Subject: Re: [PATCH] configfs: implement binary attributes
To: Christoph Hellwig <hch@lst.de>, akpm@linux-foundation.org,
        nab@linux-iscsi.org, pantelis.antoniou@konsulko.com,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
References: <1450968671-13699-1-git-send-email-hch@lst.de>
 <1450968671-13699-2-git-send-email-hch@lst.de>
 <20151229230029.GC32415@noexit.roam.corp.google.com>
From: Krzysztof Opasiak <k.opasiak@samsung.com>
Message-id: <568316B1.6090800@samsung.com>
Date: Wed, 30 Dec 2015 00:26:41 +0100
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W dniu 2015-12-30 o 00:00, Joel Becker pisze:
 > 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
 >

I think that static inline helper can be usefull here to improve readability

 >> +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
 >

-- 
Krzysztof Opasiak
Samsung R&D Institute Poland
Samsung Electronics
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