linux-kernel - Re: [PATCH v3 18/30] liveupdate: luo_files: luo_ioctl: Add ioctls for per-file state management

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Message-ID: <20250814140252.GF802098@nvidia.com>
Date: Thu, 14 Aug 2025 11:02:52 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Pasha Tatashin <pasha.tatashin@...een.com>
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Subject: Re: [PATCH v3 18/30] liveupdate: luo_files: luo_ioctl: Add ioctls
 for per-file state management

On Thu, Aug 07, 2025 at 01:44:24AM +0000, Pasha Tatashin wrote:
> +struct liveupdate_ioctl_get_fd_state {
> +	__u32		size;
> +	__u8		incoming;
> +	__aligned_u64	token;
> +	__u32		state;
> +};

Same remark about explicit padding and checking padding for 0

> + * luo_file_get_state - Get the preservation state of a specific file.
> + * @token: The token of the file to query.
> + * @statep: Output pointer to store the file's current live update state.
> + * @incoming: If true, query the state of a restored file from the incoming
> + *            (previous kernel's) set. If false, query a file being prepared
> + *            for preservation in the current set.
> + *
> + * Finds the file associated with the given @token in either the incoming
> + * or outgoing tracking arrays and returns its current LUO state
> + * (NORMAL, PREPARED, FROZEN, UPDATED).
> + *
> + * Return: 0 on success, -ENOENT if the token is not found.
> + */
> +int luo_file_get_state(u64 token, enum liveupdate_state *statep, bool incoming)
> +{
> +	struct luo_file *luo_file;
> +	struct xarray *target_xa;
> +	int ret = 0;
> +
> +	luo_state_read_enter();

Less globals, at this point everything should be within memory
attached to the file descriptor and not in globals. Doing this will
promote good maintainable structure and not a spaghetti

Also I think a BKL design is not a good idea for new code. We've had
so many bad experiences with this pattern promoting uncontrolled
incomprehensible locking.

The xarray already has a lock, why not have reasonable locking inside
the luo_file? Probably just a refcount?

> +	target_xa = incoming ? &luo_files_xa_in : &luo_files_xa_out;
> +	luo_file = xa_load(target_xa, token);
> +
> +	if (!luo_file) {
> +		ret = -ENOENT;
> +		goto out_unlock;
> +	}
> +
> +	scoped_guard(mutex, &luo_file->mutex)
> +		*statep = luo_file->state;
> +
> +out_unlock:
> +	luo_state_read_exit();

If we are using cleanup.h then use it for this too..

But it seems kind of weird, why not just

xa_lock()
xa_load()
*statep = READ_ONCE(luo_file->state);
xa_unlock()

?

> +static int luo_ioctl_set_fd_event(struct luo_ucmd *ucmd)
> +{
> +	struct liveupdate_ioctl_set_fd_event *argp = ucmd->cmd;
> +	int ret;
> +
> +	switch (argp->event) {
> +	case LIVEUPDATE_PREPARE:
> +		ret = luo_file_prepare(argp->token);
> +		break;
> +	case LIVEUPDATE_FREEZE:
> +		ret = luo_file_freeze(argp->token);
> +		break;
> +	case LIVEUPDATE_FINISH:
> +		ret = luo_file_finish(argp->token);
> +		break;
> +	case LIVEUPDATE_CANCEL:
> +		ret = luo_file_cancel(argp->token);
> +		break;

The token should be converted to a file here instead of duplicated in
each function

>  static int luo_open(struct inode *inodep, struct file *filep)
>  {
>  	if (atomic_cmpxchg(&luo_device_in_use, 0, 1))
> @@ -149,6 +191,8 @@ union ucmd_buffer {
>  	struct liveupdate_ioctl_fd_restore	restore;
>  	struct liveupdate_ioctl_get_state	state;
>  	struct liveupdate_ioctl_set_event	event;
> +	struct liveupdate_ioctl_get_fd_state	fd_state;
> +	struct liveupdate_ioctl_set_fd_event	fd_event;
>  };
>  
>  struct luo_ioctl_op {
> @@ -179,6 +223,10 @@ static const struct luo_ioctl_op luo_ioctl_ops[] = {
>  		 struct liveupdate_ioctl_get_state, state),
>  	IOCTL_OP(LIVEUPDATE_IOCTL_SET_EVENT, luo_ioctl_set_event,
>  		 struct liveupdate_ioctl_set_event, event),
> +	IOCTL_OP(LIVEUPDATE_IOCTL_GET_FD_STATE, luo_ioctl_get_fd_state,
> +		 struct liveupdate_ioctl_get_fd_state, token),
> +	IOCTL_OP(LIVEUPDATE_IOCTL_SET_FD_EVENT, luo_ioctl_set_fd_event,
> +		 struct liveupdate_ioctl_set_fd_event, token),
>  };

Keep sorted

Jason