util: new virFileRelLinkPointsTo function

When checking if two filenames point to the same inode (whether
by hardlink or symlink), sometimes one of the names might be
relative.  This convenience function makes it easier to check.

* src/util/virfile.h (virFileRelLinkPointsTo): New prototype.
* src/util/virfile.c (virFileRelLinkPointsTo): New function.
* src/libvirt_private.syms (virfile.h): Export it.
* src/xen/xm_internal.c (xenXMDomainGetAutostart): Use it.

Signed-off-by: Eric Blake <eblake@redhat.com>

src/libvirt_private.syms

@@ -1255,6 +1255,7 @@ virFilePrintf;
 virFileReadAll;
 virFileReadHeaderFD;
 virFileReadLimFD;
+virFileRelLinkPointsTo;
 virFileResolveAllLinks;
 virFileResolveLink;
 virFileRewrite;

src/util/virfile.c

@@ -1368,7 +1368,8 @@ virFileHasSuffix(const char *str,
    && (Stat_buf_1).st_dev == (Stat_buf_2).st_dev)
 
 /* Return nonzero if checkLink and checkDest
-   refer to the same file.  Otherwise, return 0.  */
+ * refer to the same file.  Otherwise, return 0.
+ */
 int
 virFileLinkPointsTo(const char *checkLink,
                     const char *checkDest)
@@ -1382,6 +1383,35 @@ virFileLinkPointsTo(const char *checkLink,
 }
 
 
+/* Return positive if checkLink (residing within directory if not
+ * absolute) and checkDest refer to the same file.  Otherwise, return
+ * -1 on allocation failure (error reported), or 0 if not the same
+ * (silent).
+ */
+int
+virFileRelLinkPointsTo(const char *directory,
+                       const char *checkLink,
+                       const char *checkDest)
+{
+    char *candidate;
+    int ret;
+
+    if (*checkLink == '/')
+        return virFileLinkPointsTo(checkLink, checkDest);
+    if (!directory) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("cannot resolve '%s' without starting directory"),
+                       checkLink);
+        return -1;
+    }
+    if (virAsprintf(&candidate, "%s/%s", directory, checkLink) < 0)
+        return -1;
+    ret = virFileLinkPointsTo(candidate, checkDest);
+    VIR_FREE(candidate);
+    return ret;
+}
+
+
 static int
 virFileResolveLinkHelper(const char *linkpath,
                          bool intermediatePaths,

src/util/virfile.h

@@ -143,7 +143,12 @@ int virFileStripSuffix(char *str,
                        const char *suffix) ATTRIBUTE_RETURN_CHECK;
 
 int virFileLinkPointsTo(const char *checkLink,
-                        const char *checkDest);
+                        const char *checkDest)
+    ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2);
+int virFileRelLinkPointsTo(const char *directory,
+                           const char *checkLink,
+                           const char *checkDest)
+    ATTRIBUTE_NONNULL(2) ATTRIBUTE_NONNULL(3);
 
 int virFileResolveLink(const char *linkpath,
                        char **resultpath) ATTRIBUTE_RETURN_CHECK;

src/xen/xm_internal.c

@@ -1427,25 +1427,24 @@ int
 xenXMDomainGetAutostart(virDomainDefPtr def,
                         int *autostart)
 {
-    char *linkname = xenXMAutostartLinkName(def);
     char *config = xenXMDomainConfigName(def);
     int ret = -1;
 
-    if (!linkname || !config)
+    if (!config)
         goto cleanup;
 
-    *autostart = virFileLinkPointsTo(linkname, config);
+    *autostart = virFileRelLinkPointsTo("/etc/xen/auto/", def->name, config);
     if (*autostart < 0) {
         virReportSystemError(errno,
-                             _("cannot check link %s points to config %s"),
+                             _("cannot check link /etc/xen/auto/%s points "
-                             linkname, config);
+                               "to config %s"),
+                             def->name, config);
         goto cleanup;
     }
 
     ret = 0;
 
  cleanup:
-    VIR_FREE(linkname);
     VIR_FREE(config);
     return ret;
 }