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SubjectRe: [PATCH net-next 1/2] socket: Allow external sockets to use socket syscalls

On 12/26/2014 02:50 PM, Alex Gartrell wrote:
> Currently the "is-socket" test for a file compares the ops table pointer,
> which is static and local to the socket.c. Instead, this adds a flag for
> private_data_is_socket. This is an exceptionally long commit message for a
> two-line patch.
>
> Signed-off-by: Alex Gartrell <agartrell@fb.com>
> ---
> include/linux/fs.h | 2 +-
> net/socket.c | 3 ++-
> 2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index bb29b02..d162476 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -809,7 +809,7 @@ struct file {
> #endif
> /* needed for tty driver, and maybe others */
> void *private_data;
> -
> + bool private_data_is_socket : 1;
> #ifdef CONFIG_EPOLL
> /* Used by fs/eventpoll.c to link all the hooks to this file */
> struct list_head f_ep_links;
> diff --git a/net/socket.c b/net/socket.c
> index 8809afc..cd853be 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -388,6 +388,7 @@ struct file *sock_alloc_file(struct socket *sock, int flags, const char *dname)
> sock->file = file;
> file->f_flags = O_RDWR | (flags & O_NONBLOCK);
> file->private_data = sock;
> + file->private_data_is_socket = true;

This is only safe if all user of sock_alloc_file() have full support for
each method in proto_ops.
> return file;
> }
> EXPORT_SYMBOL(sock_alloc_file);
> @@ -411,7 +412,7 @@ static int sock_map_fd(struct socket *sock, int flags)
>
> struct socket *sock_from_file(struct file *file, int *err)
> {
> - if (file->f_op == &socket_file_ops)
> + if (file->private_data_is_socket)
> return file->private_data; /* set in sock_map_fd */
>
> *err = -ENOTSOCK;

Not sure it's the best method, how about a dedicated f_op to do this?


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