From: Bart Schaefer <schaefer@brasslantern.com>
To: Daniel Shahaf <d.s@daniel.shahaf.name>
Cc: Peter Stephenson <p.w.stephenson@ntlworld.com>,
"zsh-workers@zsh.org" <zsh-workers@zsh.org>
Subject: Re: Any way to allow clobbering empty files when noclobber is set?
Date: Sun, 7 Jun 2020 10:20:37 -0700 [thread overview]
Message-ID: <CAH+w=7YzW4jSsWv4bBDUFYPUTSBP0e4MtfF3c77YsB4VKz5BsA@mail.gmail.com> (raw)
In-Reply-To: <20200607115515.6624e240@tarpaulin.shahaf.local2>
On Sun, Jun 7, 2020 at 4:55 AM Daniel Shahaf <d.s@daniel.shahaf.name> wrote:
>
> In the clobbering open, we use O_CREAT|O_TRUNC, which means: if it
> doesn't exist, create it; if it already exists, truncate it. If some
> other process calls open() on the same file immediately after our
> open() [or subsequent write()] call returns, there's nothing we can do
> about that.
Also if another process already had the existing file open, whatever
it was doing will be lost. (Aside: If it's an NFS file, and the
other process continues writing, this often results in a block of NUL
bytes where the NFS server fills in between the two write positions.)
> As to CLOBBER_EMPTY, the situation is similar. We can call open() with
> O_CREAT but neither O_EXCL nor O_TRUNC and then fstat() the resulting
> file. The same race conditions as in the previous paragraphs exist
> here too — for example, someone could open() and write() to the file
> after we fstat() it — but we neither can nor need to do any better
> about races in this case than in the others.
This in fact avoids (or at least does a better job of avoiding) the
problem with two different write positions if some other process has
already opened the file for write.
next prev parent reply other threads:[~2020-06-07 17:21 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 [this message]
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
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