Re: [PATCH] of: of_property_read_string return -ENODATA when !length

[Rob Herring <robh+dt@xxxxxxxxxx>]

On Thu, Mar 31, 2022 at 7:46 PM Stefano Stabellini
<sstabellini@xxxxxxxxxx> wrote:
>
> From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
>
> When the length of the string is zero of_property_read_string should
> return -ENODATA according to the description of the function.

Perhaps it is a difference of:

prop;

vs.

prop = "";

Both are 0 length by some definition. The description, '-ENODATA if
property does not have a value', matches the first case.

>
> However, of_property_read_string doesn't check pp->length. If pp->length
> is zero, return -ENODATA.
>
> Without this patch the following command in u-boot:
>
> fdt set /chosen/node property-name
>
> results in of_property_read_string returning -EILSEQ when attempting to
> read property-name. With this patch, it returns -ENODATA as expected.

Why do you care? Do you have a user? There could be an in tree user
that doesn't like this change.

>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
>
> diff --git a/drivers/of/property.c b/drivers/of/property.c
> index 8e90071de6ed..da0f02c98bb2 100644
> --- a/drivers/of/property.c
> +++ b/drivers/of/property.c
> @@ -439,7 +439,7 @@ int of_property_read_string(const struct device_node *np, 
> const char *propname,
>         const struct property *prop = of_find_property(np, propname, NULL);
>         if (!prop)
>                 return -EINVAL;
> -       if (!prop->value)
> +       if (!prop->value || !pp->length)
>                 return -ENODATA;
>         if (strnlen(prop->value, prop->length) >= prop->length)
>                 return -EILSEQ;