commit: lookup payload link

Whenever we add a new object file, in addition to lookup if the file is
already present with the same checksum we also check if an object with
the same payload is in the repository.

If a file with the same payload is already present in the repository, we
copy it with `glnx_regfile_copy_bytes` that internally attempts to
create a reflink (ioctl (..., FICLONE, ..)) to the target file if the
file system supports it.  This enables to have objects that share the
payload but have a different inode and xattrs.

Signed-off-by: Giuseppe Scrivano <[email protected]>

src/libostree/ostree-repo-commit.c

@@ -854,6 +854,8 @@ write_content_object (OstreeRepo         *self,
     }
   else
     {
+      gboolean has_payload_object = FALSE;
+
       /* Update size metadata if configured */
       if (indexable && object_file_type == G_FILE_TYPE_REGULAR)
         {
@@ -865,6 +867,41 @@ write_content_object (OstreeRepo         *self,
           repo_store_size_entry (self, actual_checksum, unpacked_size, stbuf.st_size);
         }
 
+      if (actual_payload_checksum)
+        {
+
+          if (!ostree_repo_has_object (self, OSTREE_OBJECT_TYPE_PAYLOAD_LINK, actual_payload_checksum,
+                                       &has_payload_object, cancellable, error))
+            return FALSE;
+
+
+          /* We already have an object with the same payload.  Clone it, if possible.  */
+          if (has_payload_object)
+            {
+              glnx_autofd int fdf = -1;
+              char loose_path_buf[_OSTREE_LOOSE_PATH_MAX];
+              char target_checksum[OSTREE_SHA256_STRING_LEN+1];
+
+              _ostree_loose_path (loose_path_buf, actual_payload_checksum, OSTREE_OBJECT_TYPE_PAYLOAD_LINK, self->mode);
+
+              if (readlinkat (self->objects_dir_fd, loose_path_buf, target_checksum, sizeof (target_checksum)) < 0)
+                return glnx_throw_errno (error);
+
+              _ostree_loose_path (loose_path_buf, target_checksum, OSTREE_OBJECT_TYPE_FILE, self->mode);
+              if (!ot_openat_ignore_enoent (self->objects_dir_fd, loose_path_buf, &fdf, error))
+                return FALSE;
+
+              if (fdf >= 0)
+                {
+                  if (ftruncate (tmpf.fd, 0) < 0)
+                    return glnx_throw_errno (error);
+
+                  if (glnx_regfile_copy_bytes (fdf, tmpf.fd, -1) < 0)
+                    return FALSE;
+                }
+            }
+        }
+
       /* This path is for regular files */
       if (!commit_loose_regfile_object (self, actual_checksum, &tmpf,
                                         uid, gid, mode,