s390x/pci: Add routine to get the vfio dma available count

Create new files for separating out vfio-specific work for s390
pci. Add the first such routine, which issues VFIO_IOMMU_GET_INFO
ioctl to collect the current dma available count.

Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
[aw: Fix non-Linux build with CONFIG_LINUX]
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

hw/s390x/meson.build

@@ -27,6 +27,7 @@ s390x_ss.add(when: 'CONFIG_KVM', if_true: files(
 ))
 s390x_ss.add(when: 'CONFIG_S390_CCW_VIRTIO', if_true: files('s390-virtio-ccw.c'))
 s390x_ss.add(when: 'CONFIG_TERMINAL3270', if_true: files('3270-ccw.c'))
+s390x_ss.add(when: 'CONFIG_LINUX', if_true: files('s390-pci-vfio.c'))
 
 virtio_ss = ss.source_set()
 virtio_ss.add(files('virtio-ccw.c'))

hw/s390x/s390-pci-vfio.c

@@ -0,0 +1,54 @@
+/*
+ * s390 vfio-pci interfaces
+ *
+ * Copyright 2020 IBM Corp.
+ * Author(s): Matthew Rosato <mjrosato@linux.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or (at
+ * your option) any later version. See the COPYING file in the top-level
+ * directory.
+ */
+
+#include <sys/ioctl.h>
+
+#include "qemu/osdep.h"
+#include "hw/s390x/s390-pci-vfio.h"
+#include "hw/vfio/vfio-common.h"
+
+/*
+ * Get the current DMA available count from vfio.  Returns true if vfio is
+ * limiting DMA requests, false otherwise.  The current available count read
+ * from vfio is returned in avail.
+ */
+bool s390_pci_update_dma_avail(int fd, unsigned int *avail)
+{
+    g_autofree struct vfio_iommu_type1_info *info;
+    uint32_t argsz;
+
+    assert(avail);
+
+    argsz = sizeof(struct vfio_iommu_type1_info);
+    info = g_malloc0(argsz);
+
+    /*
+     * If the specified argsz is not large enough to contain all capabilities
+     * it will be updated upon return from the ioctl.  Retry until we have
+     * a big enough buffer to hold the entire capability chain.
+     */
+retry:
+    info->argsz = argsz;
+
+    if (ioctl(fd, VFIO_IOMMU_GET_INFO, info)) {
+        return false;
+    }
+
+    if (info->argsz > argsz) {
+        argsz = info->argsz;
+        info = g_realloc(info, argsz);
+        goto retry;
+    }
+
+    /* If the capability exists, update with the current value */
+    return vfio_get_info_dma_avail(info, avail);
+}
+

include/hw/s390x/s390-pci-vfio.h

@@ -0,0 +1,24 @@
+/*
+ * s390 vfio-pci interfaces
+ *
+ * Copyright 2020 IBM Corp.
+ * Author(s): Matthew Rosato <mjrosato@linux.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or (at
+ * your option) any later version. See the COPYING file in the top-level
+ * directory.
+ */
+
+#ifndef HW_S390_PCI_VFIO_H
+#define HW_S390_PCI_VFIO_H
+
+#ifdef CONFIG_LINUX
+bool s390_pci_update_dma_avail(int fd, unsigned int *avail);
+#else
+static inline bool s390_pci_update_dma_avail(int fd, unsigned int *avail)
+{
+    return false;
+}
+#endif
+
+#endif