On Wed, Oct 14, 2015 at 10:59 AM, Anna Schumaker <Anna.Schumaker@xxxxxxxxxx> wrote: > On 10/12/2015 07:17 PM, Darrick J. Wong wrote: >> 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. > > So what I'm hearing is that I should drop the reflink and dedup flags and change this system call only perform a full copy (with preserving of sparseness), correct? I can make those changes, but only if everybody is in agreement that it's the best way forward. I personally rather like the reflink option. That thing is quite useful. > > The only reason I haven't done anything to make this system call interruptible is because I haven't been able to find any documentation or examples for making system calls interruptible. How do I do this? > For just interruptability, avoid waiting in non-interruptable ways and return -EINTR if one of your wait calls returns -EINTR. For restartability, it's more complicated. There are special values you can return that give the signal code hints as to what to do. --Andy -- 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
