Re: [PATCH 1/3] of: dynamic: add of_property_alloc() and of_property_free()

[Rob Herring]

On Wed, Jun 1, 2022 at 5:31 PM Tyrel Datwyler <tyreld@xxxxxxxxxxxxx> wrote:
>
> On 5/5/22 12:37, Rob Herring wrote:
> > On Wed, May 04, 2022 at 05:40:31PM +0200, Clément Léger wrote:
> >> Add function which allows to dynamically allocate and free properties.
> >> Use this function internally for all code that used the same logic
> >> (mainly __of_prop_dup()).
> >>
> >> Signed-off-by: Clément Léger <clement.leger@xxxxxxxxxxx>
> >> ---
> >>  drivers/of/dynamic.c | 101 ++++++++++++++++++++++++++++++-------------
> >>  include/linux/of.h   |  16 +++++++
> >>  2 files changed, 88 insertions(+), 29 deletions(-)
> >>
> >> diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
> >> index cd3821a6444f..e8700e509d2e 100644
> >> --- a/drivers/of/dynamic.c
> >> +++ b/drivers/of/dynamic.c
> >> @@ -313,9 +313,7 @@ static void property_list_free(struct property *prop_list)
> >>
> >>      for (prop = prop_list; prop != NULL; prop = next) {
> >>              next = prop->next;
> >> -            kfree(prop->name);
> >> -            kfree(prop->value);
> >> -            kfree(prop);
> >> +            of_property_free(prop);
> >>      }
> >>  }
> >>
> >> @@ -367,48 +365,95 @@ void of_node_release(struct kobject *kobj)
> >>  }
> >>
> >>  /**
> >> - * __of_prop_dup - Copy a property dynamically.
> >> - * @prop:   Property to copy
> >> + * of_property_free - Free a property allocated dynamically.
> >> + * @prop:   Property to be freed
> >> + */
> >> +void of_property_free(const struct property *prop)
> >> +{
> >> +    kfree(prop->value);
> >> +    kfree(prop->name);
> >> +    kfree(prop);
> >> +}
> >> +EXPORT_SYMBOL(of_property_free);
> >> +
> >> +/**
> >> + * of_property_alloc - Allocate a property dynamically.
> >> + * @name:   Name of the new property
> >> + * @value:  Value that will be copied into the new property value
> >> + * @value_len:      length of @value to be copied into the new property value
> >> + * @len:    Length of new property value, must be greater than @value_len
> >
> > What's the usecase for the lengths being different? That doesn't seem
> > like a common case, so perhaps handle it with a NULL value and
> > non-zero length. Then the caller has to deal with populating
> > prop->value.
> >
> >>   * @allocflags:     Allocation flags (typically pass GFP_KERNEL)
> >>   *
> >> - * Copy a property by dynamically allocating the memory of both the
> >> + * Create a property by dynamically allocating the memory of both the
> >>   * property structure and the property name & contents. The property's
> >>   * flags have the OF_DYNAMIC bit set so that we can differentiate between
> >>   * dynamically allocated properties and not.
> >>   *
> >>   * Return: The newly allocated property or NULL on out of memory error.
> >>   */
> >> -struct property *__of_prop_dup(const struct property *prop, gfp_t allocflags)
> >> +struct property *of_property_alloc(const char *name, const void *value,
> >> +                               int value_len, int len, gfp_t allocflags)
> >>  {
> >> -    struct property *new;
> >> +    int alloc_len = len;
> >> +    struct property *prop;
> >> +
> >> +    if (len < value_len)
> >> +            return NULL;
> >>
> >> -    new = kzalloc(sizeof(*new), allocflags);
> >> -    if (!new)
> >> +    prop = kzalloc(sizeof(*prop), allocflags);
> >> +    if (!prop)
> >>              return NULL;
> >>
> >> +    prop->name = kstrdup(name, allocflags);
> >> +    if (!prop->name)
> >> +            goto out_err;
> >> +
> >>      /*
> >> -     * NOTE: There is no check for zero length value.
> >> -     * In case of a boolean property, this will allocate a value
> >> -     * of zero bytes. We do this to work around the use
> >> -     * of of_get_property() calls on boolean values.
> >> +     * Even if the property has no value, it must be set to a
> >> +     * non-null value since of_get_property() is used to check
> >> +     * some values that might or not have a values (ranges for
> >> +     * instance). Moreover, when the node is released, prop->value
> >> +     * is kfreed so the memory must come from kmalloc.
> >
> > Allowing for NULL value didn't turn out well...
> >
> > We know that we can do the kfree because OF_DYNAMIC is set IIRC...
> >
> > If we do 1 allocation for prop and value, then we can test
> > for "prop->value == prop + 1" to determine if we need to free or not.
>
> If its a single allocation do we even need a test? Doesn't kfree(prop) take care
> of the property and the trailing memory allocated for the value?

Yes, it does when it's a single alloc, but it's testing for when
prop->value is not a single allocation because we could have either.

Rob