1 files changed, 32 insertions, 4 deletions

diff --git a/src/libsystemd/sd-hwdb/sd-hwdb.c b/src/libsystemd/sd-hwdb/sd-hwdb.c
index 811a60f0c3..a8c6376302 100644
--- a/src/libsystemd/sd-hwdb/sd-hwdb.c
+++ b/src/libsystemd/sd-hwdb/sd-hwdb.c
@@ -164,10 +164,38 @@ static int hwdb_add_property(sd_hwdb *hwdb, const struct trie_value_entry_f *ent
                 entry2 = (const struct trie_value_entry2_f *)entry;
                 old = ordered_hashmap_get(hwdb->properties, key);
                 if (old) {
-                        /* on duplicates, we order by filename and line-number */
-                        r = strcmp(trie_string(hwdb, entry2->filename_off), trie_string(hwdb, old->filename_off));
-                        if (r < 0 ||
-                            (r == 0 && entry2->line_number < old->line_number))
+                        /* On duplicates, we order by filename priority and line-number.
+                         *
+                         *
+                         * v2 of the format had 64 bits for the line number.
+                         * v3 reuses top 32 bits of line_number to store the priority.
+                         * We check the top bits — if they are zero we have v2 format.
+                         * This means that v2 clients will print wrong line numbers with
+                         * v3 data.
+                         *
+                         * For v3 data: we compare the priority (of the source file)
+                         * and the line number.
+                         *
+                         * For v2 data: we rely on the fact that the filenames in the hwdb
+                         * are added in the order of priority (higher later), because they
+                         * are *processed* in the order of priority. So we compare the
+                         * indices to determine which file had higher priority. Comparing
+                         * the strings alphabetically would be useless, because those are
+                         * full paths, and e.g. /usr/lib would sort after /etc, even
+                         * though it has lower priority. This is not reliable because of
+                         * suffix compression, but should work for the most common case of
+                         * /usr/lib/udev/hwbd.d and /etc/udev/hwdb.d, and is better than
+                         * not doing the comparison at all.
+                         */
+                        bool lower;
+
+                        if (entry2->file_priority == 0)
+                                lower = entry2->filename_off < old->filename_off ||
+                                        (entry2->filename_off == old->filename_off && entry2->line_number < old->line_number);
+                        else
+                                lower = entry2->file_priority < old->file_priority ||
+                                        (entry2->file_priority == old->file_priority && entry2->line_number < old->line_number);
+                        if (lower)
                                 return 0;
                 }
         }