Re: [PATCH] vhost_net: Use fdget() and fdput()

Re: [PATCH] vhost_net: Use fdget() and fdput()

[Jason Wang]

On Fri, May 5, 2023 at 2:24 PM <ye.xingchen@zte.com.cn> wrote:
>
> From: Ye Xingchen <ye.xingchen@zte.com.cn>
>
> convert the fget()/fput() uses to fdget()/fdput().

What's the advantages of this?

Thanks

>
> Signed-off-by: Ye Xingchen <ye.xingchen@zte.com.cn>
> ---
>  drivers/vhost/net.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index ae2273196b0c..5b3fe4805182 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -1466,17 +1466,17 @@ static struct ptr_ring *get_tap_ptr_ring(struct file *file)
>
>  static struct socket *get_tap_socket(int fd)
>  {
> -       struct file *file = fget(fd);
> +       struct fd f = fdget(fd);
>         struct socket *sock;
>
> -       if (!file)
> +       if (!f.file)
>                 return ERR_PTR(-EBADF);
> -       sock = tun_get_socket(file);
> +       sock = tun_get_socket(f.file);
>         if (!IS_ERR(sock))
>                 return sock;
> -       sock = tap_get_socket(file);
> +       sock = tap_get_socket(f.file);
>         if (IS_ERR(sock))
> -               fput(file);
> +               fdput(f);
>         return sock;
>  }
>
> --
> 2.25.1
>

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Re: [PATCH] vhost_net: Use fdget() and fdput()

[Michael S. Tsirkin]

On Fri, May 05, 2023 at 04:41:55PM +0800, ye xingchen wrote:
> >>
> >> From: Ye Xingchen <ye.xingchen@zte.com.cn>
> >>
> >> convert the fget()/fput() uses to fdget()/fdput().
> >What's the advantages of this?
> >
> >Thanks
> >>
> >> Signed-off-by: Ye Xingchen <ye.xingchen@zte.com.cn>
> >> ---
> >>  drivers/vhost/net.c | 10 +++++-----
> >>  1 file changed, 5 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> >> index ae2273196b0c..5b3fe4805182 100644
> >> --- a/drivers/vhost/net.c
> >> +++ b/drivers/vhost/net.c
> >> @@ -1466,17 +1466,17 @@ static struct ptr_ring *get_tap_ptr_ring(struct file *file)
> >>
> >>  static struct socket *get_tap_socket(int fd)
> >>  {
> >> -       struct file *file = fget(fd);
> >> +       struct fd f = fdget(fd);
> >>         struct socket *sock;
> >>
> >> -       if (!file)
> >> +       if (!f.file)
> >>                 return ERR_PTR(-EBADF);
> >> -       sock = tun_get_socket(file);
> >> +       sock = tun_get_socket(f.file);
> >>         if (!IS_ERR(sock))
> >>                 return sock;
> >> -       sock = tap_get_socket(file);
> >> +       sock = tap_get_socket(f.file);
> >>         if (IS_ERR(sock))
> >> -               fput(file);
> >> +               fdput(f);
> >>         return sock;
> >>  }
> >>
> >> --
> >> 2.25.1
> >>
> fdget requires an integer type file descriptor as its parameter, 
> and fget requires a pointer to the file structure as its parameter.

In which kernel?

include/linux/file.h:extern struct file *fget(unsigned int fd);


> By using the fdget function, the socket object, can be quickly 
> obtained from the process's file descriptor table without 
> the need to obtain the file descriptor first before passing it 
> as a parameter to the fget function. This reduces unnecessary 
> operations, improves system efficiency and performance.
> 
> Best Regards
> Ye

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Re: [PATCH] vhost_net: Use fdget() and fdput()

[Al Viro]

On Fri, May 05, 2023 at 02:24:04PM +0800, ye.xingchen@zte.com.cn wrote:
> From: Ye Xingchen <ye.xingchen@zte.com.cn>
> 
> convert the fget()/fput() uses to fdget()/fdput().
> 
> Signed-off-by: Ye Xingchen <ye.xingchen@zte.com.cn>
> ---
>  drivers/vhost/net.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index ae2273196b0c..5b3fe4805182 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -1466,17 +1466,17 @@ static struct ptr_ring *get_tap_ptr_ring(struct file *file)
> 
>  static struct socket *get_tap_socket(int fd)
>  {
> -	struct file *file = fget(fd);
> +	struct fd f = fdget(fd);
>  	struct socket *sock;
> 
> -	if (!file)
> +	if (!f.file)
>  		return ERR_PTR(-EBADF);
> -	sock = tun_get_socket(file);
> +	sock = tun_get_socket(f.file);
>  	if (!IS_ERR(sock))
>  		return sock;
> -	sock = tap_get_socket(file);
> +	sock = tap_get_socket(f.file);
>  	if (IS_ERR(sock))
> -		fput(file);
> +		fdput(f);
>  	return sock;

NAK.  For the same reason why the sockfd_lookup() counterpart of that
patch is broken.  After your change there's no way for the caller
to tell whether we have bumped the refcount of file in question;
this can't possibly work.
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