public inbox for [email protected]
 help / color / mirror / Atom feed
From: Jens Axboe <[email protected]>
To: Pavel Begunkov <[email protected]>,
	Arnd Bergmann <[email protected]>,
	Greg Kroah-Hartman <[email protected]>,
	[email protected]
Cc: [email protected]
Subject: Re: [PATCH] /dev/mem: nowait zero/null ops
Date: Wed, 8 Sep 2021 06:57:09 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <16c78d25f507b571df7eb852a571141a0fdc73fd.1631095567.git.asml.silence@gmail.com>

On 9/8/21 4:06 AM, Pavel Begunkov wrote:
> Make read_iter_zero() to honor IOCB_NOWAIT, so /dev/zero can be
> advertised as FMODE_NOWAIT. This helps subsystems like io_uring to use
> it more effectively. Set FMODE_NOWAIT for /dev/null as well, it never
> waits and therefore trivially meets the criteria.
> 
> Signed-off-by: Pavel Begunkov <[email protected]>
> ---
>  drivers/char/mem.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/char/mem.c b/drivers/char/mem.c
> index 1c596b5cdb27..531f144d7132 100644
> --- a/drivers/char/mem.c
> +++ b/drivers/char/mem.c
> @@ -495,6 +495,8 @@ static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter)
>  		written += n;
>  		if (signal_pending(current))
>  			return written ? written : -ERESTARTSYS;
> +		if (iocb->ki_flags & IOCB_NOWAIT)
> +			return written ? written : -EAGAIN;
>  		cond_resched();
>  	}

I don't think this part is needed.

>  	return written;
> @@ -696,11 +698,11 @@ static const struct memdev {
>  #ifdef CONFIG_DEVMEM
>  	 [DEVMEM_MINOR] = { "mem", 0, &mem_fops, FMODE_UNSIGNED_OFFSET },
>  #endif
> -	 [3] = { "null", 0666, &null_fops, 0 },
> +	 [3] = { "null", 0666, &null_fops, FMODE_NOWAIT },
>  #ifdef CONFIG_DEVPORT
>  	 [4] = { "port", 0, &port_fops, 0 },
>  #endif
> -	 [5] = { "zero", 0666, &zero_fops, 0 },
> +	 [5] = { "zero", 0666, &zero_fops, FMODE_NOWAIT },
>  	 [7] = { "full", 0666, &full_fops, 0 },
>  	 [8] = { "random", 0666, &random_fops, 0 },
>  	 [9] = { "urandom", 0666, &urandom_fops, 0 },
> 

This looks fine.

-- 
Jens Axboe


  parent reply	other threads:[~2021-09-08 12:57 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-08 10:06 [PATCH] /dev/mem: nowait zero/null ops Pavel Begunkov
2021-09-08 10:25 ` Greg Kroah-Hartman
2021-09-08 10:54   ` Pavel Begunkov
2021-09-08 12:57 ` Jens Axboe [this message]
2021-09-08 13:07   ` Pavel Begunkov
2021-09-08 13:53     ` Jens Axboe

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox