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From: Nikolaus Rath <Nikolaus@rath.org>
To: linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>, Neil Brown <neil@brown.name>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Subject: Behaviour of /proc/self/fd/NN
Date: Wed, 14 Nov 2018 10:45:19 +0000
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Hi,

If I understand Documentation/filesystems/path-lookup.md correctly, then
the "symlinks" in /proc/self/fd/NN are not true symlinks but just
presented as such to userspace. Does this mean that I can access (e.g.,
open(), setxattr(), or chmod()) these files without the possibility of
race conditions? I.e., there is no way for someone to rename the target
after the kernel has "looked up" the target but before the operation is
applied?

Secondly, under which conditions can I open the files in /proc? Does
this still work if the destination file has been unlinked? Does it
always follow renames? What if I mounted something over the destination?

(Background: I'm trying to ascertain how well a true bind mount can be
emulated by a passthrough FUSE filesystem).

Best,
-Nikolaus
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