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SubjectRe: [LTP/VFS] fcntl SETLEASE fails on ramfs/tmpfs
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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@fieldses.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).)

--b.


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