On Wed, May 16, 2012 at 9:02 AM, Matthew Wilcox <willy@xxxxxxxxxxxxxxx> wrote: > On Tue, May 15, 2012 at 04:02:01PM -0700, Andy Lutomirski wrote: >> I would love to use this from userspace. If I could carve out a little >> piece of NVM as a file (or whatever) and mmap it, I could do all kinds >> of fun things with that. It would be nice if it had well-defined, or at >> least configurable or discoverable, caching properties (e.g. WB, WT, WC, >> UC, etc.). > > Yes, usage from userspace is definitely planned; again through a > filesystem interface. Treating it like a regular file will work as > expected; the question is how to expose the interesting properties > (eg is there a lighter weight mechanism than calling msync()). clfush? vdso system call? If there's a proliferation of different technologies like this, we could have an opaque struct nvm_mapping and a vdso call like void __vdso_nvm_flush_writes(struct nvm_mapping *mapping, void *address, size_t len); that would read the struct nvm_mapping to figure out whether it should do a clflush, sfence, mfence, posting read, or whatever else the particular device needs. (This would also give a much better chance of portability to architectures other than x86.) > > My hope was that by having a discussion of how to use this stuff within > the kernel, we might come up with some usage models that would inform > how we design a user space library. > >> (Even better would be a way to make a clone of an fd that only allows >> mmap, but that's a mostly unrelated issue.) > > O_MMAP_ONLY? And I'm not sure why you'd want to forbid reads and writes. I don't want to forbid reads and writes; I want to forbid ftruncate. That way I don't need to worry about malicious / obnoxious programs sharing the fd causing SIGBUS. --Andy -- 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
