On Sun, 27 Apr 2014 13:11:33 +0200 "Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx> wrote: > On Sun, Apr 27, 2014 at 12:04 PM, NeilBrown <neilb@xxxxxxx> wrote: > > On Sun, 27 Apr 2014 11:16:02 +0200 "Michael Kerrisk (man-pages)" > > <mtk.manpages@xxxxxxxxx> wrote: > > > >> [Trimming some folk from CC, and adding various NFS people] > >> > >> On 04/27/2014 06:51 AM, NeilBrown wrote: > >> > >> [...] > >> > >> > Note to Michael: The text > >> > flock() does not lock files over NFS. > >> > in flock(2) is no longer accurate. The reality is ... complex. > >> > See nfs(5), and search for "local_lock". > >> > >> Ahhh -- I see: > >> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=5eebde23223aeb0ad2d9e3be6590ff8bbfab0fc2 > >> > >> Thanks for the heads up. > >> > >> Just in general, it would be great if the flock(2) and fcntl(2) man pages > >> contained correct details for NFS, of course. So, for example, if there > >> are any current gotchas for NFS and fcntl() byte-range locking, I'd like > >> to add those to the fcntl(2) man page. > > > > The only peculiarities I can think of are: > > - With NFS, locking or unlocking a region forces a flush of any cached data > > for that file (or maybe for the region of the file). I'm not sure if this > > is worth mentioning. > > I agree that it's probably not necessary to mention. > > > - With NFSv4 the client can lose a lock if it is out of contact with the > > server for a period of time. When this happens, any IO to the file by a > > process which "thinks" it holds a lock will fail until that process closes > > and re-opens the file. > > This behaviour is since 3.12. Prior to that the client might lose and > > regain the lock without ever knowing thus potentially risking corruption > > (but only if client and server lost contact for an extended period). > > Do you have a pointer for that commit to 3.12? > http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=ef1820f9be27b6ad158f433ab38002ab8131db4d did most of the work while the subsequent commit http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=f6de7a39c181dfb8a2c534661a53c73afb3081cd changed some details, added some documentation, and inverted the default behaviour. NeilBrown
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