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

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Date:   Fri, 5 May 2023 10:59:37 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     ye xingchen <yexingchen116@...il.com>
Cc:     jasowang@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, ye.xingchen@....com.cn
Subject: Re: [PATCH] vhost_net: Use fdget() and fdput()

On Fri, May 05, 2023 at 04:41:55PM +0800, ye xingchen wrote:
> >>
> >> From: Ye Xingchen <ye.xingchen@....com.cn>
> >>
> >> convert the fget()/fput() uses to fdget()/fdput().
> >What's the advantages of this?
> >
> >Thanks
> >>
> >> Signed-off-by: Ye Xingchen <ye.xingchen@....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