Messages in this thread | | | Date | Tue, 29 Apr 2008 18:11:07 -0400 | Subject | Re: [LTP/VFS] fcntl SETLEASE fails on ramfs/tmpfs | From | "J. Bruce Fields" <> |
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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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