linux-kernel - Re: [PATCH 1/2] fs, close_range: add flag CLOSE_RANGE

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Date:   Tue, 13 Oct 2020 23:04:21 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Christian Brauner <christian.brauner@...ntu.com>,
        Giuseppe Scrivano <gscrivan@...hat.com>
Cc:     linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
        linux-fsdevel@...r.kernel.org,
        containers@...ts.linux-foundation.org
Subject: Re: [PATCH 1/2] fs, close_range: add flag CLOSE_RANGE_CLOEXEC

On 13/10/2020 22.54, Christian Brauner wrote:
> On Tue, Oct 13, 2020 at 04:06:08PM +0200, Giuseppe Scrivano wrote:
> 
> Hey Guiseppe,
> 
> Thanks for the patch!
> 
>> When the flag CLOSE_RANGE_CLOEXEC is set, close_range doesn't
>> immediately close the files but it sets the close-on-exec bit.
> 
> Hm, please expand on the use-cases a little here so people know where
> and how this is useful. Keeping the rationale for a change in the commit
> log is really important.
> 

> I think I don't have quarrels with this patch in principle but I wonder
> if something like the following wouldn't be easier to follow:
> 
> diff --git a/fs/file.c b/fs/file.c
> index 21c0893f2f1d..872a4098c3be 100644
> --- a/fs/file.c
> +++ b/fs/file.c
> @@ -672,6 +672,32 @@ int __close_fd(struct files_struct *files, unsigned fd)
>  }
>  EXPORT_SYMBOL(__close_fd); /* for ksys_close() */
>  
> +static inline void __range_cloexec(struct files_struct *cur_fds,
> +				   unsigned int fd, unsigned max_fd)
> +{
> +	struct fdtable *fdt;
> +	spin_lock(&cur_fds->file_lock);
> +	fdt = files_fdtable(cur_fds);
> +	while (fd <= max_fd)
> +		__set_close_on_exec(fd++, fdt);

Doesn't that want to be

  bitmap_set(fdt->close_on_exec, fd, max_fd - fd + 1)

to do word-at-a-time? I assume this would mostly be called with (3, ~0U)
as arguments or something like that.

Rasmus