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Date: Fri, 5 Aug 2005 00:57:53 -0700
From: Andrew Morton <akpm@osdl.org>
To: Tom Zanussi <zanussi@us.ibm.com>
Cc: linux-kernel@vger.kernel.org, karim@opersys.com, prasadav@us.ibm.com
Subject: Re: [-mm patch] relayfs: add read() support
Message-Id: <20050805005753.031db798.akpm@osdl.org>
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Tom Zanussi <zanussi@us.ibm.com> wrote:
>
> +static ssize_t relayfs_read(struct file *filp,
>  +			    char __user *buffer,
>  +			    size_t count,
>  +			    loff_t *ppos)
>  +{
>  +	struct inode *inode = filp->f_dentry->d_inode;
>  +	struct rchan_buf *buf = RELAYFS_I(inode)->buf;
>  +	unsigned int read_start, read_end, avail, start_subbuf;
>  +	unsigned int buf_size = buf->chan->subbuf_size * buf->chan->n_subbufs;
>  +	void *from;
>  +
>  +	avail = relayfs_read_avail(buf, &start_subbuf);
>  +	if (*ppos >= avail)
>  +		return 0;
>  +
>  +	read_start = relayfs_read_start(*ppos, avail, start_subbuf, buf);
>  +	if (read_start == 0 && *ppos)
>  +		return 0;
>  +	
>  +	read_end = relayfs_read_end(read_start, avail, start_subbuf, buf);
>  +	if (read_end == read_start)
>  +		return 0;
>  +	
>  +	from = buf->start + start_subbuf * buf->chan->subbuf_size + read_start;
>  +	if (from >= buf->start + buf_size)
>  +		from -= buf_size;
>  +
>  +	count = min(count, read_end - read_start);
>  +	if (copy_to_user(buffer, from, count))
>  +		return -EFAULT;
>  +
>  +	*ppos = read_start + count;
>  +	
>  +	return count;
>  +}

The use of `unsigned int' in here will cause >4G reads to fail on 64-bit
platforms.  I think you want size_t throughout.