Re: [patch 2.6.26-rc3] spi: make spi_board_info.modalias a char array

[Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>]

On Wed, 21 May 2008 17:04:56 -0700 David Brownell <david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org> wrote:

> From: Grant Likely <grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org>
> 
> Currently, 'modalias' in the spi_device structure is a 'const char *'.
> The spi_new_device() function fills in the modalias value from a passed
> in spi_board_info data block.  Since it is a pointer copy, the new
> spi_device remains dependent on the spi_board_info structure after the
> new spi_device is registered (no other fields in spi_device directly
> depend on the spi_board_info structure; all of the other data is copied).
> 
> This causes a problem when dynamically propulating the list of attached
> SPI devices.  For example, in arch/powerpc, the list of SPI devices can
> be populated from data in the device tree.  With the current code, the
> device tree adapter must kmalloc() a new spi_board_info structure for
> each new SPI device it finds in the device tree, and there is no simple
> mechanism in place for keeping track of these allocations.
> 
> This patch changes modalias from a 'const char *' to a fixed char array.
> By copying the modalias string instead of referencing it, the dependency
> on the spi_board_info structure is eliminated and an outside caller does
> not need to maintain a separate spi_board_info allocation for each device.
> 
> If searched through the code to the best of my ability for any references
> to modalias which may be affected by this change and haven't found anything.
> It has been tested with the lite5200b platform in arch/powerpc.
> 

Not for 2.6.26, I assume?

> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c
> @@ -229,7 +229,7 @@ struct spi_device *spi_new_device(struct spi_master *master,
>  	proxy->max_speed_hz = chip->max_speed_hz;
>  	proxy->mode = chip->mode;
>  	proxy->irq = chip->irq;
> -	proxy->modalias = chip->modalias;
> +	strncpy(proxy->modalias, chip->modalias, KOBJ_NAME_LEN);
>  
>  	snprintf(proxy->dev.bus_id, sizeof proxy->dev.bus_id,
>  			"%s.%u", master->dev.bus_id,
> --- a/include/linux/spi/spi.h
> +++ b/include/linux/spi/spi.h
> @@ -82,7 +82,7 @@ struct spi_device {
>  	int			irq;
>  	void			*controller_state;
>  	void			*controller_data;
> -	const char		*modalias;
> +	char			modalias[KOBJ_NAME_LEN];
>  
>  	/*
>  	 * likely need more hooks for more protocol options affecting how

a) strncpy() doesn't null-terminate the dest if it overran.  strlcpy() does.

b) Given the uncertainly over the state of existing code, perhaps we
   should have an explicit check for overflows here, with a WARN_ON()?

c) I think it's better to use sizeof() in the strlcpy() rather than
   duplicating the array size - it's a little more robust in the face
   of future changes and it is more obviously-correct (don't need to go
   elsewhere to check the size of the destination).

d) KOBJ_NAME_LEN no longer exists in linux-next.  I'm not sure where
   it went - Greg and Kay have been up to their usual tricks.

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