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From: Ian Kent <raven@themaw.net>
To: Miklos Szeredi <miklos@szeredi.hu>, David Howells <dhowells@redhat.com>
Cc: viro@zeniv.linux.org.uk, torvalds@linux-foundation.org,
	mszeredi@redhat.com, christian@brauner.io, jannh@google.com,
	darrick.wong@oracle.com, kzak@redhat.com, jlayton@redhat.com,
	linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 10/18] fsinfo: Provide notification overrun handling support [ver #21]
Date: Wed, 05 Aug 2020 10:46:02 +0800	[thread overview]
Message-ID: <5078554c6028e29c91d815c63e2af1ffac2ecbbb.camel@themaw.net> (raw)
In-Reply-To: <94bba6f200bb2bbf83f4945faa2ccb83fd947540.camel@themaw.net>

On Wed, 2020-08-05 at 10:05 +0800, Ian Kent wrote:
> On Tue, 2020-08-04 at 15:56 +0200, Miklos Szeredi wrote:
> > On Mon, Aug 03, 2020 at 02:37:50PM +0100, David Howells wrote:
> > > Provide support for the handling of an overrun in a watch
> > > queue.  In the
> > > event that an overrun occurs, the watcher needs to be able to
> > > find
> > > out what
> > > it was that they missed.  To this end, previous patches added
> > > event
> > > counters to struct mount.
> > 
> > So this is optimizing the buffer overrun case?
> > 
> > Shoun't we just make sure that the likelyhood of overruns is low
> > and
> > if it
> > happens, just reinitialize everthing from scratch (shouldn't be
> > *that*
> > expensive).
> 
> But maybe not possible if you are using notifications for tracking
> state in user space, you need to know when the thing you have needs
> to be synced because you missed something and it's during the
> notification processing you actually have the object that may need
> to be refreshed.
> 
> > Trying to find out what was missed seems like just adding
> > complexity
> > for no good
> > reason.

Coming back to an actual use case.

What I said above is one aspect but, since I'm looking at this right
now with systemd, and I do have the legacy code to fall back to, the
"just reset everything" suggestion does make sense.

But I'm struggling to see how I can identify notification buffer
overrun in libmount, and overrun is just one possibility for lost
notifications, so I like the idea that, as a library user, I can
work out that I need to take action based on what I have in the
notifications themselves.

Ian


  reply	other threads:[~2020-08-05  2:46 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-03 13:36 [PATCH 00/18] VFS: Filesystem information " David Howells
2020-08-03 13:36 ` [PATCH 01/18] fsinfo: Introduce a non-repeating system-unique superblock ID " David Howells
2020-08-04  9:34   ` Miklos Szeredi
2020-08-03 13:36 ` [PATCH 02/18] fsinfo: Add fsinfo() syscall to query filesystem information " David Howells
2020-08-04 10:16   ` Miklos Szeredi
2020-08-04 11:34   ` David Howells
2020-08-27 11:27   ` Michael Kerrisk (man-pages)
2020-08-03 13:36 ` [PATCH 03/18] fsinfo: Provide a bitmap of the features a filesystem supports " David Howells
2020-08-03 13:37 ` [PATCH 04/18] fsinfo: Allow retrieval of superblock devname, options and stats " David Howells
2020-08-03 13:37 ` [PATCH 05/18] fsinfo: Allow fsinfo() to look up a mount object by ID " David Howells
2020-08-04 10:33   ` Miklos Szeredi
2020-08-03 13:37 ` [PATCH 06/18] fsinfo: Add a uniquifier ID to struct mount " David Howells
2020-08-04 10:41   ` Miklos Szeredi
2020-08-04 12:32     ` Ian Kent
2020-08-05 14:13   ` David Howells
2020-08-05 14:46     ` Miklos Szeredi
2020-08-05 15:30     ` David Howells
2020-08-05 19:33       ` Matthew Wilcox
2020-08-06  5:43         ` Ian Kent
2020-08-03 13:37 ` [PATCH 07/18] fsinfo: Allow mount information to be queried " David Howells
2020-08-03 13:37 ` [PATCH 08/18] fsinfo: Allow mount topology and propagation info to be retrieved " David Howells
2020-08-04 13:38   ` Miklos Szeredi
2020-08-05 15:37   ` David Howells
2020-08-05 17:19     ` Miklos Szeredi
2020-08-03 13:37 ` [PATCH 09/18] watch_queue: Mount event counters " David Howells
2020-08-03 13:37 ` [PATCH 10/18] fsinfo: Provide notification overrun handling support " David Howells
2020-08-04 13:56   ` Miklos Szeredi
2020-08-05  2:05     ` Ian Kent
2020-08-05  2:46       ` Ian Kent [this message]
2020-08-05  7:45         ` Miklos Szeredi
2020-08-05 11:23           ` Ian Kent
2020-08-05 11:27             ` Miklos Szeredi
2020-08-06  1:47               ` Ian Kent
2020-08-05 16:06   ` David Howells
2020-08-05 17:26     ` Miklos Szeredi
2020-08-03 13:37 ` [PATCH 11/18] fsinfo: sample: Mount listing program " David Howells
2020-08-03 13:38 ` [PATCH 12/18] fsinfo: Add API documentation " David Howells
2020-08-03 13:38 ` [PATCH 13/18] fsinfo: Add support for AFS " David Howells
2020-08-03 13:38 ` [PATCH 14/18] fsinfo: Add support to ext4 " David Howells
2020-08-03 13:38 ` [PATCH 15/18] fsinfo: Add an attribute that lists all the visible mounts in a namespace " David Howells
2020-08-04 14:05   ` Miklos Szeredi
2020-08-05  0:59     ` Ian Kent
2020-08-05 16:44   ` David Howells
2020-08-03 13:38 ` [PATCH 16/18] errseq: add a new errseq_scrape function " David Howells
2020-08-03 13:38 ` [PATCH 17/18] vfs: allow fsinfo to fetch the current state of s_wb_err " David Howells
2020-08-03 13:39 ` [PATCH 18/18] samples: add error state information to test-fsinfo.c " David Howells
2020-08-04 15:39 ` [PATCH 00/18] VFS: Filesystem information " James Bottomley
2020-08-04 19:18   ` Miklos Szeredi
2020-08-05 17:13 ` David Howells

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