Re: [PATCH for-7.2 v2 16/20] device_tree.c: support string props in fdt_format_node()

[David Gibson]

On Wed, Aug 10, 2022 at 04:40:18PM -0300, Daniel Henrique Barboza wrote:
> 
> 
> On 8/8/22 01:36, David Gibson wrote:
> > On Fri, Aug 05, 2022 at 06:39:44AM -0300, Daniel Henrique Barboza wrote:
> > > To support printing string properties in 'info fdt' we need to determine
> > > whether a void data might contain a string.
> > 
> > Oh... sorry, obviously I hadn't read these later patches when I
> > complained about the command not printing property values.
> > 
> > > 
> > > We do that by casting the void data to a string array and:
> > > 
> > > - check if the array finishes with a null character
> > > - check if all characters are printable
> > 
> > This won't handle the case of the "string list" several strings tacked
> > together, separated by their terminating \0 characters.
> 
> Hmmmm how is this printed? Should we concatenate them? Replace the \0
> with a whitespace? Or ignore the zero and concatenate them?
> 
> E.g. this is a\0string\0list
> 
> Should we print it as:
> 
> this is astringlist
> 
> or
> 
> this is a string list ?

Well, if you're going for dts like output, which you seem to be, you
have two options:

1) Escape the medial nulls

        "this\0is\0a\0string\0list"

2) Multiple strings:

        "this", "is", "a", "string", "list"

Both forms are allowed in dts and will result in an identical
bytestring in the property.

> > > If both conditions are met, we'll consider it to be a string data type
> > > and print it accordingly. After this change, 'info fdt' is now able to
> > > print string properties. Here's an example with the ARM 'virt' machine:
> > > 
> > > (qemu) info fdt /chosen
> > > chosen {
> > >      stdout-path = '/pl011@9000000'
> > >      rng-seed;
> > >      kaslr-seed;
> > > }
> > > 
> > > Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
> > > ---
> > >   softmmu/device_tree.c | 25 ++++++++++++++++++++++++-
> > >   1 file changed, 24 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/softmmu/device_tree.c b/softmmu/device_tree.c
> > > index 3fb07b537f..8691c3ccc0 100644
> > > --- a/softmmu/device_tree.c
> > > +++ b/softmmu/device_tree.c
> > > @@ -663,6 +663,24 @@ void qemu_fdt_qmp_dumpdtb(const char *filename, 
> > > Error **errp)
> > >       error_setg(errp, "Error when saving machine FDT to file %s", 
> > > filename);
> > >   }
> > > +static bool fdt_prop_is_string(const void *data, int size)
> > > +{
> > > +    const char *str = data;
> > > +    int i;
> > > +
> > > +    if (size <= 0 || str[size - 1] != '\0') {
> > > +        return false;
> > > +    }
> > > +
> > > +    for (i = 0; i < size - 1; i++) {
> > > +        if (!g_ascii_isprint(str[i])) {
> > > +            return false;
> > > +        }
> > > +    }
> > > +
> > > +    return true;
> > > +}
> > > +
> > >   static void fdt_format_node(GString *buf, int node, int depth)
> > >   {
> > >       const struct fdt_property *prop = NULL;
> > > @@ -681,7 +699,12 @@ static void fdt_format_node(GString *buf, int node, 
> > > int depth)
> > >           prop = fdt_get_property_by_offset(fdt, property, &prop_size);
> > >           propname = fdt_string(fdt, fdt32_to_cpu(prop->nameoff));
> > > -        g_string_append_printf(buf, "%*s%s;\n", padding, "", propname);
> > > +        if (fdt_prop_is_string(prop->data, prop_size)) {
> > > +            g_string_append_printf(buf, "%*s%s = '%s'\n",
> > > +                                   padding, "", propname, prop->data);
> > 
> > If you're going for dts like output, I'd suggest going all the way.
> > That means \" instead of \' and a ';' at the end of the line.
> > 
> > > +        } else {
> > > +            g_string_append_printf(buf, "%*s%s;\n", padding, "", 
> > > propname);
> > > +        }
> > >       }
> > >       padding -= 4;
> > 
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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