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From: Miklos Szeredi <miklos@szeredi.hu>
To: Chengguang Xu <cgxu519@mykernel.net>
Cc: overlayfs <linux-unionfs@vger.kernel.org>
Subject: Re: [RFC PATCH 1/2] ovl: skip checking lower file's write permisson on truncate
Date: Tue, 20 Jul 2021 18:01:11 +0200	[thread overview]
Message-ID: <CAJfpegvmMtXPg1qMznuimy27maqGxOtcddR-L0MUfAS6jwhE7Q@mail.gmail.com> (raw)
In-Reply-To: <CAJfpegvmBggw3bgumMwDF_V_dgn=gvC+a+8oCgYfZ+Qu55U=vw@mail.gmail.com>

On Tue, 20 Jul 2021 at 17:19, Miklos Szeredi <miklos@szeredi.hu> wrote:

> So on one instance a file on lower gets executed and on another
> instance sharing the lower layer the file is truncated.  The truncate
> is currently denied due to the negative i_writecount on the lower
> file.  Also behavior is inconsistent between open(path, O_TRUNC) and
> truncate(path) even though the two should be equivalent.
>
> Applied with the following description:
>
[...]

Also adding the following documentation in the "Non-standard behavior" section:

c) If a file residing on a lower layer is being executed, then opening that
file for write or truncating the file will not be denied with ETXTBSY.

Looked at the POSIX standard and it only documents ETXTBUSY for O_RDWR
and O_WRONLY and not for truncate(2) or O_TRUNC.  So strictly speaking
this patch doesn't even change the POSIX correctness.

Thanks,
Miklos

  parent reply	other threads:[~2021-07-20 16:12 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-24 14:03 Chengguang Xu
2021-04-24 14:03 ` [RFC PATCH 2/2] ovl: enhance write permission check for writable open Chengguang Xu
2021-07-21 13:14   ` Miklos Szeredi
2021-04-28 12:18 ` 回复:[RFC PATCH 1/2] ovl: skip checking lower file's write permisson on truncate Chengguang Xu
2021-07-20 14:35 ` [RFC " Miklos Szeredi
2021-07-20 15:19   ` Miklos Szeredi
2021-07-20 16:01     ` Chengguang Xu
2021-07-20 16:01     ` Miklos Szeredi [this message]
2021-07-20 16:04       ` Chengguang Xu

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