From: Al Viro <viro@ZenIV.linux.org.uk>
To: Miklos Szeredi <mszeredi@redhat.com>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
David Howells <dhowells@redhat.com>,
Tyler Hicks <tyhicks@canonical.com>
Subject: Re: [PATCH 00/17] clean up readlinks
Date: Tue, 27 Sep 2016 04:10:19 +0100 [thread overview]
Message-ID: <20160927031019.GF19539@ZenIV.linux.org.uk> (raw)
In-Reply-To: <1473708559-12714-1-git-send-email-mszeredi@redhat.com>
On Mon, Sep 12, 2016 at 09:29:02PM +0200, Miklos Szeredi wrote:
> The first patch is actually a bug fix, but I put it into this bunch for
> simplicity...
>
> The rest are really cleanups as well as minor bugfixes that are byproducts
> of the cleanups.
>
> This series builds on the fact that i_op.readlink is already set to
> generic_readlink() in 43/50 of the cases. And of those 7 only 4 are doing
> something special. So more than 90% of readlinks are/could actually just
> call back into get_link.
>
> The interesting cases are:
>
> - AFS, which has readlink but not get_link
> - proc, that allow jumping while following symlinks
>
> The first is handled by setting IOP_NOFOLLOW on the inode by the fs.
>
> The second one is handled by introducing is_following_link() which returns
> a bool depending on whether current->nameidata is NULL or not. If it
> returns false ->get_link() should behave as ->readlink() did. Otherwise it
> should behave as id did previously.
>
> Builds and boots. Can even read symlinks.
I have no problem with "let's get rid of generic_readlink" - not that
it bought us much, but sure, if you want to have decision made based upon
the combination of flags, let's do it. Just make NULL ->readlink + non-NULL
->get_link() mean generic_readlink(), and we are done. Especially if you
do the usual "set the flag on inode the first time we need to check".
I also have no problem with overlayfs and ecryptfs assuming that we only deal
with normal symlinks.
Overloading ->get_link() for procfs-style ones is just plain wrong,
though. Your current->nameidata != NULL thing is bloody brittle - what
happens if some code triggers those readlinks when called by something
during pathname resolution? Sure, right now existing callers won't.
But it doesn't take much to grow such a place _and_ have the implications
go unnoticed for quite a while.
next prev parent reply other threads:[~2016-09-27 3:10 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-12 19:29 [PATCH 00/17] clean up readlinks Miklos Szeredi
2016-09-12 19:29 ` [PATCH 01/17] bad_inode: add missing i_op initializers Miklos Szeredi
2016-09-12 19:29 ` [PATCH 02/17] ovl: use generic_readlink Miklos Szeredi
2016-09-12 19:29 ` [PATCH 03/17] proc/self: " Miklos Szeredi
2016-09-12 19:29 ` [PATCH 04/17] afs: " Miklos Szeredi
2016-09-12 19:29 ` [PATCH 05/17] bad_inode: " Miklos Szeredi
2016-09-12 19:29 ` [PATCH 06/17] vfs: remove page_readlink() Miklos Szeredi
2016-09-12 19:29 ` [PATCH 07/17] vfs: add is_following_link() helper Miklos Szeredi
2016-09-12 19:29 ` [PATCH 08/17] proc: merge proc_pid_readlink() into proc_pid_get_link() Miklos Szeredi
2016-09-12 19:29 ` [PATCH 09/17] proc: merge proc_ns_readlink() into proc_ns_get_link() Miklos Szeredi
2016-09-12 19:29 ` [PATCH 10/17] nsfs: clean up ns_get_name() interface Miklos Szeredi
2016-09-12 19:29 ` [PATCH 11/17] vfs: replace calling i_op->readlink with vfs_readlink() Miklos Szeredi
2016-09-12 19:29 ` [PATCH 12/17] vfs: remove ".readlink = generic_readlink" assignments Miklos Szeredi
2016-09-12 19:29 ` [PATCH 13/17] vfs: remove unused i_op->readlink Miklos Szeredi
2016-09-12 19:29 ` [PATCH 14/17] vfs: remove unused generic_readlink() Miklos Szeredi
2016-09-12 19:29 ` [PATCH 15/17] vfs: add vfs_get_link() helper Miklos Szeredi
2016-09-12 19:29 ` [PATCH 16/17] ovl: use vfs_get_link() Miklos Szeredi
2016-09-12 19:29 ` [PATCH 17/17] ecryptfs: " Miklos Szeredi
2016-09-27 3:10 ` Al Viro [this message]
2016-09-27 9:38 ` [PATCH 00/17] clean up readlinks Miklos Szeredi
2016-09-28 2:17 ` Al Viro
2016-09-28 14:47 ` Miklos Szeredi
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