Re: [RFC PATCH 1/2] fs: introduce FALLOC_FL_FORCE_ZERO to fallocate

[Christoph Hellwig]

On Mon, Jan 06, 2025 at 11:17:32AM -0500, Theodore Ts'o wrote:
> Yes.  And we might decide that it should be done using some kind of
> ioctl, such as BLKDISCARD, as opposed to a new fallocate operation,
> since it really isn't a filesystem metadata operation, just as
> BLKDISARD isn't.  The other side of the argument is that ioctls are
> ugly, and maybe all new such operations should be plumbed through via
> fallocate as opposed to adding a new ioctl.  I don't have strong
> feelings on this, although I *do* belive that whatever interface we
> use, whether it be fallocate or ioctl, it should be supported by block
> devices and files in a file system, to make life easier for those
> databases that want to support running on a raw block device (for
> full-page advertisements on the back cover of the Businessweek
> magazine) or on files (which is how 99.9% of all real-world users
> actually run enterprise databases.  :-)

If you want the operation to work for files it needs to be routed
through the file system as otherwise you can't make it actually
work coherently.  While you could add a new ioctl that works on a
file fallocate seems like a much better interface.  Supporting it
on a block device is trivial, as it can mostly (or even entirely
depending on the exact definition of the interface) reuse the existing
zero range / punch hole code.