Re: [Question] why not flush device cache at _vg_commit_raw

On Wed, Jan 24, 2024 at 01:35:49PM +0100, Zdenek Kabelac wrote:
> I guess our dev_flush() function is mostly handling all those cases properly
> with the use of  ioctl(BLKFLSBUF).

This ioctl by itself will only flush the page cache and not device
caches, but it is indeed followed by a fsync on the blockdev which is
basically the only way for userspace to trigger a device cache flush
when operating directly on a block device.

> The only problem is - it's usage somehow vanished - and even in the past
> it's been  basically used only for non-direct usage so likely still not
> correct.

Indeed, the device cache flushing is required for data integrity
irrespective of the io mode (unless O_DSYNC/RWF_DSYNC), direct-io only
obviates the need for flushing the page cache.

Regards,
Anthony