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

Joel Becker
2021-01-14T01:56:27Z

On Wed, Nov 25, 2020 at 04:22:46PM +0100, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@baylibre.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

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