hw/nvram/fw_cfg: Let fw_cfg_add_from_generator() return boolean value

Commits b6d7e9b66f..a43770df5d simplified the error propagation.
Similarly to commit 6fd5bef10b "qom: Make functions taking Error**
return bool, not void", let fw_cfg_add_from_generator() return a
boolean value, not void.
This allow to simplify parse_fw_cfg() and fixes the error handling
issue reported by Coverity (CID 1430396):

  In parse_fw_cfg():

    Variable assigned once to a constant guards dead code.

    Local variable local_err is assigned only once, to a constant
    value, making it effectively constant throughout its scope.
    If this is not the intent, examine the logic to see if there
    is a missing assignment that would make local_err not remain
    constant.

It's the call of fw_cfg_add_from_generator():

        Error *local_err = NULL;

        fw_cfg_add_from_generator(fw_cfg, name, gen_id, errp);
        if (local_err) {
            error_propagate(errp, local_err);
            return -1;
        }
        return 0;

If it fails, parse_fw_cfg() sets an error and returns 0, which is
wrong. Harmless, because the only caller passes &error_fatal.

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Fixes: Coverity CID 1430396: 'Constant' variable guards dead code (DEADCODE)
Fixes: 6552d87c48 ("softmmu/vl: Let -fw_cfg option take a 'gen_id' argument")
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200721131911.27380-3-philmd@redhat.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/include/hw/nvram/fw_cfg.h b/include/hw/nvram/fw_cfg.h
index bbcf405..f190c42 100644
--- a/include/hw/nvram/fw_cfg.h
+++ b/include/hw/nvram/fw_cfg.h
@@ -304,8 +304,10 @@ void *fw_cfg_modify_file(FWCfgState *s, const char *filename, void *data,
  * will be used; also, a new entry will be added to the file directory
  * structure residing at key value FW_CFG_FILE_DIR, containing the item name,
  * data size, and assigned selector key value.
+ *
+ * Returns: %true on success, %false on error.
  */
-void fw_cfg_add_from_generator(FWCfgState *s, const char *filename,
+bool fw_cfg_add_from_generator(FWCfgState *s, const char *filename,
                                const char *gen_id, Error **errp);
 
 FWCfgState *fw_cfg_init_io_dma(uint32_t iobase, uint32_t dma_iobase,