linux-kernel - Re: [PATCH 07/12] fs: add RWF_UNCACHED iocb and FOP_UNCACHED file

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Message-ID: <Z1gkg68w-G9151cC@infradead.org>
Date: Tue, 10 Dec 2024 03:22:43 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Jens Axboe <axboe@...nel.dk>
Cc: linux-mm@...ck.org, linux-fsdevel@...r.kernel.org, hannes@...xchg.org,
	clm@...a.com, linux-kernel@...r.kernel.org, willy@...radead.org,
	kirill@...temov.name, bfoster@...hat.com
Subject: Re: [PATCH 07/12] fs: add RWF_UNCACHED iocb and FOP_UNCACHED
 file_operations flag

On Tue, Dec 03, 2024 at 08:31:43AM -0700, Jens Axboe wrote:
> +	if (flags & RWF_UNCACHED) {
> +		/* file system must support it */
> +		if (!(ki->ki_filp->f_op->fop_flags & FOP_UNCACHED))
> +			return -EOPNOTSUPP;
> +		/* DAX mappings not supported */
> +		if (IS_DAX(ki->ki_filp->f_mapping->host))
> +			return -EOPNOTSUPP;

I'd argue that DAX is always uncached and could just ignore the flag.
Same for direct I/O.