linux-kernel - Re: [PATCH net-next v4 3/3] eventpoll: Add epoll ioctl for epoll

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Date: Wed, 31 Jan 2024 07:03:54 +0100
From: Jiri Slaby <jirislaby@...nel.org>
To: Joe Damato <jdamato@...tly.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
 chuck.lever@...cle.com, jlayton@...nel.org, linux-api@...r.kernel.org,
 brauner@...nel.org, edumazet@...gle.com, davem@...emloft.net,
 alexander.duyck@...il.com, sridhar.samudrala@...el.com, kuba@...nel.org,
 willemdebruijn.kernel@...il.com, weiwan@...gle.com, David.Laight@...lab.com,
 arnd@...db.de, Jonathan Corbet <corbet@....net>,
 Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
 Michael Ellerman <mpe@...erman.id.au>, Nathan Lynch <nathanl@...ux.ibm.com>,
 Thomas Zimmermann <tzimmermann@...e.de>, Maik Broemme <mbroemme@...mpq.org>,
 Steve French <stfrench@...rosoft.com>, Julien Panis <jpanis@...libre.com>,
 Thomas Huth <thuth@...hat.com>, Andrew Waterman
 <waterman@...s.berkeley.edu>, Albert Ou <aou@...s.berkeley.edu>,
 Palmer Dabbelt <palmer@...belt.com>,
 "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
 "open list:FILESYSTEMS (VFS and infrastructure)"
 <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH net-next v4 3/3] eventpoll: Add epoll ioctl for
 epoll_params

On 31. 01. 24, 3:27, Joe Damato wrote:
> On Tue, Jan 30, 2024 at 06:08:36PM -0800, Greg Kroah-Hartman wrote:
>> On Wed, Jan 31, 2024 at 01:47:33AM +0000, Joe Damato wrote:
>>> +struct epoll_params {
>>> +	__aligned_u64 busy_poll_usecs;
>>> +	__u16 busy_poll_budget;
>>> +
>>> +	/* pad the struct to a multiple of 64bits for alignment on all arches */
>>> +	__u8 __pad[6];
>>
>> You HAVE to check this padding to be sure it is all 0, otherwise it can
>> never be used in the future for anything.
> 
> Is there some preferred mechanism for this in the kernel that I should be
> using or is this as simple as adding a for loop to check each u8 == 0 ?

You are likely looking for memchr_inv().

-- 
js
suse labs