linux-kernel - Re: [RESEND PATCH] dm-ebs: Mark full buffer dirty even on partial write

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Message-ID: <aR2DIXsymZWD9EvG@pc636>
Date: Wed, 19 Nov 2025 09:43:13 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: Christoph Hellwig <hch@....de>
Cc: Mikulas Patocka <mpatocka@...hat.com>,
	Benjamin Marzinski <bmarzins@...hat.com>,
	Uladzislau Rezki <urezki@...il.com>,
	Alasdair Kergon <agk@...hat.com>, DMML <dm-devel@...ts.linux.dev>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Snitzer <snitzer@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH] dm-ebs: Mark full buffer dirty even on partial
 write

On Wed, Nov 19, 2025 at 06:46:35AM +0100, Christoph Hellwig wrote:
> On Tue, Nov 18, 2025 at 06:21:56PM +0100, Mikulas Patocka wrote:
> > OK - I accepted Uladzislau's patch. As logical block size and physical 
> > block size seem to be unreliable, it's better to set the size in dm-ebs.
> 
> logical and physical block size are reliable.  Uladzislau just seems
> to have a completely broken device that needs fixing, because it will
> run into all kinds of other problems otherwise.
> 
Well. LBA is fixed in my case. Just only one format which is 512B.

Whereas the I/O can not be performed by using LBAs sizes. It is fixed
and bigger.

I rely on this:

<snip>
/*
 * Construct an emulated block size mapping: <dev_path> <offset> <ebs> [<ubs>]
 *
 * <dev_path>: path of the underlying device
 * <offset>: offset in 512 bytes sectors into <dev_path>
 * <ebs>: emulated block size in units of 512 bytes exposed to the upper layer
 * [<ubs>]: underlying block size in units of 512 bytes imposed on the lower layer;
 *	    optional, if not supplied, retrieve logical block size from underlying device
 */
static int ebs_ctr(struct dm_target *ti, unsigned int argc, char **argv)
{
...
<snip>

to do RMW. It says if UBS is set, data has to impose to lower layer
in sizes of UBS and aligned to UBS. I specify the UBS what my device
is capable of reading/writing.

The buffer is correctly updated in terms of RMW in UBS window. But it
flushes partly leading to I/O errors. I find it wrong. Because i set
the desired underlying block size.

That is my concern.

--
Uladzislau Rezki