linux-ext4 - Re: generic quota vs xfs quota

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Message-ID: <20180426172246.GB5965@thunk.org>
Date:   Thu, 26 Apr 2018 13:22:46 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Liu Bo <obuil.liubo@...il.com>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: generic quota vs xfs quota

On Thu, Apr 26, 2018 at 04:16:08PM +0800, Liu Bo wrote:
> 
> and ext4 ->statfs() only displays dqb_curspace while xfs ->statfs()
> displays both,

I'm not sure what you are asking.  statfs(2) has nothing to do with
quota support.

As far as reserved delayed allocation blocks is concerned, ext4
deducts the space from the available space in the file system and from
the user's quota when the user writes to a file and when the space is
reserved for delayed allocation.  My understanding is that xfs does
the same thing.

Also, the linux native quota predates XFS's quota system (which came
from Irix), so there are some subtle differences between them,
although we do try keep things as consistent as possible.  For
example, only recently we added support for project quota to ext4,
which is something that used to be XFS only.  However, there is a lot
of complexity in terms of the low-level system interfaces for quota.
Most of this is hidden in the quota-tools userspace package.

Does this help?

						- Ted