Re: [PATCH 2/4] fs: add pread and pwrite functions

[Sascha Hauer <s.hauer@pengutronix.de>]

On Thu, Feb 14, 2013 at 02:08:29PM +0100, Alexander Aring wrote:
> Add pread and pwrite functions.
> 
> These functions setting file pointer to a given
> offset with lseek and call read or write afterwards.
> 
> Signed-off-by: Alexander Aring <alex.aring@gmail.com>
> ---
>  fs/fs.c      | 28 ++++++++++++++++++++++++++++
>  include/fs.h |  2 ++
>  2 files changed, 30 insertions(+)
> 
> diff --git a/fs/fs.c b/fs/fs.c
> index 48d1c89..fea7e02 100644
> --- a/fs/fs.c
> +++ b/fs/fs.c
> @@ -785,6 +785,20 @@ ssize_t read(int fd, void *buf, size_t count)
>  }
>  EXPORT_SYMBOL(read);
>  
> +ssize_t pread(int fd, void *buf, size_t count, loff_t offset)
> +{
> +	int ret;
> +
> +	ret = lseek(fd, offset, SEEK_SET);
> +	if (ret < 0)
> +		goto out;
> +
> +	ret = read(fd, buf, count);
> +out:
> +	return ret;
> +}

The man page says that the file offset is not modified by pread/pwrite.
If we add a standard function with a standard prototype I think it
should have the same behaviour.
Maybe this can be implemented similar to the current read() function
is implemented. read() could then call pread() internally and advances
the file offset afterwards.

Sascha


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