Re: Any way to allow clobbering empty files when noclobber is set?

[Daniel Shahaf <d.s@xxxxxxxxxxxxxxxxxx>]

Bart Schaefer wrote on Sat, 06 Jun 2020 00:08 -0700:
> On Fri, Jun 5, 2020 at 9:55 PM Daniel Shahaf <d.s@xxxxxxxxxxxxxxxxxx> wrote:
> >
> > Bart Schaefer wrote on Fri, 05 Jun 2020 18:41 -0700:  
> > >
> > > I don't think that's the intended typical usage of noclobber.  It's
> > > not set by default, and it can't have any effect outside the local
> > > shell.  
> >
> > NO_CLOBBER causes open() to be called with the O_EXCL bit, which does
> > affect other processes as well.  
> 
> ??  All that O_EXCL guarantees is that no other process is able to
> create the file.  Once it exists, another file can open it and
> truncate it and write to it, unless prevented by umask.

But in Roman's example, _both_ backgrouned processes use O_EXCL, so
whichever process loses the race will get an error when it calls
open(2).  Yes, attempts to open() the file without O_EXCL will succeed,
but when a file is used as a mutex, everyone who tries to open the file
will try to use O_EXCL.

Makes sense?

Cheers,

Daniel