util: Introduce virFileReadLink

We will need to traverse the symlinks one step at the time.
Therefore we need to see where a symlink is pointing to.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

src/libvirt_private.syms

@@ -1616,6 +1616,7 @@ virFileReadAllQuiet;
 virFileReadBufQuiet;
 virFileReadHeaderFD;
 virFileReadLimFD;
+virFileReadLink;
 virFileRelLinkPointsTo;
 virFileRemove;
 virFileRemoveLastComponent;

src/util/virfile.c

@@ -76,6 +76,7 @@
 #include "virutil.h"
 
 #include "c-ctype.h"
+#include "areadlink.h"
 
 #define VIR_FROM_THIS VIR_FROM_NONE
 
@@ -1614,6 +1615,17 @@ virFileIsLink(const char *linkpath)
     return S_ISLNK(st.st_mode) != 0;
 }
 
+/*
+ * Read where symlink is pointing to.
+ *
+ * Returns 0 on success (@linkpath is a successfully read link),
+ *        -1 with errno set upon error.
+ */
+int
+virFileReadLink(const char *linkpath, char **resultpath)
+{
+    return (*resultpath = areadlink(linkpath)) ? 0 : -1;
+}
 
 /*
  * Finds a requested executable file in the PATH env. e.g.:

src/util/virfile.h

@@ -166,6 +166,9 @@ int virFileResolveAllLinks(const char *linkpath,
 int virFileIsLink(const char *linkpath)
     ATTRIBUTE_NONNULL(1) ATTRIBUTE_RETURN_CHECK;
 
+int virFileReadLink(const char *linkpath, char **resultpath)
+    ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2) ATTRIBUTE_RETURN_CHECK;
+
 char *virFindFileInPath(const char *file);
 
 char *virFileFindResource(const char *filename,