[PATCH 3/5] virfile: Introduce virFileMajMinToName

[Michal Privoznik <mprivozn@xxxxxxxxxx>]

This function can be used to translate MAJ:MIN device pair into
/dev/blah name.

Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
---
 src/libvirt_private.syms |  1 +
 src/util/virfile.c       | 53 ++++++++++++++++++++++++++++++++++++++++++++++++
 src/util/virfile.h       |  3 +++
 3 files changed, 57 insertions(+)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 1bbff72263..a705bfd5ef 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1787,6 +1787,7 @@ virFileLength;
 virFileLinkPointsTo;
 virFileLock;
 virFileLoopDeviceAssociate;
+virFileMajMinToName;
 virFileMakeParentPath;
 virFileMakePath;
 virFileMakePathWithMode;
diff --git a/src/util/virfile.c b/src/util/virfile.c
index f89e4bd823..62620862a1 100644
--- a/src/util/virfile.c
+++ b/src/util/virfile.c
@@ -68,6 +68,12 @@
 # include <libdevmapper.h>
 #endif
 
+#ifdef MAJOR_IN_MKDEV
+# include <sys/mkdev.h>
+#elif MAJOR_IN_SYSMACROS
+# include <sys/sysmacros.h>
+#endif
+
 #include "configmake.h"
 #include "intprops.h"
 #include "viralloc.h"
@@ -4317,3 +4323,50 @@ virFileGetMPathTargets(const char *path ATTRIBUTE_UNUSED,
     return -1;
 }
 #endif /* ! WITH_DEVMAPPER */
+
+
+/**
+ * virFileMajMinToName:
+ * @device: device (rdev) to translate
+ * @name: returned name
+ *
+ * For given MAJ:MIN pair (stored in one integer like in st_rdev)
+ * fetch device name, e.g. 8:0 is translated to "/dev/sda".
+ * Caller is responsible for freeing @name when no longer needed.
+ *
+ * Returns 0 on success, -1 otherwise.
+ */
+int
+virFileMajMinToName(unsigned long long device,
+                    char **name)
+{
+    struct stat sb;
+    char *sysfsPath = NULL;
+    char *link = NULL;
+    int ret = -1;
+
+    *name = NULL;
+    if (virAsprintf(&sysfsPath, "/sys/dev/block/%u:%u",
+                    major(device), minor(device)) < 0)
+        goto cleanup;
+
+    if (lstat(sysfsPath, &sb) < 0)
+        goto cleanup;
+
+    if (!S_ISLNK(sb.st_mode)) {
+        errno = ENXIO;
+        goto cleanup;
+    }
+
+    if (virFileReadLink(sysfsPath, &link) < 0)
+        goto cleanup;
+
+    if (virAsprintf(name, "/dev/%s", last_component(link)) < 0)
+        goto cleanup;
+
+    ret = 0;
+ cleanup:
+    VIR_FREE(link);
+    VIR_FREE(sysfsPath);
+    return ret;
+}
diff --git a/src/util/virfile.h b/src/util/virfile.h
index 0db8bf0b99..390940dc98 100644
--- a/src/util/virfile.h
+++ b/src/util/virfile.h
@@ -362,4 +362,7 @@ int virFileGetMPathTargets(const char *path,
                            unsigned long long **devs,
                            size_t *ndevs);
 
+int virFileMajMinToName(unsigned long long device,
+                        char **name);
+
 #endif /* __VIR_FILE_H */
-- 
2.16.1

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