Re: [PATCH 2/2] selftests/liveupdate: Add helpers to preserve/retrieve FDs

[Pratyush Yadav <pratyush@kernel.org>]

On Mon, May 11 2026, Vipin Sharma wrote:

> Add helper functions to preserve and retrieve file descriptors from an
> LUO session. This allows library users to work with FD preservation.
>
> No functional change intended.
>
> Signed-off-by: Vipin Sharma <vipinsh@google.com>
> Co-developed-by: David Matlack <dmatlack@google.com>
> Signed-off-by: David Matlack <dmatlack@google.com>
> Signed-off-by: Vipin Sharma <vipinsh@google.com>
> ---
>  .../liveupdate/lib/include/libliveupdate.h    |  3 ++
>  .../selftests/liveupdate/lib/liveupdate.c     | 41 +++++++++++++++----
>  2 files changed, 35 insertions(+), 9 deletions(-)
>
> diff --git a/tools/testing/selftests/liveupdate/lib/include/libliveupdate.h b/tools/testing/selftests/liveupdate/lib/include/libliveupdate.h
> index 4390a2737930..2b04b3256382 100644
> --- a/tools/testing/selftests/liveupdate/lib/include/libliveupdate.h
> +++ b/tools/testing/selftests/liveupdate/lib/include/libliveupdate.h
> @@ -26,6 +26,9 @@ int luo_create_session(int luo_fd, const char *name);
>  int luo_retrieve_session(int luo_fd, const char *name);
>  int luo_session_finish(int session_fd);
>  
> +int luo_session_preserve_fd(int session_fd, int fd, __u64 token);
> +int luo_session_retrieve_fd(int session_fd, __u64 token);
> +
>  int create_and_preserve_memfd(int session_fd, int token, const char *data);
>  int restore_and_verify_memfd(int session_fd, int token, const char *expected_data);
>  
> diff --git a/tools/testing/selftests/liveupdate/lib/liveupdate.c b/tools/testing/selftests/liveupdate/lib/liveupdate.c
> index 60121873f685..7bc6707d8bb7 100644
> --- a/tools/testing/selftests/liveupdate/lib/liveupdate.c
> +++ b/tools/testing/selftests/liveupdate/lib/liveupdate.c
> @@ -54,9 +54,35 @@ int luo_retrieve_session(int luo_fd, const char *name)
>  	return arg.fd;
>  }
>  
> +int luo_session_preserve_fd(int session_fd, int fd, __u64 token)
> +{
> +	struct liveupdate_session_preserve_fd arg = {
> +		.size = sizeof(arg),
> +		.fd = fd,
> +		.token = token,
> +	};
> +
> +	if (ioctl(session_fd, LIVEUPDATE_SESSION_PRESERVE_FD, &arg) < 0)
> +		return -errno;
> +
> +	return 0;
> +}
> +
> +int luo_session_retrieve_fd(int session_fd, __u64 token)
> +{
> +	struct liveupdate_session_retrieve_fd arg = {
> +		.size = sizeof(arg),
> +		.token = token,
> +	};
> +
> +	if (ioctl(session_fd, LIVEUPDATE_SESSION_RETRIEVE_FD, &arg) < 0)
> +		return -errno;
> +
> +	return arg.fd;
> +}
> +
>  int create_and_preserve_memfd(int session_fd, int token, const char *data)
>  {
> -	struct liveupdate_session_preserve_fd arg = { .size = sizeof(arg) };
>  	long page_size = sysconf(_SC_PAGE_SIZE);
>  	void *map = MAP_FAILED;
>  	int mfd = -1, ret = -1;
> @@ -75,9 +101,8 @@ int create_and_preserve_memfd(int session_fd, int token, const char *data)
>  	snprintf(map, page_size, "%s", data);
>  	munmap(map, page_size);
>  
> -	arg.fd = mfd;
> -	arg.token = token;
> -	if (ioctl(session_fd, LIVEUPDATE_SESSION_PRESERVE_FD, &arg) < 0)
> +	ret = luo_session_preserve_fd(session_fd, mfd, token);
> +	if (ret)
>  		goto out;
>  
>  	ret = 0;
> @@ -92,15 +117,13 @@ int create_and_preserve_memfd(int session_fd, int token, const char *data)
>  int restore_and_verify_memfd(int session_fd, int token,
>  			     const char *expected_data)
>  {
> -	struct liveupdate_session_retrieve_fd arg = { .size = sizeof(arg) };
>  	long page_size = sysconf(_SC_PAGE_SIZE);
>  	void *map = MAP_FAILED;
>  	int mfd = -1, ret = -1;
>  
> -	arg.token = token;
> -	if (ioctl(session_fd, LIVEUPDATE_SESSION_RETRIEVE_FD, &arg) < 0)
> -		return -errno;
> -	mfd = arg.fd;
> +	mfd = luo_session_retrieve_fd(session_fd, token);
> +	if (mfd < 0)
> +		return mfd;

There is also preserve_fd() in selftests/liveupdate/liveupdate.c which
pretty much does what your luo_session_preserve_fd() does. I think you
should remove it and make its callers use the new library.

LGTM otherwise.

>  
>  	map = mmap(NULL, page_size, PROT_READ, MAP_SHARED, mfd, 0);
>  	if (map == MAP_FAILED)

-- 
Regards,
Pratyush Yadav