linux-kernel - Re: [RFC][PATCH v2] procfs: Always expose /proc/<pid>/map

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Date:	Wed, 28 Jan 2015 00:46:05 +0300
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Kees Cook <keescook@...omium.org>,
	Cyrill Gorcunov <gorcunov@...il.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Calvin Owens <calvinowens@...com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Peter Feiner <pfeiner@...gle.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Siddhesh Poyarekar <siddhesh.poyarekar@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, <kernel-team@...com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: [RFC][PATCH v2] procfs: Always expose /proc/<pid>/map_files/
 and make it readable


>>> Are mount namespaces handled in this output?
>>
>> Could you clarify this moment, i'm not sure i get it.
> 
> I changed how I asked this question in my review of the documentation,
> but it looks like these symlinks aren't "regular" symlinks (that are
> up to the follower to have access to the file system path shown), but
> rather they bypass VFS. As a result, I'm wondering how things like
> mount namespaces might change this behavior: what is shown, the path
> from the perspective of the target, or from the viewer (which may be
> in separate mount namespaces).

These work just like the /proc/$pid/fd/$n links do. When you readlink
on it the d_path() is called which walks up the dentry/vfsmnt tree
until it reaches either current root or the global one. For "another"
mount namespace case it produces the path relative to this namespace's
root.

Thanks,
Pavel

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