libxl: support reset file on sysfs

Recent kernels have a reset file on sysfs per PCI device, to allow PCI
device reset from userspace.
This patch adds support to libxl for resetting PCI devices using the
reset file on sysfs, in case the do_flr file is not preset.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

tools/libxl/libxl.c

@@ -2381,7 +2381,7 @@ int libxl_device_pci_add(struct libxl_ctx *ctx, uint32_t domid, libxl_device_pci
 
     /* TODO: check if the device can be assigned */
 
-    libxl_device_pci_flr(ctx, pcidev->domain, pcidev->bus, pcidev->dev, pcidev->func);
+    libxl_device_pci_reset(ctx, pcidev->domain, pcidev->bus, pcidev->dev, pcidev->func);
 
     stubdomid = libxl_get_stubdom_id(ctx, domid);
     if (stubdomid != 0) {
@@ -2551,7 +2551,7 @@ skip1:
         fclose(f);
     }
 out:
-    libxl_device_pci_flr(ctx, pcidev->domain, pcidev->bus, pcidev->dev, pcidev->func);
+    libxl_device_pci_reset(ctx, pcidev->domain, pcidev->bus, pcidev->dev, pcidev->func);
 
     if (!libxl_is_stubdom(ctx, domid, NULL)) {
         rc = xc_deassign_device(ctx->xch, domid, pcidev->value);

tools/libxl/libxl_device.c

@@ -22,6 +22,8 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>
+#include <fcntl.h>
+
 
 #include "libxl.h"
 #include "libxl_internal.h"
@@ -389,22 +391,36 @@ int libxl_device_del(struct libxl_ctx *ctx, libxl_device *dev, int wait)
     return 0;
 }
 
-int libxl_device_pci_flr(struct libxl_ctx *ctx, unsigned int domain, unsigned int bus,
+int libxl_device_pci_reset(struct libxl_ctx *ctx, unsigned int domain, unsigned int bus,
                          unsigned int dev, unsigned int func)
 {
-    char *do_flr = "/sys/bus/pci/drivers/pciback/do_flr";
-    FILE *fd;
+    char *reset = "/sys/bus/pci/drivers/pciback/do_flr";
+    int fd, rc;
 
-    fd = fopen(do_flr, "w");
-    if (fd != NULL) {
-        fprintf(fd, PCI_BDF, domain, bus, dev, func);
-        fclose(fd);
-        return 0;
+    fd = open(reset, O_WRONLY);
+    if (fd > 0) {
+        char *buf = libxl_sprintf(ctx, PCI_BDF, domain, bus, dev, func);
+        rc = write(fd, buf, strlen(buf));
+        if (rc < 0)
+            XL_LOG(ctx, XL_LOG_ERROR, "write to %s returned %d", reset, rc);
+        close(fd);
+        return rc < 0 ? rc : 0;
+    }
+    if (errno != ENOENT)
+        XL_LOG_ERRNO(ctx, XL_LOG_ERROR, "Failed to access pciback path %s", reset);
+    reset = libxl_sprintf(ctx, "/sys/bus/pci/devices/"PCI_BDF"/reset", domain, bus, dev, func);
+    fd = open(reset, O_WRONLY);
+    if (fd > 0) {
+        rc = write(fd, "1", 1);
+        if (rc < 0)
+            XL_LOG_ERRNO(ctx, XL_LOG_ERROR, "write to %s returned %d", reset, rc);
+        close(fd);
+        return rc < 0 ? rc : 0;
     }
     if (errno == ENOENT) {
-        XL_LOG(ctx, XL_LOG_ERROR, "Pciback doesn't support do_flr, cannot flr the device");
+        XL_LOG(ctx, XL_LOG_ERROR, "The kernel doesn't support PCI device reset from sysfs");
     } else {
-        XL_LOG_ERRNO(ctx, XL_LOG_ERROR, "Failed to access pciback path %s", do_flr);
+        XL_LOG_ERRNO(ctx, XL_LOG_ERROR, "Failed to access reset path %s", reset);
     }
     return -1;
 }

tools/libxl/libxl_internal.h

@@ -162,8 +162,8 @@ int libxl_wait_for_device_model(struct libxl_ctx *ctx,
                                                       void *userdata),
                                 void *check_callback_userdata);
 int libxl_wait_for_backend(struct libxl_ctx *ctx, char *be_path, char *state);
-int libxl_device_pci_flr(struct libxl_ctx *ctx, unsigned int domain, unsigned int bus,
-                         unsigned int dev, unsigned int func);
+int libxl_device_pci_reset(struct libxl_ctx *ctx, unsigned int domain, unsigned int bus,
+                           unsigned int dev, unsigned int func);
 
 /* from xenguest (helper */
 int hvm_build_set_params(xc_interface *handle, uint32_t domid,