linux-kernel - Re: [PATCH 4/6] kexec: A new system call, kexec_file

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Message-ID: <20131204015657.GD3298@localhost.localdomain>
Date:	Wed, 4 Dec 2013 09:56:57 +0800
From:	Baoquan He <bhe@...hat.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
	mjg59@...f.ucam.org, greg@...ah.com, ebiederm@...ssion.com,
	hpa@...or.com
Subject: Re: [PATCH 4/6] kexec: A new system call, kexec_file_load, for in
 kernel kexec

On 11/20/13 at 12:50pm, Vivek Goyal wrote:
> + * that kexec_mutex is held.
> + */

I think kexec_add_buffer is guaranteed to be called before allocating
control pages, why not updating image->control_page after each time
kexec_add_buffer is called. Then when control page is needed, effective
address in crash_kernel region can be given. This can be a little more
efficient.

> +int kexec_add_buffer(struct kimage *image, char *buffer,
> +		unsigned long bufsz, unsigned long memsz,
> +		unsigned long buf_align, unsigned long buf_min,
> +		unsigned long buf_max, int top_down, unsigned long *load_addr)
> +{
> +
> +	unsigned long nr_segments = image->nr_segments, new_nr_segments;
> +	struct kexec_segment *ksegment;
> +	struct kexec_buf *kbuf;
> +
> +	/* Currently adding segment this way is allowed only in file mode */
> +	if (!image->file_mode)
> +		return -EINVAL;
> +
> +	if (nr_segments >= KEXEC_SEGMENT_MAX)
> +		return -EINVAL;
> +
> +	/*
> +	 * Make sure we are not trying to add buffer after allocating
> +	 * control pages. All segments need to be placed first before
> +	 * any control pages are allocated. As control page allocation
> +	 * logic goes through list of segments to make sure there are
> +	 * no destination overlaps.
> +	 */
> +	WARN_ONCE(!list_empty(&image->control_pages), "Adding kexec buffer"
> +			" after allocating control pages\n");
> +
> +	kbuf = kzalloc(sizeof(struct kexec_buf), GFP_KERNEL);
> +	if (!kbuf)
> +		return -ENOMEM;
> +
> +	kbuf->image = image;
> +	kbuf->buffer = buffer;
> +	kbuf->bufsz = bufsz;
> +	/* Align memsz to next page boundary */
> +	kbuf->memsz = ALIGN(memsz, PAGE_SIZE);
> +
> +	/* Align to atleast page size boundary */
> +	kbuf->buf_align = max(buf_align, PAGE_SIZE);
> +	kbuf->buf_min = buf_min;
> +	kbuf->buf_max = buf_max;
> +	kbuf->top_down = top_down;
> +
> +	/* Walk the RAM ranges and allocate a suitable range for the buffer */
> +	walk_system_ram_res(0, -1, kbuf, walk_ram_range_callback);
> +
> +	kbuf->image = NULL;
> +	kfree(kbuf);
> +
> +	/*
> +	 * If range could be found successfully, it would have incremented
> +	 * the nr_segments value.
> +	 */
> +	new_nr_segments = image->nr_segments;
> +
> +	/* A suitable memory range could not be found for buffer */
> +	if (new_nr_segments == nr_segments)
> +		return -EADDRNOTAVAIL;
> +
> +	/* Found a suitable memory range */
> +
> +	ksegment = &image->segment[new_nr_segments - 1];
> +	*load_addr = ksegment->mem;
> +	return 0;
> +}
> +
> +

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