    sysfs_path = GCSPRINTF(SYSFS_PCI_DEV"/"PCI_BDF"/gsi", pci->domain,
                            pci->bus, pci->dev, pci->func);
 
+    rc = access(sysfs_path, F_OK);
+    if (rc && errno == ENOENT) {
+        /* To compitable with old version of kernel, still need to use irq */
+        sysfs_path = GCSPRINTF(SYSFS_PCI_DEV"/"PCI_BDF"/irq", pci->domain,
+                               pci->bus, pci->dev, pci->func);
+    }
     f = fopen(sysfs_path, "r");
     if (f == NULL) {
         LOGED(ERROR, domid, "Couldn't open %s", sysfs_path);
-- 
2.34.1