Re: [RFC] liveupdate: prevent double preservation

[Jan Kara <jack@suse.cz>]

On Mon 16-03-26 22:38:34, Pasha Tatashin wrote:
> Currently, LUO does not prevent the same file from being preserved twice
> across different active sessions.
> 
> Add a new i_state flag I_LUO_PRESERVED and update luo_preserve_file()
> to check and set this flag when a file is preserved, and clear it in
> luo_file_unpreserve_files() when it is released. This ensures that the
> same file (inode) cannot be preserved by multiple sessions. If another
> session attempts to preserve an already preserved file, it will now
> fail with -EBUSY.
> 
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
> 
> Background:
> Because LUO preserves files of absolutely different types: memfd, and
> upcoming  vfiofd [1], iommufd [2], guestmefd (and possible kvmfd/cpufd).
> There is no common private data or guarantee on how to prevent that the
> same file is not preserved twice beside using inode or some slower and
> expensive method like hashtables.

OK, I guess since this is a single bit, we can live with that although it
seems a bit wrong that LUO needs this in generic struct inode. But all
other "cleaner" variants I could think of were just an overkill. So feel
free to add:

Acked-by: Jan Kara <jack@suse.cz>

Just one nit below:

> [1] https://lore.kernel.org/all/20260129212510.967611-1-dmatlack@google.com
> [2] https://lore.kernel.org/all/20260203220948.2176157-1-skhawaja@google.com
> 
> @@ -744,7 +746,8 @@ enum inode_state_flags_enum {
>  	I_CREATING		= (1U << 15),
>  	I_DONTCACHE		= (1U << 16),
>  	I_SYNC_QUEUED		= (1U << 17),
> -	I_PINNING_NETFS_WB	= (1U << 18)
> +	I_PINNING_NETFS_WB	= (1U << 18),
> +	I_LUO_PRESERVED		= (1U << 19)

Add comma at the end of line here please so that we don't have to modify
the last line again.

								Honza

-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR