From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Wed, 10 Apr 2019 02:39:34 +0100 From: Al Viro Subject: Re: [PATCH] fscrypt: cache decrypted symlink target in ->i_link Message-ID: <20190410013934.GV2217@ZenIV.linux.org.uk> References: <20190409233544.156665-1-ebiggers@kernel.org> <20190410003346.GT2217@ZenIV.linux.org.uk> <20190410004553.GA2454@sol.localdomain> <20190410010425.GU2217@ZenIV.linux.org.uk> <20190410012247.GB2454@sol.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190410012247.GB2454@sol.localdomain> Sender: Al Viro To: Eric Biggers Cc: linux-fscrypt@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net List-ID: On Tue, Apr 09, 2019 at 06:22:49PM -0700, Eric Biggers wrote: > > Non-NULL ->get_link() => DCACHE_SYMLINK_TYPE in ->d_flags => > > d_is_symlink() true => step_into() progresses to pick_link(). > > > > IOW, non-NULL ->get_link() is what tells you that we have > > a symlink there. > > I think that's pretty unintuitive. The fact that multiple filesystems including > ext4 set ->i_link on fast symlinks, then set ->get_link() to a function that > returns ->i_link, made me assume that's the mechanism by which such symlink > targets are returned to the VFS. When in fact fs/namei.c just uses ->i_link, > and never calls ->get_link(). > > Is there any reason why d_flags_for_inode() doesn't check S_ISLNK() instead, and > then fs/namei.c would call ->get_link() if non-NULL, otherwise use ->i_link? Extra check and dereference on hot path with no visible benefits of doing it that way, for starters. Really, what _is_ the benefit of pessimizing that? Most of the symlinks we run into will have ->i_link set; checking ->i_op->get_link first is extra work for no good reason... What's more, ->get_link is visible in inode_operations; ->i_link (let alone ->i_mode) isn't. As it is, we can easily tell symlink inode_operations from everything else on the source level. With your scheme we won't.