From: Daniel Shahaf <d.s@daniel.shahaf.name>
To: Bart Schaefer <schaefer@brasslantern.com>
Cc: "zsh-workers@zsh.org" <zsh-workers@zsh.org>,
Martin Tournoij <martin@arp242.net>
Subject: Re: Any way to allow clobbering empty files when noclobber is set?
Date: Fri, 5 Jun 2020 01:59:48 +0000 [thread overview]
Message-ID: <20200605015948.0c26ca38@tarpaulin.shahaf.local2> (raw)
In-Reply-To: <CAH+w=7Yk6gbTKjzQ-N91X_hR_24wnBbxE+7TqrtoTc6cyocqmQ@mail.gmail.com>
Bart Schaefer wrote on Thu, 04 Jun 2020 13:35 -0700:
> On Thu, Jun 4, 2020 at 5:16 AM Peter Stephenson
> <p.w.stephenson@ntlworld.com> wrote:
> >
> > One thing I missed is that we already open the file and run fstat to
> > check if it's regular. We can simply check if it's empty at the
> > same point
>
> Exactly where my earlier question came from.
>
> > + if (isset(CLOBBEREMPTY) && buf.st_size == 0)
> > + {
> > + close(fd);
> > + return open(ufname, O_WRONLY | O_CREAT | O_TRUNC | O_NOCTTY,
> > + 0666);
> > + }
>
> Considering the concurrent-openers situation that Roman mentioned, I'm
> debating whether there is any benefit to doing:
>
> int newfd = open(ufname, O_WRONLY | O_CREAT | O_TRUNC | O_NOCTTY, 0666);
> close(fd);
> return newfd;
>
> I have a vague sense that keeping the descriptor open until the new
> file is created might prevent some races, but I can't recite an
> example.
This wouldn't prevent races, because the filename might be unlinked
between the first and second open(2) calls.
I think the right fix here is to simply change the body of the quoted
if statement to «return fd». What do we gain by re-opening the file
with the O_TRUNC flag set when we already know the file is
zero-length? It seems to me we're just introducing a race condition
for no reason.
prev parent reply other threads:[~2020-06-05 2:00 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20200603020919eucas1p13e26ebcbb335784d14bfb97b137f385a@eucas1p1.samsung.com>
2020-06-03 2:08 ` Martin Tournoij
2020-06-03 12:04 ` Peter Stephenson
2020-06-04 1:48 ` Daniel Shahaf
2020-06-04 2:43 ` Bart Schaefer
2020-06-04 4:06 ` Daniel Shahaf
2020-06-04 5:00 ` Bart Schaefer
2020-06-05 3:10 ` Daniel Shahaf
2020-06-05 3:18 ` Daniel Shahaf
2020-06-06 1:07 ` Bart Schaefer
2020-06-06 4:48 ` Daniel Shahaf
2020-06-06 7:04 ` Bart Schaefer
2020-06-04 6:31 ` Martin Tournoij
2020-06-05 2:22 ` Daniel Shahaf
2020-06-04 2:13 ` Vin Shelton
2020-06-04 2:35 ` Bart Schaefer
2020-06-04 2:36 ` Daniel Shahaf
2020-06-04 11:57 ` Vin Shelton
2020-06-04 5:06 ` Bart Schaefer
2020-06-04 5:41 ` Roman Perepelitsa
2020-06-05 2:07 ` Daniel Shahaf
2020-06-05 4:38 ` Roman Perepelitsa
2020-06-06 1:41 ` Bart Schaefer
2020-06-06 4:55 ` Daniel Shahaf
2020-06-06 6:25 ` Roman Perepelitsa
2020-06-06 7:08 ` Bart Schaefer
2020-06-06 8:03 ` Daniel Shahaf
[not found] ` <1941572212.466119.1591360860372@mail2.virginmedia.com>
[not found] ` <e7f7dfe2-eb4a-457b-85fb-091935a74c0e@www.fastmail.com>
2020-06-06 11:57 ` Peter Stephenson
2020-06-06 12:48 ` Roman Perepelitsa
2020-06-06 15:24 ` Bart Schaefer
2020-06-06 16:24 ` Peter Stephenson
2020-06-07 11:55 ` Daniel Shahaf
2020-06-07 17:00 ` Peter Stephenson
2020-06-08 3:27 ` Daniel Shahaf
2020-06-08 9:30 ` Peter Stephenson
2020-06-07 17:20 ` Bart Schaefer
2020-06-06 15:09 ` Bart Schaefer
2020-06-04 6:47 ` Martin Tournoij
2020-06-04 9:42 ` Peter Stephenson
2020-06-04 12:20 ` Roman Perepelitsa
2020-06-04 12:26 ` Peter Stephenson
2020-06-04 12:15 ` Peter Stephenson
2020-06-04 20:35 ` Bart Schaefer
2020-06-05 1:59 ` Daniel Shahaf [this message]
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