On Sun, Oct 11, 2015 at 07:22:03AM -0700, Christoph Hellwig wrote: > On Wed, Sep 30, 2015 at 01:26:52PM -0400, Anna Schumaker wrote: > > This allows us to have an in-kernel copy mechanism that avoids frequent > > switches between kernel and user space. This is especially useful so > > NFSD can support server-side copies. > > > > I make pagecache copies configurable by adding three new (exclusive) > > flags: > > - COPY_FR_REFLINK tells vfs_copy_file_range() to only create a reflink. > > - COPY_FR_COPY does a full data copy, but may be filesystem accelerated. > > - COPY_FR_DEDUP creates a reflink, but only if the contents of both > > ranges are identical. > > All but FR_COPY really should be a separate system call. Clones (an > dedup as a special case of clones) are really a separate beast from file > copies. > > If I want to clone a file I either want it clone fully or fail, not copy > a certain amount. That means that a) we need to return an error not > short "write", and b) locking impementations are important - we need to > prevent other applications from racing with our clone even if it is > large, while to get these semantics for the possible short returning > file copy will require a proper userland locking protocol. Last but not > least file copies need to be interruptible while clones should be not. > All this is already important for local file systems and even more > important for NFS exporting. > > So I'd suggest to drop this patch and just let your syscall handle > actualy copies with all their horrors. We can go with Peng's patches > to generalize the btrfs ioctls for clones for now which is what everyone > already uses anyway, and then add a separate sys_file_clone later. Hm. Peng's patches only generalize the CLONE and CLONE_RANGE ioctls from btrfs, however they don't port over the (vastly different) EXTENT_SAME ioctl. What does everyone think about generalizing EXTENT_SAME? The interface enables one to ask the kernel to dedupe multiple file ranges in a single call. That's more complex than what I was proposing with COPY_FR_DEDUP(E), but I'm assuming that the extra complexity buys us the ability to ... multi-dedupe at the same time, with locks held on the source file? I'm happy to generalize the existing EXTENT_SAME, but please yell if you really hate the interface. --D > -- > To unsubscribe from this list: send the line "unsubscribe linux-api" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
