Re: [PATCH 02/29] block: Use bdev_open_by_dev() in blkdev_open()

From: Al Viro <viro@zeniv.linux.org.uk>
To: Jan Kara <jack@suse.cz>
Cc: linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org,
	Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 02/29] block: Use bdev_open_by_dev() in blkdev_open()
Date: Fri, 25 Aug 2023 02:14:09 +0100	[thread overview]
Message-ID: <20230825011409.GA95084@ZenIV> (raw)
In-Reply-To: <20230811110504.27514-2-jack@suse.cz>

On Fri, Aug 11, 2023 at 01:04:33PM +0200, Jan Kara wrote:

> @@ -478,7 +478,7 @@ blk_mode_t file_to_blk_mode(struct file *file)
>  		mode |= BLK_OPEN_READ;
>  	if (file->f_mode & FMODE_WRITE)
>  		mode |= BLK_OPEN_WRITE;
> -	if (file->private_data)
> +	if (file->f_flags & O_EXCL)
>  		mode |= BLK_OPEN_EXCL;
>  	if (file->f_flags & O_NDELAY)
>  		mode |= BLK_OPEN_NDELAY;

> index 3be11941fb2d..47f216d8697f 100644
> --- a/block/ioctl.c
> +++ b/block/ioctl.c
> @@ -575,7 +575,7 @@ long blkdev_ioctl(struct file *file, unsigned cmd, unsigned long arg)
>  {
>  	struct block_device *bdev = I_BDEV(file->f_mapping->host);
>  	void __user *argp = (void __user *)arg;
> -	blk_mode_t mode = file_to_blk_mode(file);
> +	blk_mode_t mode = ((struct bdev_handle *)file->private_data)->mode;

Take a look at sd_ioctl() and note that fcntl(2) can be used to set/clear O_NDELAY.
The current variant works since we recalculate mode every time; this one will end up
stuck with whatever we had at open time.  Note that Christoph's series could do this
in blkdev_ioctl()
-       /*
-        * O_NDELAY can be altered using fcntl(.., F_SETFL, ..), so we have
-        * to updated it before every ioctl.
-        */
-       if (file->f_flags & O_NDELAY)
-               mode |= FMODE_NDELAY;
-       else
-               mode &= ~FMODE_NDELAY;
precisely because his file_to_blk_mode() picks O_NDELAY from flags when blkdev_ioctl()
calls it.

The same goes for compat counterpart of that thing.  Both need to deal with that
scenario - you need something that would pick the O_NDELAY updates from ->f_flags.

Al, trying to catch up on the awful pile of mail that has accumulated over the 3 months
of being net.dead...