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From: Miklos Szeredi <miklos@szeredi.hu>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Christoph Hellwig <hch@infradead.org>,
	Miklos Szeredi <mszeredi@redhat.com>,
	overlayfs <linux-unionfs@vger.kernel.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-xfs <linux-xfs@vger.kernel.org>,
	ocfs2-devel@oss.oracle.com
Subject: Re: [PATCH 01/39] vfs: dedpue: return loff_t
Date: Mon, 18 Jun 2018 22:08:54 +0200	[thread overview]
Message-ID: <CAJfpeguMN4t80cUCxyTxeHW9_Hb61DzDRPzTa371dc2YQRHuZQ@mail.gmail.com> (raw)
In-Reply-To: <20180606150905.GC9426@magnolia>

On Wed, Jun 6, 2018 at 5:09 PM, Darrick J. Wong <darrick.wong@oracle.com> wrote:
> On Tue, Jun 05, 2018 at 10:33:22AM +0200, Miklos Szeredi wrote:
>> On Mon, Jun 4, 2018 at 10:43 AM, Christoph Hellwig <hch@infradead.org> wrote:
>> > On Tue, May 29, 2018 at 04:43:01PM +0200, Miklos Szeredi wrote:
>> >> f_op->dedupe_file_range() gets a u64 length to dedup and returns an ssize_t
>> >> actual length deduped.  This breaks badly on 32bit archs since the returned
>> >> length will be truncated and possibly overflow into the sign bit (xfs and
>> >> ocfs2 are affected, btrfs limits actual length to 16MiB).
>> >
>> > Can we just make it return 0 vs errno?  The only time we return
>> > a different length than the one passed in is due to the btrfs cap.
>> >
>> > Given that this API started out on btrfs we should just do the cap
>> > everywhere to not confuse userspace.
>>
>> And that's a completely arbitrary cap; sure btrfs started out with
>> that, but there's no fundamental reason for that becoming the global
>> limit.  Xfs now added a different, larger limit, so based on what
>> reason should that limit be reduced?
>>
>> I don't care either way, but at this stage I'm not going to change
>> this patch, unless there's a very good reason to do so, because if I
>> do someone will come and suggest another improvement, ad-infinitum...
>
> I think we should hoist the MAX_RW_COUNT/2 limit to the VFS helpers
> since afaict we generally cap max IO per call at MAX_RW_COUNT.

I don't quite get it.   That MAX_RW_COUNT is to protect against
overflows in signed int.

Here we have a 64bit interface, so that's irrelevant, we can invent
any cap we want.  Lets choose our favorite bike shed size.  Mine is
1G.  But if that turns out too limiting it can be raised arbitrarily
later.

>  (I
> probably should've capped ocfs2 back when I did xfs, but forgot).  If
> btrfs wants to keep their lower (16M) limit then they're free to do so;
> the interface documentation allows for this.  One of the btrfs
> developers seems to be working on a patch series to raise the limit[1]
> anyway.

Yep, that got upstreamed now.  Which is good, we can just return zero
or error from ->dedupe_file_range() and be done with that.

Thanks,
Miklos

  reply	other threads:[~2018-06-18 20:08 UTC|newest]

Thread overview: 83+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-29 14:43 [PATCH 00/39] overlayfs: stack file operations Miklos Szeredi
2018-05-29 14:43 ` [PATCH 01/39] vfs: dedpue: return loff_t Miklos Szeredi
2018-06-04  8:43   ` Christoph Hellwig
2018-06-05  8:33     ` Miklos Szeredi
2018-06-06 15:09       ` Darrick J. Wong
2018-06-18 20:08         ` Miklos Szeredi [this message]
2018-05-29 14:43 ` [PATCH 02/39] vfs: dedupe: rationalize args Miklos Szeredi
2018-06-06 15:02   ` Darrick J. Wong
2018-05-29 14:43 ` [PATCH 03/39] vfs: dedupe: extract helper for a single dedup Miklos Szeredi
2018-05-29 15:41   ` Amir Goldstein
2018-05-29 16:04     ` Amir Goldstein
2018-06-04  8:44   ` Christoph Hellwig
2018-05-29 14:43 ` [PATCH 04/39] vfs: add path_open() Miklos Szeredi
2018-06-04  8:46   ` Christoph Hellwig
2018-06-10  4:36     ` Al Viro
2018-05-29 14:43 ` [PATCH 05/39] vfs: optionally don't account file in nr_files Miklos Szeredi
2018-06-04  8:47   ` Christoph Hellwig
2018-06-04  8:57     ` Miklos Szeredi
2018-06-10  4:41   ` Al Viro
2018-05-29 14:43 ` [PATCH 06/39] vfs: add f_op->pre_mmap() Miklos Szeredi
2018-06-04  8:48   ` Christoph Hellwig
2018-06-05 11:36     ` Miklos Szeredi
2018-05-29 14:43 ` [PATCH 07/39] vfs: export vfs_ioctl() to modules Miklos Szeredi
2018-06-04  8:49   ` Christoph Hellwig
2018-06-10  4:57     ` Al Viro
2018-06-11  7:19       ` Miklos Szeredi
2018-06-11 16:24         ` Christoph Hellwig
2018-06-19 14:04           ` Miklos Szeredi
2018-06-19 14:24             ` Christoph Hellwig
2018-06-19 14:34               ` Miklos Szeredi
2018-06-19 14:54                 ` Al Viro
2018-05-29 14:43 ` [PATCH 08/39] vfs: export vfs_dedupe_file_range_one() " Miklos Szeredi
2018-05-29 14:43 ` [PATCH 09/39] ovl: copy up times Miklos Szeredi
2018-05-29 14:43 ` [PATCH 10/39] ovl: copy up inode flags Miklos Szeredi
2018-05-29 14:43 ` [PATCH 11/39] Revert "Revert "ovl: get_write_access() in truncate"" Miklos Szeredi
2018-05-29 14:43 ` [PATCH 12/39] ovl: copy up file size as well Miklos Szeredi
2018-05-29 14:43 ` [PATCH 13/39] ovl: deal with overlay files in ovl_d_real() Miklos Szeredi
2018-05-29 14:43 ` [PATCH 14/39] ovl: stack file ops Miklos Szeredi
2018-06-10  4:13   ` Al Viro
2018-06-11  7:09     ` Miklos Szeredi
2018-06-12  2:29       ` Al Viro
2018-06-12  2:40         ` Al Viro
2018-06-12  9:24           ` Miklos Szeredi
2018-06-12 18:24             ` Al Viro
2018-06-12 18:31               ` Al Viro
2018-06-13  9:21                 ` Miklos Szeredi
2018-06-15  5:47                   ` Al Viro
2018-06-18 11:50                     ` Miklos Szeredi
2018-06-13 11:56               ` J. R. Okajima
2018-05-29 14:43 ` [PATCH 15/39] ovl: add helper to return real file Miklos Szeredi
2018-06-10  5:42   ` Al Viro
2018-06-11  8:11     ` Miklos Szeredi
2018-05-29 14:43 ` [PATCH 16/39] ovl: add ovl_read_iter() Miklos Szeredi
2018-05-29 14:43 ` [PATCH 17/39] ovl: add ovl_write_iter() Miklos Szeredi
2018-05-29 14:43 ` [PATCH 18/39] ovl: add ovl_fsync() Miklos Szeredi
2018-05-29 14:43 ` [PATCH 19/39] ovl: add ovl_mmap() Miklos Szeredi
2018-06-10  5:24   ` Al Viro
2018-06-11  7:58     ` Miklos Szeredi
2018-05-29 14:43 ` [PATCH 20/39] ovl: add ovl_fallocate() Miklos Szeredi
2018-05-29 14:43 ` [PATCH 21/39] ovl: add lsattr/chattr support Miklos Szeredi
2018-05-29 14:43 ` [PATCH 22/39] ovl: add ovl_fiemap() Miklos Szeredi
2018-05-29 14:43 ` [PATCH 23/39] ovl: add O_DIRECT support Miklos Szeredi
2018-06-10  5:31   ` Al Viro
2018-06-11  8:08     ` Miklos Szeredi
2018-05-29 14:43 ` [PATCH 24/39] ovl: add reflink/copyfile/dedup support Miklos Szeredi
2018-05-29 14:43 ` [PATCH 25/39] vfs: don't open real Miklos Szeredi
2018-05-29 14:43 ` [PATCH 26/39] ovl: copy-up on MAP_SHARED Miklos Szeredi
2018-05-29 14:43 ` [PATCH 27/39] ovl: obsolete "check_copy_up" module option Miklos Szeredi
2018-05-29 15:13   ` Amir Goldstein
2018-05-30  8:26     ` Miklos Szeredi
2018-05-29 14:43 ` [PATCH 28/39] ovl: fix documentation of non-standard behavior Miklos Szeredi
2018-05-29 14:43 ` [PATCH 29/39] vfs: simplify dentry_open() Miklos Szeredi
2018-05-29 14:43 ` [PATCH 30/39] Revert "ovl: fix may_write_real() for overlayfs directories" Miklos Szeredi
2018-05-29 14:43 ` [PATCH 31/39] Revert "ovl: don't allow writing ioctl on lower layer" Miklos Szeredi
2018-05-29 14:43 ` [PATCH 32/39] vfs: fix freeze protection in mnt_want_write_file() for overlayfs Miklos Szeredi
2018-06-04  8:50   ` Christoph Hellwig
2018-05-29 14:43 ` [PATCH 33/39] Revert "ovl: fix relatime for directories" Miklos Szeredi
2018-05-29 14:43 ` [PATCH 34/39] Revert "vfs: update ovl inode before relatime check" Miklos Szeredi
2018-05-29 14:43 ` [PATCH 35/39] Revert "vfs: add flags to d_real()" Miklos Szeredi
2018-05-29 14:43 ` [PATCH 36/39] Revert "vfs: do get_write_access() on upper layer of overlayfs" Miklos Szeredi
2018-05-29 14:43 ` [PATCH 37/39] Partially revert "locks: fix file locking on overlayfs" Miklos Szeredi
2018-05-29 14:43 ` [PATCH 38/39] Revert "fsnotify: support overlayfs" Miklos Szeredi
2018-05-29 14:43 ` [PATCH 39/39] vfs: remove open_flags from d_real() Miklos Szeredi

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