Re: [PATCH v2] liveupdate: add LIVEUPDATE_SESSION_GET_NAME ioctl

[Pasha Tatashin <pasha.tatashin@soleen.com>]

On 04-17 01:36, luca.boccassi@gmail.com wrote:
> From: Luca Boccassi <luca.boccassi@gmail.com>
> 
> Userspace when requesting a session via the ioctl specifies a name and
> gets a FD, but then there is no ioctl to go back the other way and get
> the name given a LUO session FD. This is problematic especially when
> there is a userspace orchestrator that wants to check what FDs it is
> handling for clients without having to do manual string scraping of
> procfs, or without procfs at all.
> 
> Add a ioctl to simply get the name from an FD.
> 
> Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>
> ---
> This was requested by Lennart and Christian when discussing integration
> with systemd for LUO management.
> 
> v2: apply one fix from bot review about cleanup on error path:
>     https://sashiko.dev/#/patchset/20260415184536.1155220-1-luca.boccassi%40gmail.com
>     the other comments are invalid: luo is not a kmod, and the write hooks are not set up

Please split into two patches, and also CC to kernel-linux.
> 
>  include/uapi/linux/liveupdate.h               | 19 +++++
>  kernel/liveupdate/luo_session.c               | 13 ++++
>  .../testing/selftests/liveupdate/liveupdate.c | 71 +++++++++++++++++++
>  3 files changed, 103 insertions(+)
> 
> diff --git a/include/uapi/linux/liveupdate.h b/include/uapi/linux/liveupdate.h
> index 30bc66ee9436a..41dc44d239dde 100644
> --- a/include/uapi/linux/liveupdate.h
> +++ b/include/uapi/linux/liveupdate.h
> @@ -59,6 +59,7 @@ enum {
>  	LIVEUPDATE_CMD_SESSION_PRESERVE_FD = LIVEUPDATE_CMD_SESSION_BASE,
>  	LIVEUPDATE_CMD_SESSION_RETRIEVE_FD = 0x41,
>  	LIVEUPDATE_CMD_SESSION_FINISH = 0x42,
> +	LIVEUPDATE_CMD_SESSION_GET_NAME = 0x43,
>  };
>  
>  /**
> @@ -213,4 +214,22 @@ struct liveupdate_session_finish {
>  #define LIVEUPDATE_SESSION_FINISH					\
>  	_IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_SESSION_FINISH)
>  
> +/**
> + * struct liveupdate_session_get_name - ioctl(LIVEUPDATE_SESSION_GET_NAME)
> + * @size:  Input; sizeof(struct liveupdate_session_get_name)
> + * @name:  Output; A null-terminated string with the full session name.
> + *
> + * Retrieves the full name of the session associated with this file descriptor.
> + * This is useful because the kernel may truncate the name shown in /proc.
> + *
> + * Return: 0 on success, negative error code on failure.
> + */
> +struct liveupdate_session_get_name {
> +	__u32		size;
> +	__u8		name[LIVEUPDATE_SESSION_NAME_LENGTH];

Add __u32  reserved;

Thanks,
Pasha


> +};
> +
> +#define LIVEUPDATE_SESSION_GET_NAME					\
> +	_IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_SESSION_GET_NAME)
> +
>  #endif /* _UAPI_LIVEUPDATE_H */
> diff --git a/kernel/liveupdate/luo_session.c b/kernel/liveupdate/luo_session.c
> index 25ae704d77873..af9e498206d24 100644
> --- a/kernel/liveupdate/luo_session.c
> +++ b/kernel/liveupdate/luo_session.c
> @@ -289,10 +289,21 @@ static int luo_session_finish(struct luo_session *session,
>  	return luo_ucmd_respond(ucmd, sizeof(*argp));
>  }
>  
> +static int luo_session_get_name(struct luo_session *session,
> +				struct luo_ucmd *ucmd)
> +{
> +	struct liveupdate_session_get_name *argp = ucmd->cmd;
> +
> +	strscpy((char *)argp->name, session->name, sizeof(argp->name));
> +
> +	return luo_ucmd_respond(ucmd, sizeof(*argp));
> +}
> +
>  union ucmd_buffer {
>  	struct liveupdate_session_finish finish;
>  	struct liveupdate_session_preserve_fd preserve;
>  	struct liveupdate_session_retrieve_fd retrieve;
> +	struct liveupdate_session_get_name get_name;
>  };
>  
>  struct luo_ioctl_op {
> @@ -319,6 +330,8 @@ static const struct luo_ioctl_op luo_session_ioctl_ops[] = {
>  		 struct liveupdate_session_preserve_fd, token),
>  	IOCTL_OP(LIVEUPDATE_SESSION_RETRIEVE_FD, luo_session_retrieve_fd,
>  		 struct liveupdate_session_retrieve_fd, token),
> +	IOCTL_OP(LIVEUPDATE_SESSION_GET_NAME, luo_session_get_name,
> +		 struct liveupdate_session_get_name, name),
>  };
>  
>  static long luo_session_ioctl(struct file *filep, unsigned int cmd,
> diff --git a/tools/testing/selftests/liveupdate/liveupdate.c b/tools/testing/selftests/liveupdate/liveupdate.c
> index c2878e3d5ef90..bdc1cedc4f944 100644
> --- a/tools/testing/selftests/liveupdate/liveupdate.c
> +++ b/tools/testing/selftests/liveupdate/liveupdate.c
> @@ -102,6 +102,22 @@ static int create_session(int lu_fd, const char *name)
>  	return args.fd;
>  }
>  
> +/* Helper function to get a session name via ioctl. */
> +static int get_session_name(int session_fd, char *name, size_t name_len)
> +{
> +	struct liveupdate_session_get_name args = {};
> +
> +	args.size = sizeof(args);
> +
> +	if (ioctl(session_fd, LIVEUPDATE_SESSION_GET_NAME, &args))
> +		return -errno;
> +
> +	strncpy(name, (char *)args.name, name_len - 1);
> +	name[name_len - 1] = '\0';
> +
> +	return 0;
> +}
> +
>  /*
>   * Test Case: Create Duplicate Session
>   *
> @@ -345,4 +361,59 @@ TEST_F(liveupdate_device, preserve_unsupported_fd)
>  	ASSERT_EQ(close(session_fd), 0);
>  }
>  
> +/*
> + * Test Case: Get Session Name
> + *
> + * Verifies that the full session name can be retrieved from a session file
> + * descriptor via ioctl.
> + */
> +TEST_F(liveupdate_device, get_session_name)
> +{
> +	char name_buf[LIVEUPDATE_SESSION_NAME_LENGTH] = {};
> +	const char *session_name = "get-name-test-session";
> +	int session_fd;
> +
> +	self->fd1 = open(LIVEUPDATE_DEV, O_RDWR);
> +	if (self->fd1 < 0 && errno == ENOENT)
> +		SKIP(return, "%s does not exist", LIVEUPDATE_DEV);
> +	ASSERT_GE(self->fd1, 0);
> +
> +	session_fd = create_session(self->fd1, session_name);
> +	ASSERT_GE(session_fd, 0);
> +
> +	ASSERT_EQ(get_session_name(session_fd, name_buf, sizeof(name_buf)), 0);
> +	ASSERT_STREQ(name_buf, session_name);
> +
> +	ASSERT_EQ(close(session_fd), 0);
> +}
> +
> +/*
> + * Test Case: Get Session Name at Maximum Length
> + *
> + * Verifies that a session name using the full LIVEUPDATE_SESSION_NAME_LENGTH
> + * (minus the null terminator) can be correctly retrieved.
> + */
> +TEST_F(liveupdate_device, get_session_name_max_length)
> +{
> +	char name_buf[LIVEUPDATE_SESSION_NAME_LENGTH] = {};
> +	char long_name[LIVEUPDATE_SESSION_NAME_LENGTH];
> +	int session_fd;
> +
> +	memset(long_name, 'A', sizeof(long_name) - 1);
> +	long_name[sizeof(long_name) - 1] = '\0';
> +
> +	self->fd1 = open(LIVEUPDATE_DEV, O_RDWR);
> +	if (self->fd1 < 0 && errno == ENOENT)
> +		SKIP(return, "%s does not exist", LIVEUPDATE_DEV);
> +	ASSERT_GE(self->fd1, 0);
> +
> +	session_fd = create_session(self->fd1, long_name);
> +	ASSERT_GE(session_fd, 0);
> +
> +	ASSERT_EQ(get_session_name(session_fd, name_buf, sizeof(name_buf)), 0);
> +	ASSERT_STREQ(name_buf, long_name);
> +
> +	ASSERT_EQ(close(session_fd), 0);
> +}
> +
>  TEST_HARNESS_MAIN
> -- 
> 2.47.3
>