[PATCH v3 11/11] kexec: Add option to get crash kernel region size

[Daniel Kiper]

On Fri, Feb 10, 2017 at 04:07:42PM -0600, Eric DeVolder wrote:
> From: Daniel Kiper <daniel.kiper at oracle.com>
>
> From: Daniel Kiper <daniel.kiper at oracle.com>

Hmmm... One is sufficient...

> Crash kernel region size is available via sysfs on Linux running on
> bare metal. However, this does not work when Linux runs as Xen dom0.
> In this case Xen crash kernel region size should be established using
> __HYPERVISOR_kexec_op hypercall (Linux kernel kexec functionality does
> not make a lot of sense in Xen dom0). Sadly hypercalls are not easily
> accessible using shell scripts or something like that. Potentially we
> can check "xl dmesg" output for crashkernel option but this is not nice.
> So, let's add this functionality, for Linux running on bare metal and
> as Xen dom0, to kexec-tools. This way kdump scripts may establish crash
> kernel region size in one way regardless of platform. All burden of
> platform detection lies on kexec-tools.
>
> Figure (and unit) displayed by this new kexec-tools functionality is
> the same as one taken from /sys/kernel/kexec_crash_size.
>
> Signed-off-by: Daniel Kiper <daniel.kiper at oracle.com>
> Signed-off-by: Eric DeVolder <eric.devolder at oracle.com>
> ---
>  kexec/kexec.8 |  3 +++
>  kexec/kexec.c | 20 ++++++++++++++++++++
>  kexec/kexec.h |  4 +++-
>  3 files changed, 26 insertions(+), 1 deletion(-)
>
> diff --git a/kexec/kexec.8 b/kexec/kexec.8
> index f4b39a6..e0131b4 100644
> --- a/kexec/kexec.8
> +++ b/kexec/kexec.8
> @@ -179,6 +179,9 @@ Load a helper image to jump back to original kernel.
>  .TP
>  .BI \-\-reuseinitrd
>  Reuse initrd from first boot.
> +.TP
> +.BI \-\-print-ckr-size
> +Print crash kernel region size, if available.
>
>
>  .SH SUPPORTED KERNEL FILE TYPES AND OPTIONS
> diff --git a/kexec/kexec.c b/kexec/kexec.c
> index a2ba79d..0be1be4 100644
> --- a/kexec/kexec.c
> +++ b/kexec/kexec.c
> @@ -995,6 +995,7 @@ void usage(void)
>  	       "     --mem-max=<addr> Specify the highest memory address to\n"
>  	       "                      load code into.\n"
>  	       "     --reuseinitrd    Reuse initrd from first boot.\n"
> +	       "     --print-ckr-size Print crash kernel region size.\n"
>  	       "     --load-preserve-context Load the new kernel and preserve\n"
>  	       "                      context of current kernel during kexec.\n"
>  	       "     --load-jump-back-helper Load a helper image to jump back\n"
> @@ -1218,6 +1219,22 @@ static int do_kexec_file_load(int fileind, int argc, char **argv,
>  	return ret;
>  }
>
> +static void print_crashkernel_region_size(void)
> +{
> +	uint64_t start = 0, end = 0;

This initialization is not needed.

> +
> +	if (is_crashkernel_mem_reserved()) {
> +		int ret = get_crash_kernel_load_range(&start, &end);

I do not like mixing code with variable declarations.

> +		if (ret != 0) {

if (ret)

> +			fprintf(stderr, "get_crash_kernel_load_range failed.\n");

s/get_crash_kernel_load_range/get_crash_kernel_load_range()/

> +			return;
> +		}
> +	}

Please add empty line here.

> +	if (start != end)

if (!ret && start != end)

There is no guarantee that in case of error nobody touched start and/or
end in get_crash_kernel_load_range() call.

> +		printf("%lu\n", end - start + 1);
> +	else
> +		printf("0\n");
> +}

Daniel