From: Jann Horn <jannh@google.com>
To: Aleksa Sarai <cyphar@cyphar.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
Michael Kerrisk <mtk.manpages@gmail.com>,
Christian Brauner <christian@brauner.io>,
Aleksa Sarai <asarai@suse.de>,
linux-man <linux-man@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
kernel list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RFC 1/3] symlink.7: document magic-links more completely
Date: Mon, 7 Oct 2019 18:36:40 +0200 [thread overview]
Message-ID: <CAG48ez2LuOGAXgKftZKfDKxhdb6xcBTdoK468-HXdcpxCW4r4w@mail.gmail.com> (raw)
In-Reply-To: <20191003145542.17490-2-cyphar@cyphar.com>
On Thu, Oct 3, 2019 at 4:56 PM Aleksa Sarai <cyphar@cyphar.com> wrote:
> Traditionally, magic-links have not been a well-understood topic in
> Linux. Given the new changes in their semantics (related to the link
> mode of trailing magic-links), it seems like a good opportunity to shine
> more light on magic-links and their semantics.
[...]
> +++ b/man7/symlink.7
> @@ -84,6 +84,25 @@ as they are implemented on Linux and other systems,
> are outlined here.
> It is important that site-local applications also conform to these rules,
> so that the user interface can be as consistent as possible.
> +.SS Magic-links
> +There is a special class of symlink-like objects known as "magic-links" which
I think names like that normally aren't hypenated in english, and
instead of "magic-links", it'd be "magic links"? Just like how you
wouldn't write "symbolic-link", but "symbolic link". But this is
bikeshedding, and if you disagree, feel free to ignore this comment.
> +can be found in certain pseudo-filesystems such as
> +.BR proc (5)
> +(examples include
> +.IR /proc/[pid]/exe " and " /proc/[pid]/fd/* .)
> +Unlike normal symlinks, magic-links are not resolved through
nit: AFAICS symlinks are always referred to as "symbolic links"
throughout the manpages.
> +pathname-expansion, but instead act as direct references to the kernel's own
> +representation of a file handle. As such, these magic-links allow users to
> +access files which cannot be referenced with normal paths (such as unlinked
> +files still referenced by a running program.)
Could maybe add "and files in different mount namespaces" as another
example here; at least for me, that's the main usecases for
/proc/*/root.
[...]
> +However, magic-links do not follow this rule. They can have a non-0777 mode,
> +which is used for permission checks when the final
> +component of an
> +.BR open (2)'s
Maybe leave out the "open" part, since the same restriction has to
also apply to other syscalls operating on files, like truncate() and
so on?
> +path is a magic-link (see
> +.BR path_resolution (7).)
next prev parent reply other threads:[~2019-10-07 16:37 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-03 14:55 [PATCH RFC 0/3] document openat2(2) patch series Aleksa Sarai
2019-10-03 14:55 ` [PATCH RFC 1/3] symlink.7: document magic-links more completely Aleksa Sarai
2019-10-07 16:36 ` Jann Horn [this message]
2019-10-08 1:33 ` Aleksa Sarai
2019-10-09 7:55 ` Michael Kerrisk (man-pages)
2019-10-09 9:57 ` Aleksa Sarai
2020-04-17 11:39 ` Michael Kerrisk (man-pages)
2020-04-17 15:37 ` Aleksa Sarai
2020-05-15 11:42 ` Michael Kerrisk (man-pages)
2019-10-03 14:55 ` [PATCH RFC 2/3] open.2: add O_EMPTYPATH documentation Aleksa Sarai
2019-10-09 8:01 ` Michael Kerrisk (man-pages)
2019-10-09 10:00 ` Aleksa Sarai
2019-10-03 14:55 ` [PATCH RFC 3/3] openat2.2: document new openat2(2) syscall Aleksa Sarai
2019-10-09 8:36 ` Michael Kerrisk (man-pages)
2019-10-09 10:17 ` Aleksa Sarai
2019-10-09 10:32 ` Michael Kerrisk (man-pages)
2019-10-03 14:55 ` [PATCH RFC 3/3] openat2.2: document new syscall Aleksa Sarai
2019-10-03 15:00 ` Aleksa Sarai
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