linux-kernel - Re: [LTP/VFS] fcntl SETLEASE fails on ramfs/tmpfs

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Date:	Tue, 29 Apr 2008 18:15:01 -0400
From:	"Mike Frysinger" <vapier.adi@...il.com>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Bryan Wu" <cooloney@...nel.org>, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, willy@...ian.org,
	viro@...iv.linux.org.uk, uclinux-dist-devel@...ckfin.uclinux.org,
	richterd@...i.umich.edu
Subject: Re: [LTP/VFS] fcntl SETLEASE fails on ramfs/tmpfs

On Tue, Apr 29, 2008 at 6:11 PM, J. Bruce Fields <bfields@...ldses.org> wrote:
> On Tue, Apr 29, 2008 at 06:01:47PM -0400, Mike Frysinger wrote:
>  > On Tue, Apr 29, 2008 at 5:42 PM, J. Bruce Fields <bfields@...ldses.org> wrote:
>  > >  The one thing I suspect is *not* a really serious problem here is the
>  > >  reported LTP failure, since probably the only user of this is Samba,
>  > >  which probably doesn't do a lot of tmpfs exports, and in any case it can
>  > >  probably soldier on (if with degraded performance--how badly I don't
>  > >  know) without getting the write lease it wants.
>  >
>  > i'm not sure i follow.  the reported problem is that file locking does
>  > not work on tmpfs/ramfs storage.  a not terribly uncommon scenario is
>  > to use tmpfs on /tmp (or similar location) and have file locking not
>  > work at all.  so programs that use file locking or scripts that
>  > leverage the flock utility from the util-linux package break.
>
>  There are three different mechanisms that might be called "file locks":
>
>         - fcntl() locks, aka "posix locks", "byte-range locks":
>           documented in the "Advisory locking" section of fcntl(2).
>         - flock() locks: documented in flock(2) This is what the shell
>           utility from util-linux uses.
>         - leases, documented in the "Leases" section of fcntl(2).
>
>  For the former two, I agree with you, applications actually depend on
>  them.
>
>  The bug report, however, is for leases, which are much less widely used.
>  (The only users I know of are Samba and, to a lesser extent, NFSv4
>  (which doesn't currently use write leases due to all these problems).)

ah sorry, you're right of course ... while i investigated the issue
originally, i clearly forget the details ;)
-mike
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