Re: [PATCH 0/4] uapi, vfs: Change the mount API UAPI [ver #2]

[Christian Brauner <christian@brauner.io>]

On Thu, May 16, 2019 at 05:22:59PM +0100, Al Viro wrote:
> On Thu, May 16, 2019 at 12:52:04PM +0100, David Howells wrote:
> > 
> > Hi Linus, Al,
> > 
> > Here are some patches that make changes to the mount API UAPI and two of
> > them really need applying, before -rc1 - if they're going to be applied at
> > all.
> 
> I'm fine with 2--4, but I'm not convinced that cloexec-by-default crusade
> makes any sense.  Could somebody give coherent arguments in favour of
> abandoning the existing conventions?

So as I said in the commit message. From a userspace perspective it's
more of an issue if one accidently leaks an fd to a task during exec.

Also, most of the time one does not want to inherit an fd during an
exec. It is a hazzle to always have to specify an extra flag.

As Al pointed out to me open() semantics are not going anywhere. Sure,
no argument there at all.
But the idea of making fds cloexec by default is only targeted at fds
that come from separate syscalls. fsopen(), open_tree_clone(), etc. they
all return fds independent of open() so it's really easy to have them
cloexec by default without regressing anyone and we also remove the need
for a bunch of separate flags for each syscall to turn them into
cloexec-fds. I mean, those for syscalls came with 4 separate flags to be
able to specify that the returned fd should be made cloexec. The other
way around, cloexec by default, fcntl() to remove the cloexec bit is way
saner imho.

Christian