AW: Re: open(2) with side effects

[Fiedler Roman <Roman.Fiedler () ait ac at>]

> Von: Florian Weimer [mailto:fweimer () redhat com]
>
> On 04/23/2015 04:16 PM, Stephane Chazelas wrote:
> > 2015-04-23 15:08:43 +0200, Florian Weimer:
> > > How common are file names on Linux which, when just opened and closed
> > > (maybe with fstat or fgetattr inbetween), trigger side effects, such as
> > > tape rewind?
> > [...]
> >
> > Depends what you mean by side effect.
>
> I'm only interested in side effects which are visible to other users and
> not directly related to global resource consumption (e.g., dentry usage
> or disk space due to keeping open a deleted file).
>
> Pretend that I'm writing a backup tool or something AV-like, which has
> to files without interfering with anything else.

Well, then make sure that you only use the openat calls and walk only a
single level of directory at any time. Otherwise O_NOFOLLOW is futile and
any file or /proc/[pid]/ data may end up in the backup or to be AV-scanned.

I would avoid going over FUSE-mounts also, there are so many ways to block
the process or play tricks with changing directory content.

And of course, have fd 0/1/2 open before opening anything else writable,
otherwise random open and error message may have unexpected side effects

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