* Matthew Wilcox: > On Sun, Aug 15, 2010 at 05:06:58PM +0200, Florian Weimer wrote: >> It seems that it might be useful to have a locally shared, globally >> exclusive file lock. "Local" is defined as "when the file is mapped >> shared, memory accesses follow the architecture memory model across >> threads and processes, and shared POSIX mutexes work". This could be >> used to make the new WAL code in SQLite 3.7 more foolproof, but there >> are other applications which would benefit as well. > > This sounds like you're trying to fix a problem with NFS. I think there > are network filesystems which practice mmap coherency. In the sense that I described? This surprises me. (I know that there is something called Distributed Shared Memory. But it's generally got different properties than a mapped file, AFAIK.) >> It seems to me that this would not need changes to network file >> systems because you can implement it by acquring a traditional >> fcntl()-style exclusive lock on the network side, without creating a >> corresponding local lock. > > fcntl locks are advisory ... That's not a problem for this use case. It's about making sure that an SQLite-using application cannot accidentally access the same database without proper locking because the mutexes are not visible across a network file system. -- 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
