linux-kernel - Re: [PATCH] net/socket: set socket inode times to current

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Message-ID: <20230202204224.9668-1-kuniyu@amazon.com>
Date:   Thu, 2 Feb 2023 12:42:24 -0800
From:   Kuniyuki Iwashima <kuniyu@...zon.com>
To:     <whzhao@...il.com>
CC:     <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        <pabeni@...hat.com>
Subject: Re: [PATCH] net/socket: set socket inode times to current_time

From:   Wenhua Zhao <whzhao@...il.com>
Date:   Tue, 31 Jan 2023 20:30:19 -0800
> Socket creation time are sometimes useful but not available becasue the
> socket inode times are not set when initializing the inode.  This patch
> sets the socket inode times to current_time().
> 
> Before the fix, the socket inode times are at epoch, for example:
> 
>     $ stat -L /proc/383/fd/3
>       File: /proc/383/fd/3
>       Size: 0               Blocks: 0          IO Block: 4096   socket
>     Device: 0,8     Inode: 15996       Links: 1
>     Access: (0777/srwxrwxrwx)  Uid: ( 1000/    arch)   Gid: ( 1000/    arch)
>     Access: 1970-01-01 00:00:00.000000000 +0000
>     Modify: 1970-01-01 00:00:00.000000000 +0000
>     Change: 1970-01-01 00:00:00.000000000 +0000
> 
> After the fix, the inode times are the socket creation time:
> 
>     $ stat -L /proc/254/fd/3
>       File: /proc/254/fd/3
>       Size: 0               Blocks: 0          IO Block: 4096   socket
>     Device: 0,7     Inode: 13170       Links: 1
>     Access: (0777/srwxrwxrwx)  Uid: ( 1000/    arch)   Gid: ( 1000/    arch)
>     Access: 2023-02-01 03:27:50.094731201 +0000
>     Modify: 2023-02-01 03:27:50.094731201 +0000
>     Change: 2023-02-01 03:27:50.094731201 +0000
> 
> Signed-off-by: Wenhua Zhao <whzhao@...il.com>

Looks good, but we may want to use another example in changelog
because you can get almost the same time without the -L option
and the use case is bit confusing at least for me.

I guess you will use it in your application, not from the outside
world by stat.

  $ python3
  >>> from socket import socket
  >>> from os import fstat
  >>> 
  >>> sk = socket()
  >>> fstat(sk.fileno())
  os.stat_result(..., st_atime=0, st_mtime=0, st_ctime=0)


> ---
>  net/socket.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/socket.c b/net/socket.c
> index 888cd618a968..c656c9599a92 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -635,6 +635,7 @@ struct socket *sock_alloc(void)
>  	inode->i_uid = current_fsuid();
>  	inode->i_gid = current_fsgid();
>  	inode->i_op = &sockfs_inode_ops;
> +	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
>  
>  	return sock;
>  }
> -- 
> 2.39.1