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From: David Howells <dhowells@redhat.com>
To: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Cc: dhowells@redhat.com, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH 0/4] Enhanced file stat system call
Date: Thu, 17 Nov 2016 16:45:45 +0000	[thread overview]
Message-ID: <15516.1479401145@warthog.procyon.org.uk> (raw)
In-Reply-To: <20161117143904.4ae757b4@lxorguk.ukuu.org.uk>

One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> wrote:

> >  (2) Lightweight stat (AT_STATX_DONT_SYNC): Ask for just those details of
> >      interest, and allow a network fs to approximate anything not of
> >      interest, without going to the server.
> > 
> >  (3) Heavyweight stat (AT_STATX_FORCE_SYNC): Force a network fs to flush
> >      buffers and go to the server, even if it thinks its cached attributes
> >      are up to date.
> 
> That seems an odd way to do it. Wouldn't it be cleaner and more flexible
> to give a timestamp of the oldest time you consider acceptable (and
> obviously passing 0 indicates whatever you have)

Perhaps, though adding 6-argument syscalls is apparently frowned upon.

> > Note that no lstat() equivalent is required as that can be implemented
> > through statx() with atflag == 0.  There is also no fstat() equivalent as
> > that can be implemented through statx() with filename == NULL and the
> > relevant fd passed as dfd.
> 
> and dfd + a name gives you fstatat() ?

Yes.

> The cover note could be clearer on this.

Fixed.

> Should the fields really be split the way they are for times rather than
> a struct for each one so you can write code generically to handle one of
> those rather than having to have a 4 way switch statement all the time.

It depends.  Doing so leaves 16 bytes of hole in the structure.  I could
ameliorate the wastage by using a union to overlay useful fields in the gaps,
but that's pretty icky and might be compiler dependent.

> Another attribute that would be nice (but migt need some trivial device
> layer tweaking) would be STATX_ATTR_VOLATILE for filesystems that will
> probably evaporate on a reboot. That's useful information for tools like
> installers and also for sanity checking things like backup paths.

There's a FILE_ATTRIBUTE_TEMPORARY that I could map for windows filesystems
that could be used with this.

> Remote needs to have clear semantics: is ext4fs over nbd 'remote' for
> example ?

Hmmm... Interesting question.  Probably should.  But you could be insane and
RAID an nbd and a local disk.  Further, does NFS over a loopback device to
nfsd on the same machine qualify as root?  What if that's exposing a local fs
on NBD?  Perhaps I should drop 'REMOTE' for now.  It sounds like something
that a GUI filemanager might find interesting, though.

David

  parent reply	other threads:[~2016-11-17 17:03 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-11-17 13:34 David Howells
2016-11-17 13:35 ` [PATCH 1/4] statx: Add a system call to make enhanced file info available David Howells
2016-11-17 18:39   ` Jeff Layton
2016-11-18  2:32     ` Andreas Dilger
2016-11-18  8:59     ` David Howells
2016-11-18  8:59       ` David Howells
2016-11-18  9:25       ` Andreas Dilger
2016-11-18  9:25         ` Andreas Dilger
2016-11-17 23:40   ` Dave Chinner
2016-11-18  3:28     ` Andreas Dilger
2016-11-18 22:07       ` Dave Chinner
2016-11-18 22:54       ` David Howells
2016-11-19 22:43         ` Dave Chinner
2016-11-21 14:30         ` One Thousand Gnomes
2016-11-21 20:43           ` Dave Chinner
2016-11-22 10:39         ` David Howells
2016-11-22 13:55           ` Jeff Layton
2016-11-22 20:58           ` Dave Chinner
2016-11-18  9:53     ` David Howells
2016-11-18  8:48   ` David Howells
2016-11-18 12:01     ` Jeff Layton
2016-11-18  9:36   ` David Howells
2016-11-18 17:17     ` Jeff Layton
2016-11-18 18:04     ` David Howells
2016-11-18 18:54       ` Jeff Layton
2016-11-18 19:08       ` David Howells
2016-11-18  9:43   ` David Howells
2016-11-18 21:41     ` Dave Chinner
2016-11-18 22:24     ` David Howells
2016-11-18 10:29   ` David Howells
2016-11-18 10:29     ` David Howells
2016-11-18 21:27     ` Dave Chinner
2016-11-18 21:48     ` David Howells
2016-11-18 21:48       ` David Howells
2016-11-18 22:17       ` Dave Chinner
2016-11-18 22:17         ` Dave Chinner
2016-11-19 10:21         ` Michael Kerrisk (man-pages)
2016-11-17 13:35 ` [PATCH 2/4] statx: Ext4: Return enhanced file attributes David Howells
2016-11-18  3:30   ` Andreas Dilger
2016-11-17 13:35 ` [PATCH 3/4] statx: NFS: " David Howells
2016-11-17 13:35 ` [PATCH 4/4] statx: AFS: " David Howells
2016-11-18  3:34   ` Andreas Dilger
2016-11-18  8:47   ` David Howells
2016-11-17 14:39 ` [RFC][PATCH 0/4] Enhanced file stat system call One Thousand Gnomes
2016-11-17 15:10 ` Michael Kerrisk
2016-11-17 16:33 ` David Howells
2016-11-17 16:45 ` David Howells [this message]
2016-11-17 20:00   ` J. Bruce Fields
2016-11-18  2:30     ` Andreas Dilger
2016-11-18  4:29       ` NeilBrown
2016-11-18 13:41   ` One Thousand Gnomes
2016-11-18 13:49   ` David Howells

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