linux-kernel - Re: [PATCH] configfs: implement binary attributes

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Date:	Tue, 29 Dec 2015 15:00:30 -0800
From:	Joel Becker <jlbec@...lplan.org>
To:	Christoph Hellwig <hch@....de>
Cc:	akpm@...ux-foundation.org, nab@...ux-iscsi.org,
	pantelis.antoniou@...sulko.com, k.opasiak@...sung.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] configfs: implement binary attributes

On Thu, Dec 24, 2015 at 03:51:10PM +0100, Christoph Hellwig wrote:
> From: Pantelis Antoniou <pantelis.antoniou@...sulko.com>
> 
> ConfigFS lacked binary attributes up until now. This patch
> introduces support for binary attributes in a somewhat similar
> manner of sysfs binary attributes albeit with changes that
> fit the configfs usage model.
> 
> Problems that configfs binary attributes fix are everything that
> requires a binary blob as part of the configuration of a resource,
> such as bitstream loading for FPGAs, DTBs for dynamically created
> devices etc.

Overall, I really like this addition.

> @@ -423,7 +429,9 @@ static int configfs_attach_attr(struct configfs_dirent * sd, struct dentry * den
>  	spin_unlock(&configfs_dirent_lock);
>  
>  	error = configfs_create(dentry, (attr->ca_mode & S_IALLUGO) | S_IFREG,
> -				configfs_init_file);
> +				(sd->s_type & CONFIGFS_ITEM_ATTR) ?
> +					configfs_init_file :
> +					configfs_init_bin_file);

BIN_ATTRs are the more uncommon type, at least for now.  I would think
this code should check for special cases and fall back to ITEM_ATTR.  So
reverse it.

	(sd->s_type & CONFIGFS_ITEM_BIN_ATTR) ?
  		configfs_init_bin_file :
		configfs_init_file

> +static ssize_t
> +configfs_read_bin_file(struct file *file, char __user *buf,
> +		       size_t count, loff_t *ppos)
> +{
> +	struct configfs_buffer *buffer = file->private_data;
> +	struct dentry *dentry = file->f_path.dentry;
> +	struct config_item *item = to_item(dentry->d_parent);
> +	struct configfs_bin_attribute *bin_attr = to_bin_attr(dentry);
> +	ssize_t retval = 0;
> +	ssize_t len = min_t(size_t, count, PAGE_SIZE);
> +
> +	mutex_lock(&buffer->mutex);
> +
> +	/* we don't support switching read/write modes */
> +	if (buffer->write_in_progress) {
> +		retval = -EINVAL;
> +		goto out;
> +	}

These are valid arguments, it's just competing with another operation.
Wouldn't something like EINPROGRESS or ETXTBSY make more sense and be
more informative?  The same for configfs_write_bin_file().

Joel 

-- 

"Soap and education are not as sudden as a massacre, but they are more
 deadly in the long run."
	- Mark Twain


			http://www.jlbec.org/
			jlbec@...lplan.org
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