riscv: kexec: add kexec_file_load() support

This patchset implement kexec_file_load() support on riscv, Most of the
code is based on the kexec-tool-patch repo developed by Nick Kossifids.

This patch series enables us to load the riscv vmlinux by specifying
its file decriptor, instead of user-filled buffer via kexec_file_load()
syscall.

Contrary to kexec_load() system call, we reuse the dt blob of the first
kernel to the 2nd explicitly.

To use kexec_file_load() system call, instead of kexec_load(), at kexec
command, '-s' options must be specified. The patch for kexec_tools has
to be apply to riscv architecture source like this:

int elf_riscv_load(int argc, char **argv, const char *buf, off_t len,
	...
	if (info->file_mode) {
		return prepare_kexec_file_options(info);
	}
	...

Add following routine to prepare cmdline_ptr, cmdline_len and initrd_fd
for syscall kexec_file_load:

int prepare_kexec_file_options(struct kexec_info *info)
{
	int fd;
	ssize_t result;
	struct stat stats;

	if (arch_options.cmdline) {
		info->command_line = (char *)arch_options.cmdline;
		info->command_line_len = strlen(info->command_line) + 1;
	}

	if (!arch_options.initrd_path) {
		info->initrd_fd = -1;
		return 0;
	}

	fd = open(arch_options.initrd_path, O_RDONLY | _O_BINARY);
	if (fd < 0) {
		fprintf(stderr, "Cannot open `%s': %s\n", arch_options.initrd_path,
				strerror(errno));
		return -EINVAL;
	}
	result = fstat(fd, &stats);
	if (result < 0) {
		close(fd);
		fprintf(stderr, "Cannot stat: %s: %s\n", arch_options.initrd_path,
				strerror(errno));
		return -EINVAL;
	}
	info->initrd_fd = fd;
	return 0;
}

The basic usage of kexec_file is:
1) Reload capture kernel image:
$ kexec -s -l <riscv-vmlinux> --reuse-cmdline

2) Startup capture kernel:
$ kexec -e

For future work:
* Support for kdump and purgatory.
* Support for kernel image verification.
* Support physical address randomization.

Liao Chang (3):
  kexec_file: Fix kexec_file.c build error for riscv platform
  RISC-V: use memcpy for kexec_file mode
  RISC-V: Add kexec_file support

 arch/riscv/Kconfig                     |  11 ++
 arch/riscv/include/asm/kexec.h         |   4 +
 arch/riscv/kernel/Makefile             |   1 +
 arch/riscv/kernel/elf_kexec.c          | 189 +++++++++++++++++++++++++
 arch/riscv/kernel/machine_kexec.c      |   5 +-
 arch/riscv/kernel/machine_kexec_file.c |  14 ++
 include/linux/kexec.h                  |   2 +-
 kernel/kexec_file.c                    |   4 +-
 8 files changed, 226 insertions(+), 4 deletions(-)
 create mode 100644 arch/riscv/kernel/elf_kexec.c
 create mode 100644 arch/riscv/kernel/machine_kexec_file.c

-- 
2.17.1