linux-kernel - Re: [PATCH 3/6] fs: clear FMODE

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Date:   Fri, 24 Jun 2022 18:04:19 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 3/6] fs: clear FMODE_LSEEK if no llseek function

On Fri, Jun 24, 2022 at 06:56:28PM +0200, Jason A. Donenfeld wrote:
> This helps unify a longstanding wart where FMODE_LSEEK hasn't been
> uniformly unset when it should be.
> 
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
>  fs/file_table.c | 2 ++
>  fs/open.c       | 2 ++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/fs/file_table.c b/fs/file_table.c
> index 5424e3a8df5f..15700b2e1b53 100644
> --- a/fs/file_table.c
> +++ b/fs/file_table.c
> @@ -241,6 +241,8 @@ static struct file *alloc_file(const struct path *path, int flags,
>  	if ((file->f_mode & FMODE_WRITE) &&
>  	     likely(fop->write || fop->write_iter))
>  		file->f_mode |= FMODE_CAN_WRITE;
> +	if ((file->f_mode & FMODE_LSEEK) && !file->f_op->llseek)
> +		file->f_mode &= ~FMODE_LSEEK;

	Where would FMODE_LSEEK come from in this one?  ->f_mode is set
(in __alloc_file()) to OPEN_FMODE(flags); that does deal with FMODE_READ
and FMODE_WRITE, but FMODE_LSEEK will be clear...