Re: [PATCH v2 1/6] vfio: platform: add capability to register a reset function

Arnd Bergmann
2015-10-22T10:06:02Z

On Thursday 22 October 2015 11:41:57 Eric Auger wrote:
> In preparation for subsequent changes in reset function lookup,
> lets introduce a dynamic list of reset combos (compat string,
> reset module, reset function). The list can be populated/voided with
> two new functions, vfio_platform_register/unregister_reset. Those are
> not yet used in this patch.
>
> Signed-off-by: Eric Auger <eric.auger@linaro.org>

Looks correct to me now, just a little style comments.

> drivers/vfio/platform/vfio_platform_common.c | 77 +++++++++++++++++++++++++++
> drivers/vfio/platform/vfio_platform_private.h | 7 +++
> 2 files changed, 84 insertions(+)
>
> diff --git a/drivers/vfio/platform/vfio_platform_common.c b/drivers/vfio/platform/vfio_platform_common.c
> index e43efb5..52a4c7b 100644
> --- a/drivers/vfio/platform/vfio_platform_common.c
> +++ b/drivers/vfio/platform/vfio_platform_common.c
> @@ -23,6 +23,15 @@
>
> #include "vfio_platform_private.h"
>
> +struct vfio_platform_reset_node {
> + struct list_head link;
> + char *compat;
> + struct module *owner;
> + vfio_platform_reset_fn_t reset;
> +};
> +
> +static LIST_HEAD(reset_list);
> +static DEFINE_MUTEX(reset_lock);
> static DEFINE_MUTEX(driver_lock);

I wonder if having a single mutex here would be enough. If you don't expect
drivers to register/unregister a lot, you could just use driver_lock here
as well.

> static const struct vfio_platform_reset_combo reset_lookup_table[] = {
> @@ -573,3 +582,71 @@ struct vfio_platform_device *vfio_platform_remove_common(struct device *dev)
> return vdev;
> }
> EXPORT_SYMBOL_GPL(vfio_platform_remove_common);
> +
> +int vfio_platform_register_reset(struct module *reset_owner,
> + const char *compat,
> + vfio_platform_reset_fn_t reset)
> +{
> + struct vfio_platform_reset_node *node, *iter;
> + bool found = false;
> +
> + mutex_lock(&reset_lock);
> + list_for_each_entry(iter, &reset_list, link) {
> + if (!strcmp(iter->compat, compat)) {
> + found = true;
> + break;
> + }
> + }
> + if (found) {
> + mutex_unlock(&reset_lock);
> + return -EINVAL;
> + }

This seems to be an unnecesssary safeguard. I would not bother
with the search, or otherwise do a WARN_ON here.

> + node = kmalloc(sizeof(*node), GFP_KERNEL);
> + if (!node) {
> + mutex_unlock(&reset_lock);
> + return -ENOMEM;
> + }
> +
> + node->compat = kstrdup(compat, GFP_KERNEL);
> + if (!node->compat) {
> + kfree(node);
> + mutex_unlock(&reset_lock);
> + return -ENOMEM;
> + }

If you hold a lock, it's better to use a goto for handling errors
and put the unlock and kfree there. I think it can be avoided
entirely here though:

It should be safe to define the interface as keeping a reference
on the string and not do a kstrdup here. I would expect users to
pass a string literal.

We could even go as far as defining the entire interface as a shim,
like

#define vfio_platform_register_reset(__compat, __reset) \
static struct vfio_platform_reset_node __reset ## _node = { \
.owner = THIS_MODULE, \
.compat = __compat, \
.reset = __reset, \
}; \
__vfio_platform_register_reset(&__reset ## node);

to make the function really simple.

Arnd