From: Miklos Szeredi <miklos@szeredi.hu>
To: Randy Dunlap <rdunlap@infradead.org>
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 v2 23/35] ovl: copy-up on MAP_SHARED
Date: Tue, 8 May 2018 17:03:49 +0200 [thread overview]
Message-ID: <CAJfpegu-MDi21vBYnyqRBKG40ugPNDY9YUZmkmQ7A5pFp=ak0Q@mail.gmail.com> (raw)
In-Reply-To: <8f464b5f-a479-6bfe-3abf-b2ed6efe5eb6@infradead.org>
On Mon, May 7, 2018 at 9:28 PM, Randy Dunlap <rdunlap@infradead.org> wrote:
> On 05/07/2018 01:37 AM, Miklos Szeredi wrote:
>> A corner case of a corner case is when
>>
>> - file opened for O_RDONLY
>> - which is then memory mapped SHARED
>> - file opened for O_WRONLY
>> - contents modified
>> - contents read back though the shared mapping
>>
>> Unfortunately it looks very difficult to do anything about the established
>> shared map after the file is copied up.
>>
>> Instead, when a read-only file is mapped shared, copy up the file before
>> actually doing the map. This may result in unnecessary copy-ups (but so
>> may copy-up on open(O_RDWR) for exampe).
>
> for example).
>
>>
>> We can revisit this later if it turns out to be a performance problem in
>> real life.
>>
>> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
>> ---
>> fs/overlayfs/Kconfig | 21 +++++++++++++++++++++
>> fs/overlayfs/file.c | 22 ++++++++++++++++++++++
>> fs/overlayfs/overlayfs.h | 7 +++++++
>> fs/overlayfs/ovl_entry.h | 1 +
>> fs/overlayfs/super.c | 22 ++++++++++++++++++++++
>> 5 files changed, 73 insertions(+)
>>
>> diff --git a/fs/overlayfs/Kconfig b/fs/overlayfs/Kconfig
>> index 17032631c5cf..991c0a5a0e00 100644
>> --- a/fs/overlayfs/Kconfig
>> +++ b/fs/overlayfs/Kconfig
>> @@ -103,3 +103,24 @@ config OVERLAY_FS_XINO_AUTO
>> For more information, see Documentation/filesystems/overlayfs.txt
>>
>> If unsure, say N.
>> +
>> +config OVERLAY_FS_COPY_UP_SHARED
>> + bool "Overlayfs: copy up when mapping a file shared"
>
> a shared file" ??
This is referring to MAP_SHARED flag of mmap(). So it's the mapping
that is shared, not the file.
>
>> + default n
>> + depends on OVERLAY_FS
>> + help
>> + If this option is enabled then on mapping a file with MAP_SHARED
>> + overlayfs copies up the file in anticipation of it being modified (just
>> + like we copy up the file on O_WRONLY and O_RDWR in anticipation of
>> + modification). This does not interfere with shared library loading, as
>> + that uses MAP_PRIVATE. But there might be use cases out there where
>> + this impacts performance and disk usage.
>> +
>> + This just selects the default, the feature can also be enabled or
>> + disabled in the running kernel or individually on each overlay mount.
>> +
>> + To get maximally standard compliant behavior, enable this option.
>> +
>> + To get a maximally backward compatible kernel, disable this option.
>> +
>> + If unsure, say N.
>
> For Kconfig (coding-style.rst):
> Lines under a ``config`` definition are indented with one tab, while help text
> is indented an additional two spaces.
Not sure what went wrong there. Fixed now.
Thanks,
Miklos
next prev parent reply other threads:[~2018-05-08 15:03 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-07 8:37 [PATCH v2 00/35] overlayfs: stack file operations Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 01/35] vfs: add path_open() Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 02/35] vfs: optionally don't account file in nr_files Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 03/35] vfs: add f_op->pre_mmap() Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 04/35] vfs: export vfs_ioctl() to modules Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 05/35] vfs: export vfs_dedupe_file_range_one() " Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 06/35] ovl: copy up times Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 07/35] ovl: copy up inode flags Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 08/35] Revert "Revert "ovl: get_write_access() in truncate"" Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 09/35] ovl: copy up file size as well Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 10/35] ovl: deal with overlay files in ovl_d_real() Miklos Szeredi
2018-05-07 13:17 ` Vivek Goyal
2018-05-07 8:37 ` [PATCH v2 11/35] ovl: stack file ops Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 12/35] ovl: add helper to return real file Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 13/35] ovl: add ovl_read_iter() Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 14/35] ovl: add ovl_write_iter() Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 15/35] ovl: add ovl_fsync() Miklos Szeredi
2018-05-08 5:14 ` Amir Goldstein
2018-05-08 14:57 ` Miklos Szeredi
2018-05-08 15:02 ` Amir Goldstein
2018-05-07 8:37 ` [PATCH v2 16/35] ovl: add ovl_mmap() Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 17/35] ovl: add ovl_fallocate() Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 18/35] ovl: add lsattr/chattr support Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 19/35] ovl: add ovl_fiemap() Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 20/35] ovl: add O_DIRECT support Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 21/35] ovl: add reflink/copyfile/dedup support Miklos Szeredi
2018-05-07 20:43 ` Darrick J. Wong
2018-05-08 14:13 ` Miklos Szeredi
2018-05-08 14:38 ` Darrick J. Wong
2018-05-07 8:37 ` [PATCH v2 22/35] vfs: don't open real Miklos Szeredi
2018-05-07 10:27 ` Amir Goldstein
2018-05-07 10:29 ` Miklos Szeredi
2018-05-11 18:54 ` Vivek Goyal
2018-05-11 19:42 ` Vivek Goyal
2018-05-14 13:58 ` Vivek Goyal
2018-05-15 20:42 ` Vivek Goyal
2018-05-14 14:03 ` Daniel Walsh
2018-05-07 8:37 ` [PATCH v2 23/35] ovl: copy-up on MAP_SHARED Miklos Szeredi
2018-05-07 19:28 ` Randy Dunlap
2018-05-08 15:03 ` Miklos Szeredi [this message]
2018-05-07 8:37 ` [PATCH v2 24/35] vfs: simplify dentry_open() Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 25/35] Revert "ovl: fix may_write_real() for overlayfs directories" Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 26/35] Revert "ovl: don't allow writing ioctl on lower layer" Miklos Szeredi
2018-05-07 8:37 ` [PATCH v2 27/35] vfs: fix freeze protection in mnt_want_write_file() for overlayfs Miklos Szeredi
2018-05-07 8:38 ` [PATCH v2 28/35] Revert "ovl: fix relatime for directories" Miklos Szeredi
2018-05-07 8:38 ` [PATCH v2 29/35] Revert "vfs: update ovl inode before relatime check" Miklos Szeredi
2018-05-07 8:38 ` [PATCH v2 30/35] Revert "vfs: add flags to d_real()" Miklos Szeredi
2018-05-07 8:38 ` [PATCH v2 31/35] Revert "vfs: do get_write_access() on upper layer of overlayfs" Miklos Szeredi
2018-05-07 8:38 ` [PATCH v2 32/35] Partially revert "locks: fix file locking on overlayfs" Miklos Szeredi
2018-05-08 15:15 ` Jeff Layton
2018-05-07 8:38 ` [PATCH v2 33/35] Revert "fsnotify: support overlayfs" Miklos Szeredi
2018-05-07 8:38 ` [PATCH v2 34/35] vfs: remove open_flags from d_real() Miklos Szeredi
2018-05-07 8:38 ` [PATCH v2 35/35] ovl: fix documentation of non-standard behavior Miklos Szeredi
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