linux-kernel - Re: [PATCH 3/4] configfs: implement committable items

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Message-ID: <X/+GQIhGmyHlIe0+@google.com>
Date:   Wed, 13 Jan 2021 15:46:08 -0800
From:   Joel Becker <jlbec@...lplan.org>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH 3/4] configfs: implement committable items

On Wed, Nov 25, 2020 at 04:22:46PM +0100, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> 
> This implements configfs committable items. We mostly follow the
> documentation except that we extend config_group_ops with uncommit_item()
> callback for reverting the changes made by commit_item().

Woohoo!  A long time coming, but thank you for working on the
implementation!

> Each committable group has two sub-directories: pending and live. New
> items can only be created in pending/. Attributes can only be modified
> while the item is in pending/. Once it's ready to be committed, it must
> be moved over to live/ using the rename() system call. This is when the
> commit_item() function will be called.

The original API intended for live items to still be modifyable.  The
live/ path forbids mkdir()/rmdir(), but it allows store().  Otherwise,
items can't be adjusted at all while in use, which is severely limiting.
Obviously the store() handler must not allow transitions from
valid-value->invalid-value, but the handler would reject invalid values
anyway, wouldn't it?

> diff --git a/fs/configfs/file.c b/fs/configfs/file.c
> index 1f0270229d7b..a20e55fd05e8 100644
> --- a/fs/configfs/file.c
> +++ b/fs/configfs/file.c
> @@ -243,9 +243,17 @@ fill_write_buffer(struct configfs_buffer * buffer, const char __user * buf, size
>  static int
>  flush_write_buffer(struct file *file, struct configfs_buffer *buffer, size_t count)
>  {
> +	struct config_item *parent_item = buffer->item->ci_parent;
>  	struct configfs_fragment *frag = to_frag(file);
> +	struct configfs_dirent *sd;
>  	int res = -ENOENT;
>  
> +	if (parent_item && parent_item->ci_dentry) {
> +		sd = parent_item->ci_dentry->d_fsdata;
> +		if (sd->s_type & CONFIGFS_GROUP_LIVE)
> +			return -EPERM;
> +	}
> +
>  	down_read(&frag->frag_sem);
>  	if (!frag->frag_dead)
>  		res = buffer->attr->store(buffer->item, buffer->page, count);

Basically, I would just leave this hunk out.

Thanks,
Joel

-- 

"Now Someone's on the telephone, desperate in his pain.
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			http://www.jlbec.org/
			jlbec@...lplan.org