Re: [PATCH 0/2] Kexec jump: The first step to kexec base hibernation

[Pavel Machek <pavel@ucw.cz>]

Hi!

Looks interesting... but I was feeling strange dejavu reading
this... and that's because you pasted the changelog twice :-).

> Kexec base hibernation has some potential advantages over uswsusp and
> suspend2. Some most obvious advantages are:
> 
> 1. The hibernation image size can exceed half of memory size easily.

Yes.

> 2. The hibernation image can be written to and read from almost
>    anywhere, such as USB disk, NFS.

We could do USB disk with uswsusp... NFS would be harder.

How fast can kexec boot secondary kernel?

> This patch implements the functionality of "jumping from kexeced
> kernel to original kernel". That is, the following sequence is
> possible:
> 
> 1. Boot a kernel A
> 2. Work under kernel A
> 3. Kexec another kernel B in kernel A
> 4. Work under kernel B
> 5. Jump from kernel B to kernel A
> 6. Continue work under kernel A

Nice!

> 2. Compile the kexec-tools with kdump and kjump patches added, the
>    kdump patch can be found at:
> 
> http://lse.sourceforge.net/kdump/patches/kexec-tools-1.101-dkump10.patch

I got 404 error :-(.

> 3. Boot compiled kernel, the reserved crash kernel memory region must
>    be added to kernel command line as following:
> 
>    crashkernel=<XX>M@<XX>M
> 
>    Where, <XX> should be replaced by the real memory size and position.

How much memory do you suggest to reserve? 64M? 

> 7. In the kexec booted kernel, trigger the jumping back with following
>    shell command.
> 
>    echo <a>:<b> > /sys/power/resume
> 
>    Where <a> and <b> is non-negative integer, at least one of them must
>    be non-zero.

What does a and b mean?

[Was it more than three copies? If they were non-identical, assume I
read some random one].

> +/* Adds the kexec_backup= command line parameter to command line. */
> +static int cmdline_add_backup(char *cmdline, unsigned long addr)
> +{
> +	int cmdlen, len, align = 1024;
> +	char str[30], *ptr;
> +
> +	/* Passing in kexec_backup=xxxK format. Saves space required in cmdline.
> +	 * Ensure 1K alignment*/
> +	if (addr%align)
> +		return -1;
> +	addr = addr/align;
> +	ptr = str;
> +	strcpy(str, " kexec_backup=");
> +	ptr += strlen(str);
> +	ultoa(addr, ptr);
> +	strcat(str, "K");
> +	len = strlen(str);
> +	cmdlen = strlen(cmdline) + len;
> +	if (cmdlen > (COMMAND_LINE_SIZE - 1))
> +		die("Command line overflow\n");
> +	strcat(cmdline, str);
> +#if 0
> +		printf("Command line after adding backup\n");
> +		printf("%s\n", cmdline);
> +#endif
> +	return 0;
> +}

printf()? ...and please remove out commented code.
									Pavel
-- 
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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html