linux-ext4 - Re: [v8 2/5] ext4: adds project ID support

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Date:	Mon, 12 Jan 2015 18:01:22 +0100
From:	Jan Kara <jack@...e.cz>
To:	Dave Chinner <david@...morbit.com>
Cc:	Jan Kara <jack@...e.cz>, Andreas Dilger <adilger@...ger.ca>,
	Li Xi <pkuelelixi@...il.com>,
	Linux Filesystem Development List 
	<linux-fsdevel@...r.kernel.org>,
	ext4 development <linux-ext4@...r.kernel.org>,
	linux-api@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
	Al Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	Dmitry Monakhov <dmonakhov@...nvz.org>
Subject: Re: [v8 2/5] ext4: adds project ID support

On Sat 10-01-15 10:46:27, Dave Chinner wrote:
> On Fri, Jan 09, 2015 at 10:47:58AM +0100, Jan Kara wrote:
> > On Thu 08-01-15 15:20:21, Andreas Dilger wrote:
> > > On Jan 8, 2015, at 1:26 AM, Jan Kara <jack@...e.cz> wrote:
> > > > On Tue 09-12-14 13:22:25, Li Xi wrote:
> > > >> This patch adds a new internal field of ext4 inode to save project
> > > >> identifier. Also a new flag EXT4_INODE_PROJINHERIT is added for
> > > >> inheriting project ID from parent directory.
> > > >  I have noticed one thing you apparently changed in v7 of the patch set.
> > > > See below.
> > > > 
> > > >> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> > > >> index 29c43e7..8bd1da9 100644
> > > >> --- a/fs/ext4/ext4.h
> > > >> +++ b/fs/ext4/ext4.h
> > > >> @@ -377,16 +377,18 @@ struct flex_groups {
> > > >> #define EXT4_EA_INODE_FL	        0x00200000 /* Inode used for large EA */
> > > >> #define EXT4_EOFBLOCKS_FL		0x00400000 /* Blocks allocated beyond EOF */
> > > >> #define EXT4_INLINE_DATA_FL		0x10000000 /* Inode has inline data. */
> > > >> +#define EXT4_PROJINHERIT_FL		FS_PROJINHERIT_FL /* Create with parents projid */
> > > >  How did FS_PROJINHERIT_FL get here? There used to be 0x20000000 in older
> > > > version of the patch set which is correct - this definition is defining
> > > > ext4 on-disk format. As such it is an ext4 specific flag and should be
> > > > definined to a fixed constant independed of any other filesystem. It seems
> > > > you are somewhat mixing what is an on-disk format flag value and what is a
> > > > flag value passed from userspace. These two may be different things and
> > > > you need to convert between the values when getting / setting flags...
> > > 
> > > Currently the EXT4_*_FL and FS_*_FL values are all identical, and there
> > > is no reason to change that before it is actually needed.  Since the
> > > FS_PROJINHERIT_FL is used via chattr/lsattr from userspace, this value
> > > must also be kept the same in the future to avoid API breakage, so there
> > > is no reason to worry about incompatibilities.
> >   Agreed. I was somewhat worried about having on-disk flag defined through
> > the external non-ext4 define but you are right that neither can really
> > change once we ship a kernel with it.
> > 
> > > See also the [v8 5/5] patch, which is changing the EXT4_*_FL values to
> > > use FS_*_FL constants, where applicable, so that it is more clear that
> > > these values need to be the same.
> >   OK, I've missed that. So if things will be consistent again, I'm fine
> > with the change.
> 
> Except that I NACK'd that change (i.e patch 4/5) because it's out of
> scope of a "support project quota" patchset. not to mention that it
> is broken because it exhausts the flags space with ext4 specific
> flags and prevents future expansion of the ioctl structure.
  I agree with your objections from that review (which is why I didn't
reply to that email since I didn't have more to say).

> Any extension to the ioctl needs to be done in a spearate patch set,
> with separate justification. This patch set should only implement
> the very minimum needed to use the project quota ioctl flags....
  Agreed. I was just saying that I have nothing against defining ext4 flag
values using FS_*_FL where possible.

							Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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