+/*
+ * Map an iov into an array of pages and offset/length tupples. With the
+ * partial_page structure, we can map several non-contiguous ranges into
+ * our ones pages[] map instead of splitting that operation into pieces.
+ * Could easily be exported as a generic helper for other users, in which
+ * case one would probably want to add a 'max_nr_pages' parameter as well.
+ */
+static int get_iovec_page_array(const struct iovec __user *iov,
+ unsigned int nr_vecs, struct page **pages,
+ struct partial_page *partial, int aligned)
+{
+ int buffers = 0, error = 0;
+
+ /*
+ * It's ok to take the mmap_sem for reading, even
+ * across a "get_user()".
+ */
+ down_read(¤t->mm->mmap_sem);
+
+ while (nr_vecs) {
+ unsigned long off, npages;
+ void __user *base;
+ size_t len;
+ int i;
+
+ /*
+ * Get user address base and length for this iovec.
+ */
+ error = get_user(base, &iov->iov_base);
+ if (unlikely(error))
+ break;
+ error = get_user(len, &iov->iov_len);
+ if (unlikely(error))
+ break;
+
+ /*
+ * Sanity check this iovec. 0 read succeeds.
+ */
+ if (unlikely(!len))
+ break;
+ error = -EFAULT;
+ if (unlikely(!base))
+ break;
+
+ /*
+ * Get this base offset and number of pages, then map
+ * in the user pages.
+ */
+ off = (unsigned long) base & ~PAGE_MASK;
+
+ /*
+ * If asked for alignment, the offset must be zero and the
+ * length a multiple of the PAGE_SIZE.
+ */
+ error = -EINVAL;
+ if (aligned && (off || len & ~PAGE_MASK))
+ break;
+
+ npages = (off + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
+ if (npages > PIPE_BUFFERS - buffers)
+ npages = PIPE_BUFFERS - buffers;
+
+ error = get_user_pages(current, current->mm,
+ (unsigned long) base, npages, 0, 0,
+ &pages[buffers], NULL);
+
+ if (unlikely(error <= 0))
+ break;
+
+ /*
+ * Fill this contiguous range into the partial page map.
+ */
+ for (i = 0; i < error; i++) {
+ const int plen = min_t(size_t, len, PAGE_SIZE - off);
+
+ partial[buffers].offset = off;
+ partial[buffers].len = plen;
+
+ off = 0;
+ len -= plen;
+ buffers++;
+ }
+
+ /*
+ * We didn't complete this iov, stop here since it probably
+ * means we have to move some of this into a pipe to
+ * be able to continue.
+ */
+ if (len)
+ break;
+
+ /*
+ * Don't continue if we mapped fewer pages than we asked for,
+ * or if we mapped the max number of pages that we have
+ * room for.
+ */
+ if (error < npages || buffers == PIPE_BUFFERS)
+ break;
+
+ nr_vecs--;
+ iov++;
+ }
+
+ up_read(¤t->mm->mmap_sem);
+
+ if (buffers)
+ return buffers;
+
+ return error;
+}
+
+/*
+ * vmsplice splices a user address range into a pipe. It can be thought of
+ * as splice-from-memory, where the regular splice is splice-from-file (or
+ * to file). In both cases the output is a pipe, naturally.
+ *
+ * Note that vmsplice only supports splicing _from_ user memory to a pipe,
+ * not the other way around. Splicing from user memory is a simple operation
+ * that can be supported without any funky alignment restrictions or nasty
+ * vm tricks. We simply map in the user memory and fill them into a pipe.
+ * The reverse isn't quite as easy, though. There are two possible solutions
+ * for that:
+ *
+ * - memcpy() the data internally, at which point we might as well just
+ * do a regular read() on the buffer anyway.
+ * - Lots of nasty vm tricks, that are neither fast nor flexible (it
+ * has restriction limitations on both ends of the pipe).
+ *
+ * Alas, it isn't here.
+ *
+ */
+static long do_vmsplice(struct file *file, const struct iovec __user *iov,
+ unsigned long nr_segs, unsigned int flags)
+{
+ struct pipe_inode_info *pipe = file->f_dentry->d_inode->i_pipe;
+ struct page *pages[PIPE_BUFFERS];
+ struct partial_page partial[PIPE_BUFFERS];
+ struct splice_pipe_desc spd = {
+ .pages = pages,
+ .partial = partial,
+ .flags = flags,
+ .ops = &user_page_pipe_buf_ops,
+ };
+
+ if (unlikely(!pipe))
+ return -EBADF;
+ if (unlikely(nr_segs > UIO_MAXIOV))
+ return -EINVAL;
+ else if (unlikely(!nr_segs))
+ return 0;
+
+ spd.nr_pages = get_iovec_page_array(iov, nr_segs, pages, partial,
+ flags & SPLICE_F_GIFT);
+ if (spd.nr_pages <= 0)
+ return spd.nr_pages;
+
+ return splice_to_pipe(pipe, &spd);
+}
+
+asmlinkage long sys_vmsplice(int fd, const struct iovec __user *iov,
+ unsigned long nr_segs, unsigned int flags)
+{
+ struct file *file;
+ long error;
+ int fput;
+
+ error = -EBADF;
+ file = fget_light(fd, &fput);
+ if (file) {
+ if (file->f_mode & FMODE_WRITE)
+ error = do_vmsplice(file, iov, nr_segs, flags);
+
+ fput_light(file, fput);
+ }
+
+ return error;
+}
+
+asmlinkage long sys_splice(int fd_in, loff_t __user *off_in,
+ int fd_out, loff_t __user *off_out,
+ size_t len, unsigned int flags)