linux-kernel - Re: [RFC 01/15] FS: libfs, implement simple_write_to

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Message-Id: <201003242313.36811.rjw@sisk.pl>
Date:	Wed, 24 Mar 2010 23:13:36 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	jirislaby@...il.com, pavel@....cz,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Nigel Cunningham <ncunningham@...a.org.au>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [RFC 01/15] FS: libfs, implement simple_write_to_buffer

On Tuesday 23 March 2010, Jiri Slaby wrote:
> It will be used in suspend code and serves as an easy wrap around
> copy_from_user. Similar to simple_read_from_buffer, it takes care
> of transfers with proper lengths depending on available and count
> parameters and advances ppos appropriately.
> 
> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
> Cc: Nigel Cunningham <ncunningham@...a.org.au>
> Cc: "Rafael J. Wysocki" <rjw@...k.pl>
> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> Cc: linux-fsdevel@...r.kernel.org

No objections from me.

Is there any concern from the fs side?

Rafael


> ---
>  fs/libfs.c         |   35 +++++++++++++++++++++++++++++++++++
>  include/linux/fs.h |    2 ++
>  2 files changed, 37 insertions(+), 0 deletions(-)
> 
> diff --git a/fs/libfs.c b/fs/libfs.c
> index 9e50bcf..fda73b3 100644
> --- a/fs/libfs.c
> +++ b/fs/libfs.c
> @@ -546,6 +546,40 @@ ssize_t simple_read_from_buffer(void __user *to, size_t count, loff_t *ppos,
>  }
>  
>  /**
> + * simple_write_to_buffer - copy data from user space to the buffer
> + * @to: the buffer to write to
> + * @available: the size of the buffer
> + * @ppos: the current position in the buffer
> + * @from: the user space buffer to read from
> + * @count: the maximum number of bytes to read
> + *
> + * The simple_write_to_buffer() function reads up to @count bytes from the user
> + * space address starting at @from into the buffer @to at offset @ppos.
> + *
> + * On success, the number of bytes written is returned and the offset @ppos is
> + * advanced by this number, or negative value is returned on error.
> + **/
> +ssize_t simple_write_to_buffer(void *to, size_t available, loff_t *ppos,
> +		const void __user *from, size_t count)
> +{
> +	loff_t pos = *ppos;
> +	size_t ret;
> +
> +	if (pos < 0)
> +		return -EINVAL;
> +	if (pos >= available || !count)
> +		return 0;
> +	if (count > available - pos)
> +		count = available - pos;
> +	ret = copy_from_user(to + pos, from, count);
> +	if (ret == count)
> +		return -EFAULT;
> +	count -= ret;
> +	*ppos = pos + count;
> +	return count;
> +}
> +
> +/**
>   * memory_read_from_buffer - copy data from the buffer
>   * @to: the kernel space buffer to read to
>   * @count: the maximum number of bytes to read
> @@ -863,6 +897,7 @@ EXPORT_SYMBOL(simple_statfs);
>  EXPORT_SYMBOL(simple_sync_file);
>  EXPORT_SYMBOL(simple_unlink);
>  EXPORT_SYMBOL(simple_read_from_buffer);
> +EXPORT_SYMBOL(simple_write_to_buffer);
>  EXPORT_SYMBOL(memory_read_from_buffer);
>  EXPORT_SYMBOL(simple_transaction_set);
>  EXPORT_SYMBOL(simple_transaction_get);
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index a4636b6..0f751b6 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2370,6 +2370,8 @@ extern void simple_release_fs(struct vfsmount **mount, int *count);
>  
>  extern ssize_t simple_read_from_buffer(void __user *to, size_t count,
>  			loff_t *ppos, const void *from, size_t available);
> +extern ssize_t simple_write_to_buffer(void *to, size_t available, loff_t *ppos,
> +		const void __user *from, size_t count);
>  
>  extern int simple_fsync(struct file *, struct dentry *, int);
>  
> 

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