Re: [libvirt] [PATCH 3/3] nodedev: Work around the uevent race by hooking up virFileWaitForAccess

If we find ourselves in the situation that the 'add' uevent has been fired earlier than the sysfs tree for a device, we'd better wait for the attributes to be ready rather than discarding the device from our device list forever.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1463285 Signed-off-by: Erik Skultety <eskultet(a)redhat.com&gt; --- src/node_device/node_device_udev.c | 48 +++++++++++++++++++++++++++++++++++++- 1 file changed, 47 insertions(+), 1 deletion(-) diff --git a/src/node_device/node_device_udev.c b/src/node_device/node_device_udev.c index 174124a1b..4f9ca0c67 100644 --- a/src/node_device/node_device_udev.c +++ b/src/node_device/node_device_udev.c @@ -60,6 +60,43 @@ struct _udevPrivate { }; +/** + * udevWaitForAttrs: + * @sys_path: node device base path + * @...: attributes to wait for, last attribute must be NULL + * + * Takes a list of attributes to wait for, waits until all of them are + * available, unless the max number of tries (10) has been reached. + * + * Returns 0 if all attributes became available, -1 on error.

+ */ +static int +udevWaitForAttrs(const char *sys_path, ...) +{ + int ret = -1; + const char *attr = NULL; + char *attr_path = NULL; + va_list args; + + va_start(args, sys_path); + while ((attr = va_arg(args, char *))) { + if (virAsprintf(&attr_path, "%s/%s", sys_path, attr) < 0) + goto cleanup; + + if (virFileWaitForAccess(attr_path, 100, 10) < 0)

+ goto cleanup; + + VIR_FREE(attr_path); + } + + ret = 0; + cleanup: + va_end(args); + VIR_FREE(attr_path); + return ret; +} + + static bool udevHasDeviceProperty(struct udev_device *dev, const char *key) @@ -1113,12 +1150,21 @@ udevProcessMediatedDevice(struct udev_device *dev, { int ret = -1; const char *uuidstr = NULL; + const char *devpath = udev_device_get_syspath(dev); int iommugrp = -1; char *linkpath = NULL; char *canonicalpath = NULL; virNodeDevCapMdevPtr data = &def->caps->data.mdev; - if (virAsprintf(&linkpath, "%s/mdev_type", udev_device_get_syspath(dev)) < 0) + /* Because of a kernel uevent race, we might get the 'add' event prior to + * the sysfs tree being ready, so any attempt to access any sysfs attribute + * would result in ENOENT and us dropping the device, so let's work around + * it by waiting for the attributes to become available. + */ + if (udevWaitForAttrs(devpath, "mdev_type", "iommu_group", NULL) < 0) + goto cleanup;

+ + if (virAsprintf(&linkpath, "%s/mdev_type", devpath) < 0) goto cleanup;