Hi Zach, On Fri, Apr 10, 2015 at 6:00 PM, Zach Brown <zab@xxxxxxxxxx> wrote: > Add a copy_file_range() system call for offloading copies between > regular files. > > This gives an interface to underlying layers of the storage stack which > can copy without reading and writing all the data. There are a few > candidates that should support copy offloading in the nearer term: > > - btrfs shares extent references with its clone ioctl > - NFS has patches to add a COPY command which copies on the server > - SCSI has a family of XCOPY commands which copy in the device > > This system call avoids the complexity of also accelerating the creation > of the destination file by operating on an existing destination file > descriptor, not a path. > > Currently the high level vfs entry point limits copy offloading to files > on the same mount and super (and not in the same file). This can be > relaxed if we get implementations which can copy between file systems > safely. > > Signed-off-by: Zach Brown <zab@xxxxxxxxxx> > --- > fs/read_write.c | 129 ++++++++++++++++++++++++++++++++++++++ > include/linux/fs.h | 3 + > include/uapi/asm-generic/unistd.h | 4 +- > kernel/sys_ni.c | 1 + > 4 files changed, 136 insertions(+), 1 deletion(-) > > diff --git a/fs/read_write.c b/fs/read_write.c > index 8e1b687..c65ce1d 100644 > --- a/fs/read_write.c > +++ b/fs/read_write.c > @@ -17,6 +17,7 @@ > #include <linux/pagemap.h> > #include <linux/splice.h> > #include <linux/compat.h> > +#include <linux/mount.h> > #include "internal.h" > > #include <asm/uaccess.h> > @@ -1424,3 +1425,131 @@ COMPAT_SYSCALL_DEFINE4(sendfile64, int, out_fd, int, in_fd, > return do_sendfile(out_fd, in_fd, NULL, count, 0); > } > #endif > + > +/* > + * copy_file_range() differs from regular file read and write in that it > + * specifically allows return partial success. When it does so is up to > + * the copy_file_range method. > + */ > +ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in, > + struct file *file_out, loff_t pos_out, > + size_t len, int flags) I'm going to repeat a gripe with this interface. I really don't think we should treat copy_file_range() as taking a size_t length, since that is not sufficient to do a full file copy on 32-bit systems w/ LFS support. Could we perhaps instead of a length, define a 'pos_in_start' and a 'pos_in_end' offset (with the latter being -1 for a full-file copy) and then return an 'loff_t' value stating where the copy ended? Note that both btrfs and NFSv4.2 allow for 64-bit lengths, so this interface would be closer to what is already in use anyway. Cheers Trond -- 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
