linux-kernel - Re: [PATCH v4 02/30] kho: make debugfs interface optional

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Message-ID: <CA+CK2bC0j=CbTNo=V-dceZEz9mji0yTWkE7QyUzvR1SRCiAJ=A@mail.gmail.com>
Date: Mon, 6 Oct 2025 13:23:11 -0400
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Pratyush Yadav <pratyush@...nel.org>
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Subject: Re: [PATCH v4 02/30] kho: make debugfs interface optional

On Mon, Oct 6, 2025 at 12:55 PM Pratyush Yadav <pratyush@...nel.org> wrote:
>
> Hi Pasha,
>
> On Mon, Sep 29 2025, Pasha Tatashin wrote:
>
> > Currently, KHO is controlled via debugfs interface, but once LUO is
> > introduced, it can control KHO, and the debug interface becomes
> > optional.
> >
> > Add a separate config CONFIG_KEXEC_HANDOVER_DEBUG that enables
> > the debugfs interface, and allows to inspect the tree.
> >
> > Move all debugfs related code to a new file to keep the .c files
> > clear of ifdefs.
> >
> > Co-developed-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
> > Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
> > Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
> [...]
> > @@ -662,36 +660,24 @@ static void __init kho_reserve_scratch(void)
> >       kho_enable = false;
> >  }
> >
> > -struct fdt_debugfs {
> > -     struct list_head list;
> > -     struct debugfs_blob_wrapper wrapper;
> > -     struct dentry *file;
> > +struct kho_out {
> > +     struct blocking_notifier_head chain_head;
> > +     struct mutex lock; /* protects KHO FDT finalization */
> > +     struct kho_serialization ser;
> > +     bool finalized;
> > +     struct kho_debugfs dbg;
> >  };
> >
> > -static int kho_debugfs_fdt_add(struct list_head *list, struct dentry *dir,
> > -                            const char *name, const void *fdt)
> > -{
> > -     struct fdt_debugfs *f;
> > -     struct dentry *file;
> > -
> > -     f = kmalloc(sizeof(*f), GFP_KERNEL);
> > -     if (!f)
> > -             return -ENOMEM;
> > -
> > -     f->wrapper.data = (void *)fdt;
> > -     f->wrapper.size = fdt_totalsize(fdt);
> > -
> > -     file = debugfs_create_blob(name, 0400, dir, &f->wrapper);
> > -     if (IS_ERR(file)) {
> > -             kfree(f);
> > -             return PTR_ERR(file);
> > -     }
> > -
> > -     f->file = file;
> > -     list_add(&f->list, list);
> > -
> > -     return 0;
> > -}
> > +static struct kho_out kho_out = {
> > +     .chain_head = BLOCKING_NOTIFIER_INIT(kho_out.chain_head),
> > +     .lock = __MUTEX_INITIALIZER(kho_out.lock),
> > +     .ser = {
> > +             .track = {
> > +                     .orders = XARRAY_INIT(kho_out.ser.track.orders, 0),
> > +             },
> > +     },
> > +     .finalized = false,
> > +};
>
> There is already one definition for struct kho_out and a static struct
> kho_out early in the file. This is a second declaration and definition.
> And I was super confused when I saw patch 3 since it seemed to be making
> unrelated changes to this struct (and removing an instance of this,
> which should be done in this patch instead). In fact, this patch doesn't
> even build due to this problem. I think some patch massaging is needed
> to fix this all up.

Let me fix it. I Plan to send a separate series only with KHO changes
from LUO, so we can expedite its landing.

Pasha

>
> >
> >  /**
> >   * kho_add_subtree - record the physical address of a sub FDT in KHO root tree.
> [...]
>
> --
> Regards,
> Pratyush Yadav