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

[Vipin Sharma <vipinsh@google.com>]

On Mon, May 18, 2026 at 11:29:49AM +0000, tarunsahu@google.com wrote:
> Vipin Sharma <vipinsh@google.com> writes:
> 
> > 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)
> nit: Can add a comment that, once it is failed, retrieved status is saved,
> So it is permanent failure.

I think appropriate place will be the official documentation which is
here include/uapi/linux/liveupdate.h

I don't see it is mentioned in the documentation (yes, code does what
you have said), I will refrain from adding that comment here.

> > +{
> > +	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;
> >  
> >  	map = mmap(NULL, page_size, PROT_READ, MAP_SHARED, mfd, 0);
> >  	if (map == MAP_FAILED)
> > -- 
> > 2.54.0.563.g4f69b47b94-goog