Re: [RFC PATCH v2 1/6] device_tree: Add qemu_fdt_add_path

[wangyanan (Y)]

Hi David,

On 2021/4/16 12:52, David Gibson wrote:
> On Tue, Apr 13, 2021 at 04:07:40PM +0800, Yanan Wang wrote:
> > From: Andrew Jones <drjones@redhat.com>
> >
> > qemu_fdt_add_path() works like qemu_fdt_add_subnode(), except
> > it also adds any missing subnodes in the path. We also tweak
> > an error message of qemu_fdt_add_subnode().
> >
> > We'll make use of this new function in a coming patch.
> >
> > Signed-off-by: Andrew Jones <drjones@redhat.com>
> > Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
> > ---
> >   include/sysemu/device_tree.h |  1 +
> >   softmmu/device_tree.c        | 45 ++++++++++++++++++++++++++++++++++--
> >   2 files changed, 44 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/sysemu/device_tree.h b/include/sysemu/device_tree.h
> > index 8a2fe55622..ef060a9759 100644
> > --- a/include/sysemu/device_tree.h
> > +++ b/include/sysemu/device_tree.h
> > @@ -121,6 +121,7 @@ uint32_t qemu_fdt_get_phandle(void *fdt, const char *path);
> >   uint32_t qemu_fdt_alloc_phandle(void *fdt);
> >   int qemu_fdt_nop_node(void *fdt, const char *node_path);
> >   int qemu_fdt_add_subnode(void *fdt, const char *name);
> > +int qemu_fdt_add_path(void *fdt, const char *path);
> >   
> >   #define qemu_fdt_setprop_cells(fdt, node_path, property, ...)                 \
> >       do {                                                                      
> > \
> > diff --git a/softmmu/device_tree.c b/softmmu/device_tree.c
> > index 2691c58cf6..8592c7aa1b 100644
> > --- a/softmmu/device_tree.c
> > +++ b/softmmu/device_tree.c
> > @@ -541,8 +541,8 @@ int qemu_fdt_add_subnode(void *fdt, const char *name)
> >   
> >       retval = fdt_add_subnode(fdt, parent, basename);
> >       if (retval < 0) {
> > -        error_report("FDT: Failed to create subnode %s: %s", name,
> > -                     fdt_strerror(retval));
> > +        error_report("%s: Failed to create subnode %s: %s",
> > +                     __func__, name, fdt_strerror(retval));
> >           exit(1);
> >       }
> >   
> > @@ -550,6 +550,47 @@ int qemu_fdt_add_subnode(void *fdt, const char *name)
> >       return retval;
> >   }
> >   
> > +/*
> > + * Like qemu_fdt_add_subnode(), but will add all missing
> > + * subnodes in the path.
> > + */
> > +int qemu_fdt_add_path(void *fdt, const char *path)
> > +{
> > +    char *dupname, *basename, *p;
> > +    int parent, retval = -1;
> > +
> > +    if (path[0] != '/') {
> > +        return retval;
> > +    }
> > +
> > +    parent = fdt_path_offset(fdt, "/");
> Getting the offset for "/" is never needed - it's always 0.
Thanks, will fix it.
> > +    p = dupname = g_strdup(path);
> You shouldn't need the strdup(), see below.
>
> > +
> > +    while (p) {
> > +        *p = '/';
> > +        basename = p + 1;
> > +        p = strchr(p + 1, '/');
> > +        if (p) {
> > +            *p = '\0';
> > +        }
> > +        retval = fdt_path_offset(fdt, dupname);
> The fdt_path_offset_namelen() function exists *exactly* so that you
> can look up partial parths without having to mangle your input
> string.  Just set the namelen right, and it will ignore anything to
> the right of that.
Function fdt_path_offset_namelen() seems more reasonable.

After we call qemu_fdt_add_path() to add "/cpus/cpu-map/socket0/core0" 
successfully,
if we want to add another path like "/cpus/cpu-map/socket0/core1" we 
will get the error
-FDT_ERR_NOTFOUND for each partial path. But actually 
"/cpus/cpu-map/socket0"
already exists, so by using fdt_path_offset_namelen() with right namelen 
we can avoid
the error retval for this part.
> > +        if (retval < 0 && retval != -FDT_ERR_NOTFOUND) {
> > +            error_report("%s: Invalid path %s: %s",
> > +                         __func__, path, fdt_strerror(retval));
> If you're getting an error other than FDT_ERR_NOTFOUND here, chances
> are it's not an invalid path, but a corrupted fdt blob or something
> else.

Right, there can be variable reasons for the fail in addition to the 
invalid path.

> > +            exit(1);
> > +        } else if (retval == -FDT_ERR_NOTFOUND) {
> > +            retval = fdt_add_subnode(fdt, parent, basename);
> > +            if (retval < 0) {
> > +                break;
> > +            }
I found another question here. If path "/cpus/cpu-map/socket0/core0" has 
already
been added, when we want to add another path "/cpus/cpu-map/socket0/core1"
and go here with retval = fdt_add_subnode(fdt, parent, "cpus"), then 
retval will
be -FDT_ERR_EXISTS, but we can't just break the loop in this case.

Am I right of the explanation ?

Thanks,
Yanan
> > +        }
> > +        parent = retval;
> > +    }
> > +
> > +    g_free(dupname);
> > +    return retval;
> > +}
> > +
> >   void qemu_fdt_dumpdtb(void *fdt, int size)
> >   {
> >       const char *dumpdtb = current_machine->dumpdtb;