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Date: Sun, 19 Feb 2017 09:05:56 +0000 From: Al Viro <viro@...IV.linux.org.uk> To: Miklos Szeredi <mszeredi@...hat.com> Cc: linux-unionfs@...r.kernel.org, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org Subject: Re: [PATCH 4/9] vfs: intercept reads to overlay files On Fri, Feb 17, 2017 at 05:09:33PM +0100, Miklos Szeredi wrote: > ...in order to handle the corner case when the file is copyied up after > being opened read-only. > --- /dev/null > +++ b/fs/overlay_util.c > @@ -0,0 +1,39 @@ > +/* > + * Copyright (C) 2017 Red Hat, Inc. > + * > + * This program is free software; you can redistribute it and/or modify it > + * under the terms of the GNU General Public License version 2 as published by > + * the Free Software Foundation. > + */ > +#if IS_ENABLED(CONFIG_OVERLAY_FS) This is crap - it should be handled in fs/Makefile, not with IS_ENABLED. > +#include <linux/overlay_util.h> > +#include <linux/fs.h> > +#include <linux/file.h> > +#include "internal.h" > + > +static bool overlay_file_consistent(struct file *file) > +{ > + return d_real_inode(file->f_path.dentry) == file_inode(file); > +} > + > +ssize_t overlay_read_iter(struct file *file, struct kiocb *kio, > + struct iov_iter *iter) > +{ > + ssize_t ret; > + > + if (likely(overlay_file_consistent(file))) > + return file->f_op->read_iter(kio, iter); > + > + file = filp_clone_open(file); > + if (IS_ERR(file)) > + return PTR_ERR(file); > + > + ret = vfs_iter_read(file, iter, &kio->ki_pos); > + fput(file); You do realize that a bunch of such calls will breed arseloads of struct file, right? Freeing is delayed... > +static inline bool is_overlay_file(struct file *file) > +{ > + return IS_ENABLED(CONFIG_OVERLAY_FS) && file->f_mode & FMODE_OVERLAY; > +} > + > static inline ssize_t call_read_iter(struct file *file, struct kiocb *kio, > struct iov_iter *iter) > { > + if (unlikely(is_overlay_file(file))) > + return overlay_read_iter(file, kio, iter); > + > return file->f_op->read_iter(kio, iter); > } 1) that IS_ENABLED is fairly pointless and it's not obvious that nobody else will use that flag 2) what that check should include is overlay_file_consistent(), with no method call in overlay_read_iter(). 3) anything that does a plenty of calls of kernel_read() is going to be very unpleasantly surprised by the effects of that thing.
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