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Date: Wed, 22 Oct 2025 10:02:51 +0200
From: Christoph Hellwig <hch@lst.de>
To: Kanchan Joshi <joshi.k@samsung.com>
Cc: Christoph Hellwig <hch@lst.de>, kbusch@kernel.org, axboe@kernel.dk,
	brauner@kernel.org, josef@toxicpanda.com, jack@suse.cz,
	jlayton@kernel.org, linux-fsdevel@vger.kernel.org,
	linux-block@vger.kernel.org, gost.dev@samsung.com
Subject: Re: [RFC PATCH 4/5] fs: propagate write stream
Message-ID: <20251022080251.GB9997@lst.de>
References: <20250729145135.12463-1-joshi.k@samsung.com> <CGME20250729145338epcas5p4da42906a341577997f39aa8453252ea3@epcas5p4.samsung.com> <20250729145135.12463-5-joshi.k@samsung.com> <20250812082404.GD22212@lst.de> <78e760ed-1ba3-4a06-ac51-45b4cd2c05e0@samsung.com>
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On Thu, Oct 16, 2025 at 03:17:50PM +0530, Kanchan Joshi wrote:
> On 8/12/2025 1:54 PM, Christoph Hellwig wrote:
> > On Tue, Jul 29, 2025 at 08:21:34PM +0530, Kanchan Joshi wrote:
> >> bio->bi_write_stream is not set by the filesystem code.
> >> Use inode's write stream value to do that.
> > Just passing it through is going to create problems.  i.e. when
> > the file system does it's own placement or reserves ids.  We'll need
> > an explicit intercept point between the user write stream and what
> > does into the bio.
> > 
> 
> For that intercept point - will you prefer a generic helper, say 
> fs_resolve_write_stream(), that will call a new inode operation that 
> filesystem will implement?

I don't remember what the patch was doing, but basically the file system
should be explicitly set bio->bi_write_stream instead of automatically
inheriting it.  Where the file system uses helpers we'll have to find
a way to propagate it.  For iomap one option could be to make the file
system return it in struct iomap.