[libvirt PATCH 14/15] util: new function virPCIDeviceFindBestVFIOVariant()

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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@xxxxxxxxxx>
---
 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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