[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. Anyway, returning to your point about flock(), how would this text look for the flock(2) manual page: NOTES Since kernel 2.0, flock() is implemented as a system call in its own right rather than being emulated in the GNU C library as a call to fcntl(2). This yields classical BSD semantics: there is no interaction between the types of lock placed by flock() and fcntl(2), and flock() does not detect deadlock. (Note, however, that on some modern BSDs, flock() and fcntl(2) locks do interact with one another.) In Linux kernels up to 2.6.11, flock() does not lock files over NFS (i.e., the scope of locks was limited to the local system). Instead, one could use fcntl(2) byte-range locking, which does work over NFS, given a sufficiently recent version of Linux and a server which supports locking. Since Linux 2.6.12, NFS clients support flock() locks by emulating them as byte-range locks on the entire file. This means that fcntl(2) and flock() locks do interact with one another over NFS. Since Linux 2.6.37, the kernel supports a compatibility mode that allows flock() locks (and also fcntl(2) byte region locks) to be treated as local; see the discussion of the local_lock option in nfs(5). ? Thanks, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
