linux-kernel - How SHOULD inotify and hardlinks play together?

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Message-Id: <1239832148.2562.42.camel@localhost.localdomain>
Date:	Wed, 15 Apr 2009 17:49:08 -0400
From:	Eric Paris <eparis@...hat.com>
To:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Cc:	akpm@...ux-foundation.org, john@...nmccutchan.com, rlove@...ve.org,
	viro@...iv.linux.org.uk
Subject: How SHOULD inotify and hardlinks play together?

touch /tmp/file1 /tmp/file2
ln /tmp/file2 /tmp/hardlinktofile2

[A] Set up one inotify watch on /tmp/file2
[B] Set up another inotify watch on /tmp/hardlinktofile2

(they are both watching the same inode/data)

mv /tmp/file1 /tmp/file2

Right now, today, both [A] and [B] are going to get DELETE_SELF and
IGNORED messages and are not going to get any more notifications.

That might be fine for [A] since the pathname it ask to watch doesn't
exist any more (although I argue the inode still does), but that isn't
right for [B] since /tmp/hardlinktofile2 is still there, still it's own
inode, and still able to receive events, be modified, be read, be
deleted, whatever.  But after that mv operation neither [A] nor [B] will
get any more events what-so-ever.

So the question is, should inotify continue to clear all watches on an
inode when something else is moved on top if it even if i_nlink isn't
going to 0?  If not, should inotify continue to send a DELETE_SELF like
it does today?  Should it instead send an ATTRIB like it does when you
add a hard link?

-Eric

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