Re: [PATCH v2 4/5] media: Add flags to tell whether to take graph mutex for an IOCTL

[Shuah Khan <shuahkh@osg.samsung.com>]

On 05/04/2016 05:20 AM, Sakari Ailus wrote:
> New IOCTLs (especially for the request API) do not necessarily need the
> graph mutex acquired. Leave this up to the drivers.

Sakari,

Does this mean drivers have to hold the graph mutex as needed?
My concern with this is that we will have graph_mutex holds in
driver code in addition to the ones we have now. My concern with
referencing graph_mutex from driver code is lack of abstraction.
If we ever need to change grahp-mutex in the media-core, if it
is exposed to drivers, then there will be lot of changes.

Could we look into avoiding drivers referencing graph_mutex
directly?

thanks,
-- Shuah

> 
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> ---
>  drivers/media/media-device.c | 47 ++++++++++++++++++++++++++------------------
>  1 file changed, 28 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
> index 39fe07f..8aef5b8 100644
> --- a/drivers/media/media-device.c
> +++ b/drivers/media/media-device.c
> @@ -390,21 +390,26 @@ static long copy_arg_to_user_nop(void __user *uarg, void *karg,
>  }
>  #endif
>  
> -#define MEDIA_IOC_ARG(__cmd, func, from_user, to_user)	\
> -	[_IOC_NR(MEDIA_IOC_##__cmd)] = {		\
> -		.cmd = MEDIA_IOC_##__cmd,		\
> +/* Do acquire the graph mutex */
> +#define MEDIA_IOC_FL_GRAPH_MUTEX	BIT(0)
> +
> +#define MEDIA_IOC_ARG(__cmd, func, fl, from_user, to_user)		\
> +	[_IOC_NR(MEDIA_IOC_##__cmd)] = {				\
> +		.cmd = MEDIA_IOC_##__cmd,				\
>  		.fn = (long (*)(struct media_device *, void *))func,	\
> -		.arg_from_user = from_user,		\
> -		.arg_to_user = to_user,			\
> +		.flags = fl,						\
> +		.arg_from_user = from_user,				\
> +		.arg_to_user = to_user,					\
>  	}
>  
> -#define MEDIA_IOC(__cmd, func)						\
> -	MEDIA_IOC_ARG(__cmd, func, copy_arg_from_user, copy_arg_to_user)
> +#define MEDIA_IOC(__cmd, func, fl)					\
> +	MEDIA_IOC_ARG(__cmd, func, fl, copy_arg_from_user, copy_arg_to_user)
>  
>  /* the table is indexed by _IOC_NR(cmd) */
>  struct media_ioctl_info {
>  	unsigned int cmd;
>  	long (*fn)(struct media_device *dev, void *arg);
> +	unsigned short flags;
>  	long (*arg_from_user)(void *karg, void __user *uarg, unsigned int cmd);
>  	long (*arg_to_user)(void __user *uarg, void *karg, unsigned int cmd);
>  };
> @@ -449,9 +454,13 @@ static long __media_device_ioctl(
>  
>  	info->arg_from_user(karg, arg, cmd);
>  
> -	mutex_lock(&dev->graph_mutex);
> +	if (info->flags & MEDIA_IOC_FL_GRAPH_MUTEX)
> +		mutex_lock(&dev->graph_mutex);
> +
>  	ret = info->fn(dev, karg);
> -	mutex_unlock(&dev->graph_mutex);
> +
> +	if (info->flags & MEDIA_IOC_FL_GRAPH_MUTEX)
> +		mutex_unlock(&dev->graph_mutex);
>  
>  	if (ret)
>  		return ret;
> @@ -460,11 +469,11 @@ static long __media_device_ioctl(
>  }
>  
>  static const struct media_ioctl_info ioctl_info[] = {
> -	MEDIA_IOC(DEVICE_INFO, media_device_get_info),
> -	MEDIA_IOC(ENUM_ENTITIES, media_device_enum_entities),
> -	MEDIA_IOC(ENUM_LINKS, media_device_enum_links),
> -	MEDIA_IOC(SETUP_LINK, media_device_setup_link),
> -	MEDIA_IOC(G_TOPOLOGY, media_device_get_topology),
> +	MEDIA_IOC(DEVICE_INFO, media_device_get_info, MEDIA_IOC_FL_GRAPH_MUTEX),
> +	MEDIA_IOC(ENUM_ENTITIES, media_device_enum_entities, MEDIA_IOC_FL_GRAPH_MUTEX),
> +	MEDIA_IOC(ENUM_LINKS, media_device_enum_links, MEDIA_IOC_FL_GRAPH_MUTEX),
> +	MEDIA_IOC(SETUP_LINK, media_device_setup_link, MEDIA_IOC_FL_GRAPH_MUTEX),
> +	MEDIA_IOC(G_TOPOLOGY, media_device_get_topology, MEDIA_IOC_FL_GRAPH_MUTEX),
>  };
>  
>  static long media_device_ioctl(struct file *filp, unsigned int cmd,
> @@ -510,11 +519,11 @@ static long from_user_enum_links32(void *karg, void __user *uarg,
>  #define MEDIA_IOC_ENUM_LINKS32		_IOWR('|', 0x02, struct media_links_enum32)
>  
>  static const struct media_ioctl_info compat_ioctl_info[] = {
> -	MEDIA_IOC(DEVICE_INFO, media_device_get_info),
> -	MEDIA_IOC(ENUM_ENTITIES, media_device_enum_entities),
> -	MEDIA_IOC_ARG(ENUM_LINKS32, media_device_enum_links, from_user_enum_links32, copy_arg_to_user_nop),
> -	MEDIA_IOC(SETUP_LINK, media_device_setup_link),
> -	MEDIA_IOC(G_TOPOLOGY, media_device_get_topology),
> +	MEDIA_IOC(DEVICE_INFO, media_device_get_info, MEDIA_IOC_FL_GRAPH_MUTEX),
> +	MEDIA_IOC(ENUM_ENTITIES, media_device_enum_entities, MEDIA_IOC_FL_GRAPH_MUTEX),
> +	MEDIA_IOC_ARG(ENUM_LINKS32, media_device_enum_links, MEDIA_IOC_FL_GRAPH_MUTEX, from_user_enum_links32, copy_arg_to_user_nop),
> +	MEDIA_IOC(SETUP_LINK, media_device_setup_link, MEDIA_IOC_FL_GRAPH_MUTEX),
> +	MEDIA_IOC(G_TOPOLOGY, media_device_get_topology, MEDIA_IOC_FL_GRAPH_MUTEX),
>  };
>  
>  static long media_device_compat_ioctl(struct file *filp, unsigned int cmd,
>