Re: Direct I/O

On Wed, Apr 12, 2023 at 5:48 PM Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:
> On Wed, Apr 12, 2023 at 3:04 PM Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:
> > On Wed, Apr 12, 2023 at 2:56 PM Christoph Berg <myon(at)debian(dot)org> wrote:
> > > I'm hitting a panic in t_004_io_direct. The build is running on
> > > overlayfs on tmpfs/ext4 (upper/lower) which is probably a weird
> > > combination but has worked well for building everything over the last
> > > decade. On Debian unstable:

After trying a couple of things and doing some googling, it looks like
it's tmpfs that rejects it, not overlayfs, so I'd adjust that commit
message slightly. Of course it's a completely reasonable thing to
expect the tests to pass (or in this case be skipped) in a tmpfs, eg
/tmp on some distributions. (It's a strange to contemplate what
O_DIRECT means for tmpfs, considering that it *is* the page cache,
kinda, and I see people have been arguing about that for a couple of
decades since O_DIRECT was added to Linux; doesn't seem that helpful
to me that it rejects it, but 🤷).