[PATCH] powerpc: kexec_file: Fix error code when trying to load kdump kernel

[Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>]

kexec_file_load() on powerpc doesn't support kdump kernels yet, so it
returns -ENOTSUPP in that case.

I've recently learned that this errno is internal to the kernel and isn't
supposed to be exposed to userspace. Therefore, change to -EOPNOTSUPP which
is defined in an uapi header.

This does indeed make kexec-tools happier. Before the patch, on ppc64le:

  # ~bauermann/src/kexec-tools/build/sbin/kexec -s -p /boot/vmlinuz
  kexec_file_load failed: Unknown error 524

After the patch:

  # ~bauermann/src/kexec-tools/build/sbin/kexec -s -p /boot/vmlinuz
  kexec_file_load failed: Operation not supported

Fixes: a0458284f062 ("powerpc: Add support code for kexec_file_load()")
Reported-by: Dave Young <dyoung@redhat.com>
Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/machine_kexec_file_64.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

This is a minor issue, but since it's a simple patch it might be worth
applying it to stable branches.

This is the kexec-tools thread where this problem was brought up:

https://lists.infradead.org/pipermail/kexec/2018-March/020346.html

And this is an instance of a similar fix being applied elsewhere in the
kernel, for the same reasons:

https://patchwork.kernel.org/patch/8490791/

The test shown in the commit log was made using Hari Bathini's patch
adding kexec_file_load() support to kexec-tools in ppc64.

diff --git a/arch/powerpc/kernel/machine_kexec_file_64.c b/arch/powerpc/kernel/machine_kexec_file_64.c
index e4395f937d63..45e0b7d5f200 100644
--- a/arch/powerpc/kernel/machine_kexec_file_64.c
+++ b/arch/powerpc/kernel/machine_kexec_file_64.c
@@ -43,7 +43,7 @@ int arch_kexec_kernel_image_probe(struct kimage *image, void *buf,
 
 	/* We don't support crash kernels yet. */
 	if (image->type == KEXEC_TYPE_CRASH)
-		return -ENOTSUPP;
+		return -EOPNOTSUPP;
 
 	for (i = 0; i < ARRAY_SIZE(kexec_file_loaders); i++) {
 		fops = kexec_file_loaders[i];