Re: [Qemu-devel] [PATCH 1/2] config: qemu_config_parse() return number of config groups

[Eduardo Habkost]

On Mon, Feb 27, 2017 at 06:59:51PM +0100, Markus Armbruster wrote:
> Uh, I totally forgot about this series.  My apologies...
> 
> Eduardo Habkost <address@hidden> writes:
> 
> > Change qemu_config_parse() to return the number of config groups
> > in success and -EINVAL on error. This will allow callers of
> > qemu_config_parse() to check if something was really loaded from
> > the config file.
> >
> > All existing callers of qemu_config_parse() and
> > qemu_read_config_file() only check if the return value was
> > negative, so the change shouldn't affect them.
> 
> Two of them:
> 
> * read_config() maps negative value to -EINVAL.  Callers:
> 
>   - blkdebug_open() passes it on.  As a .bdrv_file_open() method, it's
>     supposed to return -errno on failure.  Good.
> 
> * qemu_read_config_file() maps non-zero value to -EINVAL.  Callers:
> 
>   - qemu_read_default_config_file() maps -EINVAL to zero.  WTF?

qemu_read_config_file() maps -ENOENT to zero, not -EINVAL. It
will ignore the error only if the default config file doesn't
exist (if fopen() sets errno to ENOENT).

> 
>   - main() passes sterror(EINVAL) to error_report().  Good.
> 
> Also: qemu_config_parse() reports errors with error_report().  Let's
> have another look at its callers:
> 
> * read_config() has an Error ** parameter.  Bad.  Care to convert the
>   sucker to Error?

I can do it in a separate patch, unless you believe it must be
done by this patch patch in a single step.

> 
> * qemu_read_config_file() doesn't report errors.  Callers:
> 
>   - qemu_read_default_config_file() doesn't report errors.  Its called
>     by main(), and ...

This means fopen() errors won't get reported. Good catch. I will
send a separate fix.

> 
>   - main() reports with error_report().  Good.
> 
[...]
> 
> I think this mapping to -EINVAL is also superfluous now:
> 
> diff --git a/block/blkdebug.c b/block/blkdebug.c
> index 6117ce5..fbefa9e 100644
> --- a/block/blkdebug.c
> +++ b/block/blkdebug.c
> @@ -252,7 +252,6 @@ static int read_config(BDRVBlkdebugState *s, const char 
> *filename,
>          ret = qemu_config_parse(f, config_groups, filename);
>          if (ret < 0) {
>              error_setg(errp, "Could not parse blkdebug config file");
> -            ret = -EINVAL;
>              goto fail;

Good catch. I will squash it into the patch.

-- 
Eduardo