On Fri, Jan 05, 2024 at 03:20:16 -0500, Laine Stump wrote:
Rather than always binding to the vfio-pci driver, use the new function virPCIDeviceFindBestVFIOVariant() to see if the running kernel has a VFIO variant driver available that is a better match for the device, and if one is found, use that instead.
virPCIDeviceFindBestVFIOVariant() function reads the modalias file for the given device from sysfs, then looks through /lib/modules/${kernel_release}/modules.alias for the vfio_pci alias that matches with the least number of wildcard ('*') fields.
The appropriate "VFIO variant" driver for a device will be the PCI driver implemented by the discovered module - these drivers are compatible with (and provide the entire API of) the standard vfio-pci driver, but have additional device-specific APIs that can be useful for, e.g., saving/restoring state for migration.
If a specific driver is named (using <driver model='blah'/> in the device XML), that will still be used rather than searching modules.alias; this makes it possible to force binding of vfio-pci if there is an issue with the auto-selected variant driver.
Signed-off-by: Laine Stump <laine@redhat.com> ---
Changes from V2:
* fail if device modalias file isn't found.
This [1] ...
* use unsigned int instead of int for wildcardCt * increase file memory buffer from 4MB to 8MB * other minor nits pointed out by Peter
[...]
+/* virPCIDeviceFindBestVFIOVariant: + * + * Find the "best" match of all vfio_pci aliases for @dev in the host + * modules.alias file. This uses the algorithm of finding every + * modules.alias line that begins with "vfio_pci:", then picking the + * one that matches the device's own modalias value (from the file of + * that name in the device's sysfs directory) with the fewest + * "wildcards" (* character, meaning "match any value for this + * attribute"). + */ +int +virPCIDeviceFindBestVFIOVariant(virPCIDevice *dev, + char **moduleName) +{ + g_autofree char *devModAliasPath = NULL; + g_autofree char *devModAliasContent = NULL; + const char *devModAlias; + g_autoptr(virPCIDeviceAliasInfo) devModAliasInfo = NULL; + struct utsname unameInfo; + g_autofree char *modulesAliasPath = NULL; + g_autofree char *modulesAliasContent = NULL; + const char *line; + unsigned int currentBestWildcardCt = INT_MAX;
UINT_MAX
+ + *moduleName = NULL; + + /* get the modalias values for the device from sysfs */ + devModAliasPath = virPCIFile(dev->name, "modalias"); + if (virFileReadAll(devModAliasPath, 100, &devModAliasContent) < 0)
... [1] isn't true.
+ return -1; + + VIR_DEBUG("modalias path: '%s' contents: '%s'", + devModAliasPath, devModAliasContent); + + /* "pci:vNNNNNNNNdNNNNNNNNsvNNNNNNNNsdNNNNNNNNbcNNscNNiNN\n" */ + if ((devModAlias = STRSKIP(devModAliasContent, "pci:")) == NULL || + !(devModAliasInfo = virPCIDeviceAliasInfoNew(devModAlias))) { + virReportError(VIR_ERR_INTERNAL_ERROR, + _("device modalias file %1$s content has improper format"), + devModAliasPath); + return -1; + } + + uname(&unameInfo); + modulesAliasPath = g_strdup_printf("/lib/modules/%s/modules.alias", unameInfo.release); + if (virFileReadAll(modulesAliasPath, 8 * 1024 * 1024, &modulesAliasContent) < 0) + return -1;
IIUC this is picking a driver which is 'better' than the default 'vfio_pci', but the device itself would still work if the default were used, right? In such case do we really want to treat any of the errors above as failures? I presueme a workaround for if any of the above breaks is to use an explicitly specified driver, right?
+ + /* Look for all lines that are aliases for vfio_pci drivers. + * (The first line is always a comment, so we can be sure "alias" + * is preceded by a newline) + */ + line = modulesAliasContent; +