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Re: Any way to allow clobbering empty files when noclobber is set?
- X-seq: zsh-workers 46002
- From: Daniel Shahaf <d.s@xxxxxxxxxxxxxxxxxx>
- To: Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>
- Subject: Re: Any way to allow clobbering empty files when noclobber is set?
- Date: Sat, 6 Jun 2020 08:03:03 +0000
- Cc: "zsh-workers@xxxxxxx" <zsh-workers@xxxxxxx>, Martin Tournoij <martin@xxxxxxxxxx>
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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.
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