From: "J. Bruce Fields" <bfields@fieldses.org>
To: Pavel Emelyanov <xemul@parallels.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
Cyrill Gorcunov <gorcunov@openvz.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Alexey Dobriyan <adobriyan@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
James Bottomley <jbottomley@parallels.com>,
Matthew Helsley <matt.helsley@gmail.com>
Subject: Re: [patch 4/8] fs, exportfs: Add export_encode_inode_fh helper
Date: Tue, 21 Aug 2012 08:09:09 -0400 [thread overview]
Message-ID: <20120821120908.GB9483@fieldses.org> (raw)
In-Reply-To: <503367CB.9080609@parallels.com>
On Tue, Aug 21, 2012 at 02:49:47PM +0400, Pavel Emelyanov wrote:
> On 08/21/2012 02:42 PM, Aneesh Kumar K.V wrote:
> > Pavel Emelyanov <xemul@parallels.com> writes:
> >
> >> On 08/20/2012 11:32 PM, J. Bruce Fields wrote:
> >>> On Mon, Aug 20, 2012 at 11:06:06PM +0400, Cyrill Gorcunov wrote:
> >>>> On Mon, Aug 20, 2012 at 02:32:25PM -0400, J. Bruce Fields wrote:
> >>>>> On Mon, Aug 20, 2012 at 08:33:38PM +0400, Cyrill Gorcunov wrote:
> >>>>>> On Mon, Aug 20, 2012 at 07:49:23PM +0530, Aneesh Kumar K.V wrote:
> >>>>>>> Cyrill Gorcunov <gorcunov@openvz.org> writes:
> >>>>>>>
> >>>>>>>> To provide fsnotify object inodes being watched without
> >>>>>>>> binding to alphabetical path we need to encode them with
> >>>>>>>> exportfs help. This patch adds a helper which operates
> >>>>>>>> with plain inodes directly.
> >>>>>>>
> >>>>>>> doesn't name_to_handle_at() work for you ? It also allows to get a file
> >>>>>>> handle using file descriptor.
> >>>>>>
> >>>>>> Hi, sorry for dealy. Well, the last idea is to get rid of this helper,
> >>>>>> I've sent out an updated version where ino+dev is only printed.
> >>>>>
> >>>>> I don't understand how ino and dev are useful to you, though, if you're
> >>>>> still hoping to be able to look up inodes using this information later
> >>>>> on.
> >>>>
> >>>> Hi Bruce, I believe having ino+dev is better than nothing. Otherwise we
> >>>> simply have no clue which targets are bound to inotify mark. Sometime
> >>>> (!) we can try to generate fhandle in userspace from this ino+dev bundle
> >>>> and then open the target file.
> >>>
> >>> That's insufficient to generate a filehandle in general.
> >>
> >> Yes, sure, but for live migration having inode and device is enough and that's why.
> >> We can use two ways of having a filesystem on the target machine in the same
> >> state (from paths points of view) as it was on destination one:
> >>
> >> 1. copy file tree in a rsync manner
> >> 2. copy a virtual disk image file
> >>
> >> In the 1st case we can map inode number to path easily, since we iterate over a filesystem
OK. Then you don't care about unlinked files?
If the filesystem's frozen by the time you get here, I suppose you could
also just use paths?
> >> anyway. I agree, that rsync is not perfect for migration but still.
> >>
> >> In the 2nd case we can generate filehandle out of an inode number only since we _do_ know
> >> that inode will not get reused.
> >
> > If you are going to to use open_by_handle, then that handle is not
> > sufficient right ? Or do you have open_by_inode ? as part of c/r ?
>
> Why? For e.g. ext4 you can construct a handle in userspace and open by it.
If it's a real filehandle you want, in general you don't want to
construct it in userspace--depending on the filesystem it may require
filesystem-specific knowledge.
--b.
>
> >>
> >> However, if you have some better ideas on what information about inode should be exported
> >> to the userspace please share.
> >>
> >
> > Why not use name_to_handle(fd,...) and open_by_handle(handle,..) ?
>
> Because we don't have an fd at hands by the time we need to know the handle.
>
> >
> >>> (Also: there's the usual inode-number aliasing problem: the inode number
> >>> could get reused by another file. Unless you know the file is being
> >>> held open the whole time.)
> >>>
> >
> > -aneesh
> >
> > .
> >
>
> Thanks,
> Pavel
next prev parent reply other threads:[~2012-08-21 12:09 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-15 9:21 [patch 0/8] procfs, fdinfo updated Cyrill Gorcunov
2012-08-15 9:21 ` [patch 1/8] procfs: Move /proc/pid/fd[info] handling code to fd.[ch] Cyrill Gorcunov
2012-08-15 9:21 ` [patch 2/8] procfs: Convert /proc/pid/fdinfo/ handling routines to seq-file Cyrill Gorcunov
2012-08-15 9:21 ` [patch 3/8] procfs: Add ability to plug in auxiliary fdinfo providers Cyrill Gorcunov
2012-08-15 21:16 ` Al Viro
2012-08-15 21:31 ` Cyrill Gorcunov
2012-08-15 21:29 ` Al Viro
2012-08-15 21:34 ` Cyrill Gorcunov
2012-08-16 10:58 ` Cyrill Gorcunov
2012-08-15 9:21 ` [patch 4/8] fs, exportfs: Add export_encode_inode_fh helper Cyrill Gorcunov
2012-08-15 20:45 ` J. Bruce Fields
2012-08-15 21:02 ` Cyrill Gorcunov
2012-08-15 22:06 ` J. Bruce Fields
2012-08-16 6:24 ` Cyrill Gorcunov
2012-08-16 12:38 ` Cyrill Gorcunov
2012-08-16 12:47 ` J. Bruce Fields
2012-08-16 13:16 ` Cyrill Gorcunov
2012-08-16 14:57 ` Cyrill Gorcunov
2012-08-16 15:05 ` Al Viro
2012-08-16 15:09 ` Cyrill Gorcunov
2012-08-16 13:43 ` Al Viro
2012-08-16 13:47 ` Pavel Emelyanov
2012-08-16 13:50 ` Al Viro
2012-08-16 13:53 ` Pavel Emelyanov
2012-08-16 13:54 ` Cyrill Gorcunov
2012-08-16 14:03 ` James Bottomley
2012-08-16 14:13 ` Pavel Emelyanov
2012-08-16 14:15 ` Cyrill Gorcunov
2012-08-16 14:41 ` Al Viro
2012-08-16 14:48 ` Cyrill Gorcunov
2012-08-16 14:54 ` J. Bruce Fields
2012-08-16 14:55 ` Al Viro
2012-08-16 15:06 ` Pavel Emelyanov
2012-08-16 15:35 ` Cyrill Gorcunov
2012-08-16 15:07 ` Cyrill Gorcunov
2012-08-17 20:58 ` Eric W. Biederman
2012-08-16 13:48 ` Al Viro
2012-08-20 14:19 ` Aneesh Kumar K.V
2012-08-20 16:33 ` Cyrill Gorcunov
2012-08-20 18:32 ` J. Bruce Fields
2012-08-20 19:06 ` Cyrill Gorcunov
2012-08-20 19:32 ` J. Bruce Fields
2012-08-20 19:40 ` Cyrill Gorcunov
2012-08-21 9:18 ` Pavel Emelyanov
2012-08-21 10:42 ` Aneesh Kumar K.V
2012-08-21 10:49 ` Pavel Emelyanov
2012-08-21 10:54 ` Cyrill Gorcunov
2012-08-21 11:09 ` Pavel Emelyanov
2012-08-21 12:11 ` J. Bruce Fields
2012-08-21 12:22 ` Pavel Emelyanov
2012-08-21 12:29 ` J. Bruce Fields
2012-08-21 12:40 ` Pavel Emelyanov
2012-08-21 12:51 ` Boaz Harrosh
2012-08-21 12:59 ` Pavel Emelyanov
2012-08-21 13:08 ` Boaz Harrosh
2012-08-21 13:12 ` Al Viro
2012-08-21 13:40 ` Cyrill Gorcunov
2012-08-21 12:09 ` J. Bruce Fields [this message]
2012-08-21 12:25 ` Pavel Emelyanov
2012-08-22 5:49 ` Aneesh Kumar K.V
2012-08-23 8:06 ` Cyrill Gorcunov
2012-08-23 8:54 ` Marco Stornelli
2012-08-23 9:29 ` Cyrill Gorcunov
2012-08-15 9:21 ` [patch 5/8] fs, notify: Add procfs fdinfo helper v3 Cyrill Gorcunov
2012-08-15 9:21 ` [patch 6/8] fs, eventfd: Add procfs fdinfo helper Cyrill Gorcunov
2012-08-15 9:21 ` [patch 7/8] fs, epoll: Add procfs fdinfo helper v2 Cyrill Gorcunov
2012-08-15 9:21 ` [patch 8/8] fdinfo: Show sigmask for signalfd fd v2 Cyrill Gorcunov
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