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From: Benjamin Thery <benjamin.thery@bull.net>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>,
	Greg Kroah-Hartman <gregkh@suse.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Tejun Heo <htejun@gmail.com>,
	linux-kernel@vger.kernel.org, Al Viro <viro@ftp.linux.org.uk>,
	Linux Containers <containers@lists.osdl.org>,
	"Serge E. Hallyn" <serue@us.ibm.com>,
	Daniel Lezcano <dlezcano@fr.ibm.com>
Subject: Re: [PATCH 01/11] sysfs: Support for preventing unmounts.
Date: Thu, 19 Jun 2008 10:54:49 +0200	[thread overview]
Message-ID: <485A1ED9.5040704@bull.net> (raw)
In-Reply-To: <m18wx2o638.fsf@frodo.ebiederm.org>

Eric W. Biederman wrote:
> Dave Hansen <dave@linux.vnet.ibm.com> writes:
> 
>> On Wed, 2008-06-18 at 19:07 +0200, Benjamin Thery wrote:
>>> To support mounting multiple instances of sysfs occassionally I
>>> need to walk through all of the currently present sysfs super blocks.
>> I know you may have addressed this before, but I forgot and it didn't
>> make it into the changelogs.
>>
>> Why are you doing this again?  It seems like an awfully blunt
>> instrument.  
> 
> So the fundamentals.
> - The data in sysfs fundamentally changes behind the back of the
>   VFS and we need to keep the VFS in sync.  Essentially this is the
>   distributed filesystem problem.
> 
> - In particular for sysfs_rename and sysfs_move_dir we need to support finding
>   the dcache entries and calling d_move.  So that the dcache does not
>   get into an inconsistent state.  Timeouts and invalidates like NFS
>   uses are to be  avoided if at all possible.
> 
> - Coming through the vfs we are guaranteed that the filesystem will
>   not be unmounted while we have a reference on a dentry, and with
>   multiple mounts we do not get that guarantee.  Therefore to get that
>   guarantee for all of the superblocks we need the blunt instrument.
> 
> - Since mount/unmount are rare blocking them is no big deal.
> 
> I believe any distributed filesystem that is together enough to tell
> us about renames (so we can update the dcache) instead of doing the
> NFS timeout will need the ability to block mount/unmount while it is
> executing d_move.
> 
> Currently sysfs does not need to block mounts only because we perform
> an internal mount and then never unmount sysfs.

Thanks Eric for detailing this.
I think you explained it in much better way than I could do.
You're the author of the patch after all ;-)

  Benjamin

> 
> Eric
> 
> 


-- 
B e n j a m i n   T h e r y  - BULL/DT/Open Software R&D

    http://www.bull.com

  reply	other threads:[~2008-06-19  8:59 UTC|newest]

Thread overview: 138+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-06-18 17:07 [PATCH 00/11] sysfs tagged directories V6 Benjamin Thery
2008-06-18 17:07 ` [PATCH 01/11] sysfs: Support for preventing unmounts Benjamin Thery
2008-06-18 17:44   ` Dave Hansen
2008-06-18 20:12     ` Eric W. Biederman
2008-06-19  8:54       ` Benjamin Thery [this message]
2008-06-19 16:32       ` Dave Hansen
2008-06-19 20:19         ` Benjamin Thery 
2008-06-18 17:07 ` [PATCH 02/11] sysfs: sysfs_get_dentry add a sb parameter Benjamin Thery
2008-06-18 17:07 ` [PATCH 03/11] sysfs: Implement __sysfs_get_dentry Benjamin Thery
2008-06-18 17:08 ` [PATCH 04/11] sysfs: Rename Support multiple superblocks Benjamin Thery
2008-06-18 17:08 ` [PATCH 05/11] sysfs: sysfs_chmod_file handle " Benjamin Thery
2008-06-22  4:46   ` Tejun Heo
2008-06-23 21:42     ` Daniel Lezcano
2008-06-24  4:45       ` Tejun Heo
2008-06-24 10:39         ` Daniel Lezcano
2008-06-24 13:37         ` Daniel Lezcano
2008-06-25 12:31           ` Tejun Heo
2008-06-18 17:08 ` [PATCH 06/11] sysfs: Implement sysfs tagged directory support Benjamin Thery
2008-06-23  2:05   ` Tejun Heo
2008-06-26 20:21     ` Eric W. Biederman
2008-06-29  3:51       ` Tejun Heo
2008-06-30 18:56         ` Eric W. Biederman
2008-06-30 21:44           ` Serge E. Hallyn
2008-07-01  7:50             ` Eric W. Biederman
2008-07-01  6:47           ` Tejun Heo
2008-07-01  9:20             ` Eric W. Biederman
2008-07-01 10:30               ` Tejun Heo
2008-07-01 12:30                 ` Eric W. Biederman
2008-07-02  3:24                   ` Tejun Heo
2008-07-02  3:53                     ` Eric W. Biederman
2008-07-02  4:37                       ` Tejun Heo
2008-07-02 16:49                         ` Eric W. Biederman
2008-07-03  0:15                           ` Greg KH
2008-07-03  3:18                           ` Tejun Heo
2008-07-03  5:11                             ` Eric W. Biederman
2008-07-03 10:56                               ` Daniel Lezcano
2008-07-03 12:27                                 ` Eric W. Biederman
2008-07-03 12:37                                   ` Benjamin Thery
2008-07-03 19:57                                     ` Eric W. Biederman
2008-07-03 12:55                                   ` Daniel Lezcano
2008-07-03 15:58                                   ` Tejun Heo
2008-07-03 18:29                                     ` Daniel Lezcano
2008-07-03 20:08                                     ` Eric W. Biederman
2008-07-04  0:48                                     ` [PATCH 00/15] sysfs support for namespaces Eric W. Biederman
2008-07-04  1:05                                       ` [PATCH 01/15] kobject: Cleanup kobject_rename and !CONFIG_SYSFS Eric W. Biederman
2008-07-04  1:07                                         ` [PATCH 02/15] sysfs: Support for preventing unmounts Eric W. Biederman
2008-07-04  1:08                                           ` [PATCH 03/15] sysfs: sysfs_get_dentry add a sb parameter Eric W. Biederman
2008-07-04  1:09                                             ` [PATCH 04/15] sysfs: Implement __sysfs_get_dentry Eric W. Biederman
2008-07-04  1:10                                               ` [PATCH 05/15] sysfs: Rename Support multiple superblocks Eric W. Biederman
2008-07-04  1:11                                                 ` [PATCH 06/15] Introduce sysfs_sd_setattr and fix sysfs_chmod Eric W. Biederman
2008-07-04  1:13                                                   ` [PATCH 07/15] sysfs: sysfs_chmod_file handle multiple superblocks Eric W. Biederman
2008-07-04  1:14                                                     ` [PATCH 08/15] sysfs: Make sysfs_mount static once again Eric W. Biederman
2008-07-04  1:16                                                       ` [PATCH 09/15] sysfs: Implement sysfs tagged directory support Eric W. Biederman
2008-07-04  1:17                                                         ` [PATCH 10/15] sysfs: Merge sysfs_rename_dir and sysfs_move_dir Eric W. Biederman
2008-07-04  1:18                                                           ` [PATCH 11/15] sysfs: Implement sysfs_delete_link and sysfs_rename_link Eric W. Biederman
2008-07-04  1:20                                                             ` [PATCH 12/15] driver core: Implement tagged directory support for device classes Eric W. Biederman
2008-07-04  1:21                                                               ` [PATCH 13/15] Revert "netns: Fix device renaming for sysfs" Eric W. Biederman
2008-07-04  1:22                                                                 ` [PATCH 14/15] netns: Enable tagging for net_class directories in sysfs Eric W. Biederman
2008-07-04  1:23                                                                   ` [PATCH 15/15] sysfs: user namespaces: fix bug with clone(CLONE_NEWUSER) with fairsched Eric W. Biederman
2008-07-04  7:50                                                               ` [PATCH 12/15] driver core: Implement tagged directory support for device classes Tejun Heo
2008-07-04 13:31                                                                 ` Eric W. Biederman
2008-07-04 13:57                                                                   ` Tejun Heo
2008-07-04 16:12                                                                     ` Greg KH
2008-07-04 21:49                                                                       ` Eric W. Biederman
2008-07-14  1:54                                                                       ` Eric W. Biederman
2008-07-16  3:25                                                                         ` Tejun Heo
2008-07-16  5:41                                                                           ` Eric W. Biederman
2008-07-16  5:50                                                                             ` Tejun Heo
2008-07-16  6:32                                                                               ` Eric W. Biederman
2008-07-16  6:48                                                                                 ` Tejun Heo
2008-07-16  7:02                                                                                   ` Tejun Heo
2008-07-16 19:07                                                                                     ` Eric W. Biederman
2008-07-16 21:09                                                                                   ` Eric W. Biederman
2008-07-17 23:08                                                                           ` Greg KH
2008-07-18 12:41                                                                             ` Tejun Heo
2008-07-18 18:49                                                                               ` Greg KH
2008-07-18 20:19                                                                                 ` Eric W. Biederman
2008-07-19  1:07                                                                                 ` Tejun Heo
2008-08-03  6:59                                                                                 ` Eric W. Biederman
2008-09-11 12:45                                                                                   ` Jiri Slaby
2008-09-11 13:05                                                                                     ` Benjamin Thery
2008-09-12  6:32                                                                                       ` Jiri Slaby
2008-07-04 22:00                                                                     ` Eric W. Biederman
2008-08-20  2:17                                                         ` [PATCH 09/15] sysfs: Implement sysfs tagged directory support Greg KH
2008-08-20  6:58                                                           ` Eric W. Biederman
2008-08-21  6:31                                                           ` [PATCH 0/8] sysfs namespace support Eric W. Biederman
2008-08-21  6:33                                                             ` [PATCH 1/8] sysfs: Implement sysfs tagged directory support Eric W. Biederman
2008-08-21  6:34                                                               ` [PATCH 2/8] sysfs: Merge sysfs_rename_dir and sysfs_move_dir Eric W. Biederman
2008-08-21  6:35                                                                 ` [PATCH 3/8] sysfs: Implement sysfs_delete_link and sysfs_rename_link Eric W. Biederman
2008-08-21  6:36                                                                   ` [PATCH 5/8] sysfs: Remove sysfs_create_link_nowarn Eric W. Biederman
2008-08-21  6:38                                                                     ` [PATCH 6/8] Revert "netns: Fix device renaming for sysfs" Eric W. Biederman
2008-08-21  6:39                                                                       ` [PATCH 7/8] netns: Enable tagging for net_class directories in sysfs Eric W. Biederman
2008-08-21  6:40                                                                         ` [PATCH 8/8] sysfs: user namespaces: fix bug with clone(CLONE_NEWUSER) with fairsched Eric W. Biederman
2008-08-21  6:47                                                                         ` [PATCH 7/8] netns: Enable tagging for net_class directories in sysfs David Miller
2008-08-21  6:47                                                                       ` [PATCH 6/8] Revert "netns: Fix device renaming for sysfs" David Miller
2008-08-21  6:37                                                                   ` [PATCH 4/8] driver core: Implement tagged directory support for device classes Eric W. Biederman
2008-08-27 15:18                                                               ` [PATCH 1/8] sysfs: Implement sysfs tagged directory support Benjamin Thery
2008-09-02 13:54                                                                 ` Mark Ryden
2008-09-02 14:03                                                                   ` Benjamin Thery
2008-09-02 17:01                                                                     ` Greg KH
2008-09-04  5:33                                                                       ` David Shwatrz
2008-09-04  6:44                                                                         ` Benjamin Thery
2008-09-08 18:39                                                                           ` Mark Ryden
2008-10-07 16:39                                                                           ` Mark Ryden
2008-10-07 16:48                                                                             ` Greg KH
2008-10-07 20:31                                                                               ` Eric W. Biederman
2008-10-07 21:09                                                                                 ` Greg KH
2008-10-07 22:27                                                                                   ` Eric W. Biederman
2008-10-08 13:00                                                                                     ` Christoph Hellwig
2008-10-14  3:20                                                                                       ` Eric W. Biederman
2008-10-07 16:52                                                                             ` Daniel Lezcano
2008-08-21  6:37                                                             ` [PATCH 0/8] sysfs namespace support David Miller
2008-07-04  6:44                                                       ` [PATCH 08/15] sysfs: Make sysfs_mount static once again Tejun Heo
2008-07-04  6:44                                                     ` [PATCH 07/15] sysfs: sysfs_chmod_file handle multiple superblocks Tejun Heo
2008-07-04  6:40                                                   ` [PATCH 06/15] Introduce sysfs_sd_setattr and fix sysfs_chmod Tejun Heo
2008-07-04  6:33                                         ` [PATCH 01/15] kobject: Cleanup kobject_rename and !CONFIG_SYSFS Tejun Heo
2008-07-04  1:27                                       ` [PATCH 00/15] sysfs support for namespaces Eric W. Biederman
2008-07-06  4:42                                       ` Eric W. Biederman
2008-07-07 11:41                                         ` Cornelia Huck
2008-07-07 12:22                                           ` Eric W. Biederman
2008-06-18 17:08 ` [PATCH 07/11] sysfs: Implement sysfs_delete_link and sysfs_rename_link Benjamin Thery
2008-06-23  2:13   ` Tejun Heo
2008-06-26 20:24     ` Eric W. Biederman
2008-06-29  3:35       ` Tejun Heo
2008-06-30  3:02         ` Eric W. Biederman
2008-06-18 17:08 ` [PATCH 08/11] driver core: Implement tagged directory support for device classes Benjamin Thery
2008-06-18 17:08 ` [PATCH 09/11] sysfs: add sysfs_ns_exit routine Benjamin Thery
2008-06-18 20:19   ` Eric W. Biederman
2008-06-23  2:16   ` Tejun Heo
2008-06-18 17:09 ` [PATCH 10/11] netns: Enable tagging for net_class directories in sysfs Benjamin Thery
2008-06-23  2:18   ` Tejun Heo
2008-06-18 17:09 ` [PATCH 11/11] sysfs: user namespaces: fix bug with clone(CLONE_NEWUSER) with fairsched Benjamin Thery
2008-06-23  2:18   ` Tejun Heo
2008-06-25 18:44     ` Serge E. Hallyn
2008-06-25 21:11       ` Eric W. Biederman
2008-06-26 13:07         ` Serge E. Hallyn
  -- strict thread matches above, loose matches on Subject: below --
2008-06-06 15:46 [PATCH 00/11] sysfs tagged directories V5 Benjamin Thery
2008-06-06 15:47 ` [PATCH 01/11] sysfs: Support for preventing unmounts Benjamin Thery
2008-05-06 17:30 [RESEND][PATCH 00/11] sysfs tagged directories Benjamin Thery
2008-05-06 17:30 ` [PATCH 01/11] sysfs: Support for preventing unmounts Benjamin Thery

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