Re: [PATCH] hw/ppc/pnv: Improve kernel/initrd load failure error messages

[Peter Maydell <peter.maydell@linaro.org>]

On Mon, 13 Oct 2025 at 08:02, Vishal Chourasia <vishalc@linux.ibm.com> wrote:
>
> On Tue, Oct 07, 2025 at 02:29:52PM +0100, Peter Maydell wrote:
> > On Tue, 7 Oct 2025 at 13:59, Vishal Chourasia <vishalc@linux.ibm.com> wrote:
> > >
> > > When QEMU fails to load the kernel or initrd image, it previously emitted
> > > a generic error message such as:
> > >
> > >   qemu-system-ppc64: Could not load kernel 'vmlinux'
> > >
> > > This provides little context on why the failure occurred, which can make
> > > debugging difficult, especially for new users or when dealing with large
> > > images.
> > >
> > > The new messages also include the configured size limits (in MiB) to help
> > > users verify that their image files are within acceptable bounds.
> >
> > >          if (kernel_size < 0) {
> > >              error_report("Could not load kernel '%s'",
> > >                           machine->kernel_filename);
> > > +            error_report(
> > > +                "Possible reasons: file not found, permission denied, or size "
> > > +                "exceeds the maximum supported limit (%ld MiB).",
> > > +                KERNEL_MAX_SIZE / 1024 / 1024);
> > >              exit(1);
> > >          }
> >
> > Rather than printing a list of reasons why the load might
> > have failed, I think it would be better if we enhanced
> > the error handling in load_image_targphys() and friends
> > (i.e. use Error), so that these functions can report back
> > to the caller exactly why they failed and then the caller
> > can give that error message to the user. That way we can
> > improve the error reporting for every board that uses
> > these load functions.
> Hello Peter,
>
> Wouldn't it be better to print the error inside the function itself.

No, because some users of this family of load functions
use a sequence of calls to handle different possible
formats. We don't want the function to load file format A
to print any errors if we're then going to continue and
successfully load the file as format B.

More generally, our usual coding practice for functions
is that they use Error to tell the caller what went wrong,
and it's the caller that then gets to decide whether they
want to print an error and exit, tell the monitor about
an error, or just continue to try something else instead.

-- PMM