kexec: Introduce a member kernel_fd in kexec_info

Utilize the image load interface to export the kernel fd, which points
to the uncompressed kernel and will be passed to kexec_file_load.

The credit goes to the Dave Young, who contributes the original code.

Signed-off-by: Pingfan Liu <piliu@redhat.com>
Co-authored-by: Dave Young <dyoung@redhat.com>
To: kexec@lists.infradead.org
Cc: horms@verge.net.au
Cc: ardb@kernel.org
Cc: jeremy.linton@arm.com
Signed-off-by: Simon Horman <horms@kernel.org>

kexec/kexec.c

@@ -1292,6 +1292,7 @@ static int do_kexec_file_load(int fileind, int argc, char **argv,
 	info.kexec_flags = flags;
 
 	info.file_mode = 1;
+	info.kernel_fd = -1;
 	info.initrd_fd = -1;
 
 	if (!is_kexec_file_load_implemented())
@@ -1337,6 +1338,13 @@ static int do_kexec_file_load(int fileind, int argc, char **argv,
 		return ret;
 	}
 
+       /*
+	* image type specific load functioin detect the capsule kernel type
+	* and create another fd for file load. For example the zboot kernel.
+	*/
+	if (info.kernel_fd != -1)
+		kernel_fd = info.kernel_fd;
+
 	/*
 	 * If there is no initramfs, set KEXEC_FILE_NO_INITRAMFS flag so that
 	 * kernel does not return error with negative initrd_fd.

kexec/kexec.h

@@ -164,6 +164,7 @@ struct kexec_info {
 	unsigned long file_mode :1;
 
 	/* Filled by kernel image processing code */
+	int kernel_fd;
 	int initrd_fd;
 	char *command_line;
 	int command_line_len;