Re: [PATCH 09/10] libfrog: improve ramdisk handling in platform_flush_device

[Christoph Hellwig <hch@lst.de>]

On Fri, Sep 25, 2026 at 03:47:20PM -0700, Darrick J. Wong wrote:
> > +	 * Historically the ram disk driver destroyed all data when BLKFLSBUF
> > +	 * was called.  That has been fixed a long time, but still be careful.
> > +	 */
> > +	if (S_ISBLK(st.st_mode) && major(st.st_rdev) != RAMDISK_MAJOR)
> >  		return ioctl(fd, BLKFLSBUF, 0);
> 
> BLKFLSBUF support on ramdisks hasn't been in the kernel since commit
> ff26956875c2f0 ("brd: remove support for BLKFLSBUF") which was merged in
> 4.10 in late 2016.  Maybe we should remove it?

People use xfsprogs on really old kernels.  Now no one really should
care about data integrity on a ramdisk, but there's not too much downside
of just keeping it, so I'd rather leave it alone.

The real question to be is why we even bother with BLKFLSBUF at all.
It seems to come from e2fsprogs, where that is optionally called from
ext2fs_sync_device with a a comment:

	... and optionally attempt to
	flush the buffer cache.  The latter is basically only useful for
	system benchmarks and for torturing systems in burn-in tests.  :)

but despite that comment, all caller do set that flag.

btrfsprogs and f2fs-tool do not have any calls to BLKFLSBUF.