Re: [PATCH] configfs: implement binary attributes

Joel Becker
2015-12-29T23:00:47Z

On Thu, Dec 24, 2015 at 03:51:10PM +0100, Christoph Hellwig wrote:
> From: Pantelis Antoniou <pantelis.antoniou@konsulko.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

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