[PATCH v2 4/6] cmd: Add flush support for all blk devices

[dmukhin at ford.com]

Hi Sean,

Thanks for the feedback!

On Wed, Jun 03, 2026 at 01:43:10PM -0400, Sean Anderson wrote:
> On 5/28/26 23:44, dmukhin at ford.com wrote:
> > From: Denis Mukhin <dmukhin at ford.com>
> > 
> > Introduce `flush` subcommand for all blk devices to allow committing
> > dirty data explicitly to the given block device.
> 
> Shouldn't this be done automatically as part of blk_write? Similar to
> how all FS operations in U-Boot look like
> 
> - Mount FS
> - Perform operation
> - Unmount FS
> 
> so the FS is never in an inconsistent state once an operation completes.
> 
> Is the performance impact too much? I'm just concerned that a lot of
> existing code assumes that blk_write is persistent and that it's OK
> to e.g. immediately reset after blk_write returns.

In my case I need to update the GPT-backed boot counter; there are two
GPT headers, primary and backup, so I used blk_dflush() to guarantee that
both headers are updated before jumping into the OS.

So in my scenario I need to ensure that those 2 writes will land to the
NVMe.

I think FUA suggested by Neil in v1 feedback should be a robust solution
for NVMe, but I went with a 'flush' solution first.

> 
> --Sean