linux-kernel - Re: [RFCv2][PATCH] flexible array implementation

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Message-ID: <4A66868F.4010001@cn.fujitsu.com>
Date:	Wed, 22 Jul 2009 11:25:03 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
CC:	akpm@...ux-foundation.org, containers@...ts.linux-foundation.org,
	bblum@...gle.com, linux-kernel@...r.kernel.org, menage@...gle.com,
	vda.linux@...glemail.com, mikew@...gle.com
Subject: Re: [RFCv2][PATCH] flexible array implementation

> +/**
> + * flex_array_put - copy data into the array at @element_nr
> + * @src:	address of data to copy into the array
> + * @element_nr:	index of the position in which to insert
> + * 		the new element.

@fa and @flags are not documented.

> + *
> + * Note that this *copies* the contents of @src into
> + * the array.  If you are trying to store an array of
> + * pointers, make sure to pass in &ptr instead of ptr.
> + *
> + * Locking must be provided by the caller.
> + */
> +int flex_array_put(struct flex_array *fa, int element_nr, void *src, gfp_t flags)
> +{
> +	int part_nr = fa_element_to_part_nr(fa, element_nr);
> +	struct flex_array_part *part;
> +	void *dst;
> +
> +	part = __fa_get_part(fa, part_nr, flags);
> +	if (!part)
> +		return -ENOMEM;

So this may allocate memory, and has disavantages:

- If flex_array_put() is called in atomic context, flags has to be GFP_ATOMIC.
- and thus it may fail.

Since we pass the total_elem to flex_array_alloc(), how about add a flag,
and if the flag is set, the alloc() will also allocate all fa_parts?

And add __flex_array_put(), which assumes fa_parts has been allocated.

> +	dst = &part->elements[offset_inside_part(fa, element_nr)];
> +	memcpy(dst, src, fa->element_size);
> +	return 0;
> +}
> +
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