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

Uladzislau Rezki
2025-11-19T08:43:18Z

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