[PATCH v9 3/6] liveupdate: add LUO_SESSION_MAGIC magic inode type

[Mike Rapoport]

On Mon, Apr 20, 2026 at 03:15:11PM +0100, luca.boccassi at gmail.com wrote:
> From: Luca Boccassi <luca.boccassi at gmail.com>
> 
> In userspace when managing LUO sessions we want to be able to identify
> a FD as a LUO session, in order to be able to do the special handling
> that they require in order to function as intended on kexec.
> 
> Currently this requires scraping procfs and doing string matching on
> the prefix of the dname, which is not an ideal interface.
> 
> Add a singleton inode type with a magic value, so that we can
> programmatically identify a fd as a LUO session via fstatfs().
> 
> Signed-off-by: Luca Boccassi <luca.boccassi at gmail.com>
> Reviewed-by: Pasha Tatashin <pasha.tatashin at soleen.com>
> ---
>  include/uapi/linux/magic.h       |  1 +
>  kernel/liveupdate/luo_core.c     | 10 +++-
>  kernel/liveupdate/luo_internal.h |  2 +
>  kernel/liveupdate/luo_session.c  | 91 ++++++++++++++++++++++++++++++--
>  4 files changed, 98 insertions(+), 6 deletions(-)
> 
> diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
> index 4f2da935a76c..4f51005522ff 100644
> --- a/include/uapi/linux/magic.h
> +++ b/include/uapi/linux/magic.h
> @@ -105,5 +105,6 @@
>  #define PID_FS_MAGIC		0x50494446	/* "PIDF" */
>  #define GUEST_MEMFD_MAGIC	0x474d454d	/* "GMEM" */
>  #define NULL_FS_MAGIC		0x4E554C4C	/* "NULL" */
> +#define LUO_SESSION_MAGIC	0x4c554f53	/* "LUOS" */
>  
>  #endif /* __LINUX_MAGIC_H__ */
> diff --git a/kernel/liveupdate/luo_core.c b/kernel/liveupdate/luo_core.c
> index dda7bb57d421..f1a63ebe4fa4 100644
> --- a/kernel/liveupdate/luo_core.c
> +++ b/kernel/liveupdate/luo_core.c
> @@ -197,9 +197,17 @@ static int __init luo_late_startup(void)
>  	if (!liveupdate_enabled())
>  		return 0;
>  
> +	err = luo_session_fs_init();
> +	if (err) {
> +		luo_global.enabled = false;

Please use goto here and on luo_fdt_setup() failure to handle cleanup on error.

Other than that

Acked-by: Mike Rapoport (Microsoft) <rppt at kernel.org>


> +		return err;
> +	}
> +
>  	err = luo_fdt_setup();
> -	if (err)
> +	if (err) {
> +		luo_session_fs_cleanup();
>  		luo_global.enabled = false;
> +	}
>  
>  	return err;
>  }

-- 
Sincerely yours,
Mike.