update docs about hardlinked symlinks limitation

(cherry picked from commit d535c6a25d7c43723979e0924fca4f6babb01377)

borg/archive.py

@@ -633,6 +633,9 @@ Number of files: {0.stats.nfiles}'''.format(
             return 'b'  # block device
 
     def process_symlink(self, path, st):
+        # note: we can not support hardlinked symlinks,
+        #       due to the dual-use of item[b'source'], see issue #2343:
+        # hardlinked symlinks will be archived [and extracted] as non-hardlinked symlinks.
         with backup_io():
             source = os.readlink(path)
         item = {b'path': make_path_safe(path), b'source': source}

docs/faq.rst

@@ -94,6 +94,9 @@ Which file types, attributes, etc. are *not* preserved?
       Archive extraction has optional support to extract all-zero chunks as
       holes in a sparse file.
     * filesystem specific attributes, like ext4 immutable bit, see :issue:`618`.
+    * For hardlinked symlinks, the hardlinking can not be archived (and thus,
+      the hardlinking will not be done at extraction time). The symlinks will
+      be archived and extracted as non-hardlinked symlinks, see :issue:`2379`.
 
 Are there other known limitations?
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