Re: [PATCH] block: Remove trailing newline in format used by error_report API

[Markus Armbruster <armbru@redhat.com>]

Philippe Mathieu-Daudé <philmd@redhat.com> writes:

> The error_report API doesn't want trailing newline characters.
> Remove it, to avoid and error when moving the code around:
>
>   ERROR: Error messages should not contain newlines

Commit 312fd5f2909 has a Coccinelle script.  It should be committed and
re-run.

> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>  block.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/block.c b/block.c
> index 1bdb9c679d..e466d15914 100644
> --- a/block.c
> +++ b/block.c
> @@ -5994,7 +5994,7 @@ void bdrv_img_create(const char *filename, const char *fmt,
           bs = bdrv_open(full_backing, NULL, backing_options, back_flags,
                          &local_err);
           g_free(full_backing);
           if (!bs && size != -1) {
>              /* Couldn't open BS, but we have a size, so it's nonfatal */
>              warn_reportf_err(local_err,
>                              "Could not verify backing image. "
> -                            "This may become an error in future versions.\n");
> +                            "This may become an error in future versions.");
>              local_err = NULL;
>          } else if (!bs) {
>              /* Couldn't open bs, do not have size */

warn_reportf_err() is a convenience function to error_prepend(),
warn_report() and free @local_err.

When @local_err holds a message like "pants on fire", the code before
the patch prints something like

    qemu-system-x86_64: warning: Could not verify backing image. This may become an error in future versions.
    pants on fire

The patch "improves" it to

    qemu-system-x86_64: warning: Could not verify backing image. This may become an error in future versions.pants on fire

General advice: this misuse of warn_reportf_err() is an excusable
mistake, but when you *test* the error path, you can't *not* see that
the actual message is crap.  Test your errors!

Actual improvement:

               warn_reportf_err(local_err, "Could not verify backing image: ");
               error_printf("This may become an error in future versions.\n");

This should print

    qemu-system-x86_64: warning: Could not verify backing image: pants on fire
    This may become an error in future versions.