From: Miklos Szeredi <miklos@szeredi.hu>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Miklos Szeredi <mszeredi@redhat.com>,
overlayfs <linux-unionfs@vger.kernel.org>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 15/39] ovl: add helper to return real file
Date: Mon, 11 Jun 2018 10:11:42 +0200 [thread overview]
Message-ID: <CAJfpegvoF=kMH1qx3nbegDAEcnSYQgGDiDOKxTiwq7rsR4hbog@mail.gmail.com> (raw)
In-Reply-To: <20180610054156.GP30522@ZenIV.linux.org.uk>
On Sun, Jun 10, 2018 at 7:42 AM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> On Tue, May 29, 2018 at 04:43:15PM +0200, Miklos Szeredi wrote:
>> In the common case we can just use the real file cached in
>> file->private_data. There are two exceptions:
>>
>> 1) File has been copied up since open: in this unlikely corner case just
>> use a throwaway real file for the operation. If ever this becomes a
>> perfomance problem (very unlikely, since overlayfs has been doing most fine
>> without correctly handling this case at all), then we can deal with that by
>> updating the cached real file.
>
> See the ovl_mmap() problem. FWIW, I would probably suggest something along
> the lines of
> ->private_data either points to struct file, or is 1 | address of
> 2-element array of struct file *
> odd value => mask bit 0 away, cast to struct file ** and dereference
> even value and it's still in the right layer => use that
> even value and it is in the wrong layer =>
> allocate a two-pointer array
> open in the right layer
> stick that into array[0] and original - into array[1]
> cmpxchg array | 1 into ->private_data
> if that succeeds
> return array[0]
> else
> fput array[0], free array, then use the value returned
> by cmpxchg - mask bit 0 away, cast and dereference
Iff we really need that complexity, then yes, that's a nice solution.
But I think we don't: see incremental posted for ->mmap() issue + for
plain I/O we don't really care about this case, since it happens so
rarely. Maybe later...
Thanks,
Miklos
next prev parent reply other threads:[~2018-06-11 8:11 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
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 [this message]
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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