[Libguestfs] [PATCH] inspect: Include more information for augeas parse errors (RHBZ#1229119)

[Richard W.M. Jones]

If Augeas fails to parse a file, more information is available in at
least these fields:

><fs> aug-ls /augeas/files/etc/fstab/error
/augeas/files/etc/fstab/error/char
/augeas/files/etc/fstab/error/lens
/augeas/files/etc/fstab/error/line
/augeas/files/etc/fstab/error/message
/augeas/files/etc/fstab/error/pos

Pull out some of these fields and add them to the error message.
The new error message looks like this:

  virt-v2v: error: libguestfs error: /etc/fstab:17:4: augeas parse failure:
  Iterated lens matched less than it should

This updates commit 279addeb7dd4f5f2446a3995eb7704980c08b5ff.
---
 src/inspect-fs-unix.c | 32 ++++++++++++++++++++++++--------
 1 file changed, 24 insertions(+), 8 deletions(-)

diff --git a/src/inspect-fs-unix.c b/src/inspect-fs-unix.c
index 968aa40..4fac7f4 100644
--- a/src/inspect-fs-unix.c
+++ b/src/inspect-fs-unix.c
@@ -1985,7 +1985,6 @@ inspect_with_augeas (guestfs_h *g, struct inspect_fs *fs,
   CLEANUP_FREE char *pathexpr = NULL;
   CLEANUP_FREE_STRING_LIST char **matches = NULL;
   char **match;
-  size_t len;
 
   /* Security: Refuse to do this if a config file is too large. */
   for (i = 0; configfiles[i] != NULL; ++i) {
@@ -2023,16 +2022,33 @@ inspect_with_augeas (guestfs_h *g, struct inspect_fs *fs,
     goto out;
 
   /* Check that augeas did not get a parse error for any of the configfiles,
-   * otherwise we are silently missing information. */
+   * otherwise we are silently missing information.
+   */
   matches = guestfs_aug_match (g, "/augeas/files//error");
   for (match = matches; *match != NULL; ++match) {
     for (i = 0; configfiles[i] != NULL; ++i) {
-      len = strlen (configfiles[i]);
-      if (strlen (*match) == (13 /* len(/augeas/files) */ + len + 6 /* len(/error) */) &&
-          STRPREFIX(*match, "/augeas/files") &&
-          STREQLEN(*match + 13, configfiles[i], len) &&
-          STREQ(*match + 13 + len, "/error")) {
-        error (g, _("augeas could not parse %s"), configfiles[i]);
+      CLEANUP_FREE char *errorpath =
+        safe_asprintf (g, "/augeas/files%s/error", configfiles[i]);
+
+      if (STREQ (*match, errorpath)) {
+        /* Get the various error details. */
+        guestfs_push_error_handler (g, NULL, NULL);
+        CLEANUP_FREE char *messagepath =
+          safe_asprintf (g, "%s/message", errorpath);
+        CLEANUP_FREE char *message = guestfs_aug_get (g, messagepath);
+        CLEANUP_FREE char *linepath =
+          safe_asprintf (g, "%s/line", errorpath);
+        CLEANUP_FREE char *line = guestfs_aug_get (g, linepath);
+        CLEANUP_FREE char *charpath =
+          safe_asprintf (g, "%s/char", errorpath);
+        CLEANUP_FREE char *charp = guestfs_aug_get (g, charpath);
+        guestfs_pop_error_handler (g);
+
+        error (g, _("%s:%s:%s: augeas parse failure: %s"),
+               configfiles[i],
+               line ? : "<none>",
+               charp ? : "<none>",
+               message ? : "<none>");
         goto out;
       }
     }
-- 
2.5.0