[libvirt PATCH 14/15] util: new function virPCIDeviceFindBestVFIOVariant()
Laine Stump
laine at redhat.com
Mon Oct 23 04:54:50 UTC 2023
This 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.
This can be used to find an appropriate "VFIO variant" driver for a
device (it 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.
Signed-off-by: Laine Stump <laine at redhat.com>
---
src/util/virpci.c | 224 ++++++++++++++++++++++++++++++++++++++++++++++
src/util/virpci.h | 2 +
2 files changed, 226 insertions(+)
diff --git a/src/util/virpci.c b/src/util/virpci.c
index 513ae948c0..70fcedc4a5 100644
--- a/src/util/virpci.c
+++ b/src/util/virpci.c
@@ -30,6 +30,10 @@
#include <sys/stat.h>
#include <unistd.h>
+#ifndef WIN32
+# include <sys/utsname.h>
+#endif
+
#include "virlog.h"
#include "virerror.h"
#include "virfile.h"
@@ -1539,6 +1543,226 @@ virPCIDeviceReattach(virPCIDevice *dev,
return 0;
}
+
+#ifndef WIN32
+typedef struct {
+ /* this is the decomposed version of a string like:
+ *
+ * vNNNNNNNNdNNNNNNNNsvNNNNNNNNsdNNNNNNNNbcNNscNNiNN
+ *
+ * (followed by a space or newline). The "NNNN" are always of the
+ * length in the example unless replaced with a wildcard ("*"),
+ * but we make no assumptions about length.
+ *
+ * Rather than name each field, we just put them
+ * all in an array of 6 elements, so that we
+ * can write a simple loop to compare them
+ */
+ char *fields[7]; /* v, d, sv, sd, bc, sc, i */
+} virPCIDeviceAliasInfo;
+
+
+/* NULL in last position makes parsing loop simpler */
+static const char *fieldnames[] = { "v", "d", "sv", "sd", "bc", "sc", "i", NULL };
+
+
+static void
+virPCIDeviceAliasInfoFree(virPCIDeviceAliasInfo *info)
+{
+ if (info) {
+ size_t i;
+
+ for (i = 0; i < G_N_ELEMENTS(info->fields); i++)
+ g_free(info->fields[i]);
+
+ g_free(info);
+ }
+}
+
+G_DEFINE_AUTOPTR_CLEANUP_FUNC(virPCIDeviceAliasInfo, virPCIDeviceAliasInfoFree);
+
+
+static virPCIDeviceAliasInfo *
+virPCIDeviceAliasInfoNew(const char *str)
+{
+ const char *field = str;
+
+ size_t i;
+ g_autoptr(virPCIDeviceAliasInfo) ret = g_new0(virPCIDeviceAliasInfo, 1);
+
+ if (!str)
+ return g_steal_pointer(&ret);
+
+ /* initialize from str */
+ for (i = 0; i < G_N_ELEMENTS(ret->fields); i++) {
+ int len = strlen(fieldnames[i]);
+ const char *next;
+
+ if (strncmp(field, fieldnames[i], len))
+ return NULL;
+
+ field += len;
+ if (fieldnames[i + 1]) {
+ if (!(next = strstr(field, fieldnames[i + 1])))
+ return NULL;
+ } else {
+ next = field;
+ virSkipToSpace(&next);
+ }
+
+ ret->fields[i] = g_strndup(field, next - field);
+ field = next;
+ }
+
+ return g_steal_pointer(&ret);
+}
+
+
+static void
+virPCIDeviceAliasInfoPrint(virPCIDeviceAliasInfo *info)
+{
+ size_t i;
+
+ for (i = 0; i < G_N_ELEMENTS(info->fields); i++)
+ VIR_DEBUG("%s: '%s'", fieldnames[i], info->fields[i]);
+}
+
+
+static bool
+virPCIDeviceAliasInfoMatch(virPCIDeviceAliasInfo *orig,
+ virPCIDeviceAliasInfo *match,
+ int *wildCardCt)
+{
+ size_t i;
+
+ *wildCardCt = 0;
+
+ for (i = 0; i < G_N_ELEMENTS(orig->fields); i++) {
+ if (STREQ(match->fields[i], "*"))
+ (*wildCardCt)++;
+ else if (STRNEQ(orig->fields[i], match->fields[i]))
+ return false;
+ }
+ return true;
+}
+
+
+/* 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;
+ int currentBestWildcardCt = INT_MAX;
+
+ *moduleName = NULL;
+
+ /* get the modalias values for the device from sysfs */
+ devModAliasPath = virPCIFile(dev->name, "modalias");
+ if (virFileReadAll(devModAliasPath, 100, &devModAliasContent) < 0)
+ return 0;
+
+ 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;
+ }
+
+ virPCIDeviceAliasInfoPrint(devModAliasInfo);
+
+ uname(&unameInfo);
+ modulesAliasPath = g_strdup_printf("/lib/modules/%s/modules.alias",
+ unameInfo.release);
+ if (virFileReadAll(modulesAliasPath,
+ 4 * 1024 * 1024, &modulesAliasContent) < 0) {
+ return -1;
+ }
+
+ /* 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;
+
+ while ((line = strstr(line, "\nalias vfio_pci:"))) {
+ g_autoptr(virPCIDeviceAliasInfo) fileModAliasInfo = NULL;
+ int wildCardCt;
+
+ /* "alias vfio_pci:vNNNNNNNNdNNNNNNNNsvNNNNNNNNsdNNNNNNNNbcNNscNNiNN XXXX\n" */
+ line += strlen("\nalias vfio_pci:");
+ if (!(fileModAliasInfo = virPCIDeviceAliasInfoNew(line)))
+ continue;
+
+ virPCIDeviceAliasInfoPrint(fileModAliasInfo);
+
+ if (virPCIDeviceAliasInfoMatch(devModAliasInfo,
+ fileModAliasInfo, &wildCardCt)) {
+
+ const char *aliasStart = strchr(line, ' ');
+ const char *aliasEnd = NULL;
+ g_autofree char *aliasName = NULL;
+
+ if (!aliasStart) {
+ VIR_WARN("malformed modules.alias vfio_pci: line");
+ continue;
+ }
+
+ aliasStart++;
+ line = aliasEnd = strchrnul(aliasStart, '\n');
+ aliasName = g_strndup(aliasStart, aliasEnd - aliasStart);
+
+ VIR_DEBUG("matching alias '%s' found, %d wildcards",
+ aliasName, wildCardCt);
+
+ if (wildCardCt < currentBestWildcardCt) {
+
+ /* this is a better match than previous */
+ currentBestWildcardCt = wildCardCt;
+ g_free(*moduleName);
+ *moduleName = g_steal_pointer(&aliasName);
+ }
+ }
+ }
+ return 0;
+}
+
+
+#else /* WIN32 */
+
+
+int
+virPCIDeviceFindBestVFIOVariant(virPCIDevice *dev G_GNUC_UNUSED,
+ char **moduleName G_GNUC_UNUSED)
+{
+ virReportSystemError(ENOSYS, "%s",
+ _("VFIO device assignment is not available on this platform"));
+ return -1;
+}
+#endif /* WIN32 */
+
+
static char *
virPCIDeviceReadID(virPCIDevice *dev, const char *id_name)
{
diff --git a/src/util/virpci.h b/src/util/virpci.h
index faca6cf6f9..ca94145207 100644
--- a/src/util/virpci.h
+++ b/src/util/virpci.h
@@ -286,6 +286,8 @@ int virPCIDeviceGetCurrentDriverPathAndName(virPCIDevice *dev,
int virPCIDeviceGetCurrentDriverNameAndType(virPCIDevice *dev,
char **drvName,
virPCIStubDriver *drvType);
+int virPCIDeviceFindBestVFIOVariant(virPCIDevice *dev,
+ char **driverName);
int virPCIDeviceIsPCIExpress(virPCIDevice *dev);
int virPCIDeviceHasPCIExpressLink(virPCIDevice *dev);
--
2.41.0
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