Re: [PATCH V5 1/2] firmware: add more flexible request_firmware_async function

["Luis R. Rodriguez" <mcgrof@kernel.org>]

On Mon, Jul 31, 2017 at 05:09:44PM +0200, Rafał Miłecki wrote:
> From: Rafał Miłecki <rafal@milecki.pl>
> 
> So far we got only one function for loading firmware asynchronously:
> request_firmware_nowait. It didn't allow much customization of firmware
> loading process - there is only one bool uevent argument. Moreover this
> bool also controls user helper in an unclear way.

> Some drivers need more flexible helper providing more options. This
> includes control over uevent or warning for the missing firmware. Of
> course this list may grow up in the future.
> 
> To handle this easily this patch adds a generic request_firmware_async
> function. It takes struct with options as an argument which will allow
> extending it in the future without massive changes.
> 
> This is a really cheap change (no new independent API) which works
> nicely with the existing code. The old request_firmware_nowait is kept
> as a simple helper calling new helper.
> 
> Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
> ---
> V3: Don't expose all FW_OPT_* flags.
>     As Luis noted we want a struct so add struct firmware_opts for real
>     flexibility.
>     Thank you Luis for your review!
> V5: Rebase, update commit message, resend after drvdata discussion
> ---
>  drivers/base/firmware_class.c | 43 ++++++++++++++++++++++++++++++++++---------
>  include/linux/firmware.h      | 15 ++++++++++++++-
>  2 files changed, 48 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
> index b9f907eedbf7..cde85b05e4cb 100644
> --- a/drivers/base/firmware_class.c
> +++ b/drivers/base/firmware_class.c
> @@ -1375,7 +1375,7 @@ static void request_firmware_work_func(struct work_struct *work)
>  	_request_firmware(&fw, fw_work->name, fw_work->device, NULL, 0,
>  			  fw_work->opt_flags);
>  	fw_work->cont(fw, fw_work->context);
> -	put_device(fw_work->device); /* taken in request_firmware_nowait() */
> +	put_device(fw_work->device); /* taken in __request_firmware_nowait() */
>  
>  	module_put(fw_work->module);
>  	kfree_const(fw_work->name);
> @@ -1383,10 +1383,9 @@ static void request_firmware_work_func(struct work_struct *work)
>  }
>  
>  /**
> - * request_firmware_nowait - asynchronous version of request_firmware
> + * __request_firmware_nowait - asynchronous version of request_firmware
>   * @module: module requesting the firmware
> - * @uevent: sends uevent to copy the firmware image if this flag
> - *	is non-zero else the firmware copy must be done manually.
> + * @opt_flags: flags that control firmware loading process, see FW_OPT_*
>   * @name: name of firmware file
>   * @device: device for which firmware is being loaded
>   * @gfp: allocation flags
> @@ -1405,9 +1404,9 @@ static void request_firmware_work_func(struct work_struct *work)
>   *
>   *		- can't sleep at all if @gfp is GFP_ATOMIC.
>   **/
> -int
> -request_firmware_nowait(
> -	struct module *module, bool uevent,
> +static int
> +__request_firmware_nowait(
> +	struct module *module, unsigned int opt_flags,
>  	const char *name, struct device *device, gfp_t gfp, void *context,
>  	void (*cont)(const struct firmware *fw, void *context))
>  {
> @@ -1426,8 +1425,7 @@ request_firmware_nowait(
>  	fw_work->device = device;
>  	fw_work->context = context;
>  	fw_work->cont = cont;
> -	fw_work->opt_flags = FW_OPT_NOWAIT | FW_OPT_FALLBACK |
> -		(uevent ? FW_OPT_UEVENT : FW_OPT_USERHELPER);
> +	fw_work->opt_flags = FW_OPT_NOWAIT | opt_flags;
>  
>  	if (!try_module_get(module)) {
>  		kfree_const(fw_work->name);
> @@ -1440,8 +1438,35 @@ request_firmware_nowait(
>  	schedule_work(&fw_work->work);
>  	return 0;
>  }
> +
> +int request_firmware_nowait(struct module *module, bool uevent,
> +			    const char *name, struct device *device, gfp_t gfp,
> +			    void *context,
> +			    void (*cont)(const struct firmware *fw, void *context))
> +{
> +	unsigned int opt_flags = FW_OPT_FALLBACK |
> +		(uevent ? FW_OPT_UEVENT : FW_OPT_USERHELPER);
> +
> +	return __request_firmware_nowait(module, opt_flags, name, device, gfp,
> +					 context, cont);
> +}
>  EXPORT_SYMBOL(request_firmware_nowait);
>  
> +int __request_firmware_async(struct module *module, const char *name,
> +			     struct firmware_opts *fw_opts, struct device *dev,
> +			     void *context,
> +			     void (*cont)(const struct firmware *fw, void *context))
> +{
> +	unsigned int opt_flags = FW_OPT_UEVENT;

This exposes a long issue. Think -- why do we want this enabled by default? Its
actually because even though the fallback stuff is optional and can be, the uevent
internal flag *also* provides caching support as a side consequence only. We
don't want to add a new API without first cleaning up that mess.

This is a slipery slope and best to clean that up before adding any new API.

That and also Greg recently stated he would like to see at least 3 users of
a feature before adding it. Although I think that's pretty arbitrary, and
considering that request_firmware_into_buf() only has *one* user -- its what
he wishes.

  Luis