splice: implement default splice_write method

If f_op->splice_write() is not implemented, fall back to a plain write.
Use vfs_writev() to write from the pipe buffers.

This will allow splice on all filesystems and file types.  This
includes "direct_io" files in fuse which bypass the page cache.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --git a/fs/splice.c b/fs/splice.c
index 3bd9cb21b38e91b34472e2e02f8c8a11e3237913..eefd96b1d7fbfdc7c5873ca45e551efffcf548e1 100644 (file)
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -535,6 +535,21 @@ static ssize_t kernel_readv(struct file *file, const struct iovec *vec,
        return res;
 }
 
+static ssize_t kernel_writev(struct file *file, const struct iovec *vec,
+                           unsigned long vlen, loff_t *ppos)
+{
+       mm_segment_t old_fs;
+       ssize_t res;
+
+       old_fs = get_fs();
+       set_fs(get_ds());
+       /* The cast to a user pointer is valid due to the set_fs() */
+       res = vfs_writev(file, (const struct iovec __user *)vec, vlen, ppos);
+       set_fs(old_fs);
+
+       return res;
+}
+
 ssize_t default_file_splice_read(struct file *in, loff_t *ppos,
                                 struct pipe_inode_info *pipe, size_t len,
                                 unsigned int flags)
@@ -988,6 +1003,122 @@ generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
 
 EXPORT_SYMBOL(generic_file_splice_write);
 
+static struct pipe_buffer *nth_pipe_buf(struct pipe_inode_info *pipe, int n)
+{
+       return &pipe->bufs[(pipe->curbuf + n) % PIPE_BUFFERS];
+}
+
+static ssize_t default_file_splice_write(struct pipe_inode_info *pipe,
+                                        struct file *out, loff_t *ppos,
+                                        size_t len, unsigned int flags)
+{
+       ssize_t ret = 0;
+       ssize_t total_len = 0;
+       int do_wakeup = 0;
+
+       pipe_lock(pipe);
+       while (len) {
+               struct pipe_buffer *buf;
+               void *data[PIPE_BUFFERS];
+               struct iovec vec[PIPE_BUFFERS];
+               unsigned int nr_pages = 0;
+               unsigned int write_len = 0;
+               unsigned int now_len = len;
+               unsigned int this_len;
+               int i;
+
+               BUG_ON(pipe->nrbufs > PIPE_BUFFERS);
+               for (i = 0; i < pipe->nrbufs && now_len; i++) {
+                       buf = nth_pipe_buf(pipe, i);
+
+                       ret = buf->ops->confirm(pipe, buf);
+                       if (ret)
+                               break;
+
+                       data[i] = buf->ops->map(pipe, buf, 0);
+                       this_len = min(buf->len, now_len);
+                       vec[i].iov_base = (void __user *) data[i] + buf->offset;
+                       vec[i].iov_len = this_len;
+                       now_len -= this_len;
+                       write_len += this_len;
+                       nr_pages++;
+               }
+
+               if (nr_pages) {
+                       ret = kernel_writev(out, vec, nr_pages, ppos);
+                       if (ret == 0)
+                               ret = -EIO;
+                       if (ret > 0) {
+                               len -= ret;
+                               total_len += ret;
+                       }
+               }
+
+               for (i = 0; i < nr_pages; i++) {
+                       buf = nth_pipe_buf(pipe, i);
+                       buf->ops->unmap(pipe, buf, data[i]);
+
+                       if (ret > 0) {
+                               this_len = min_t(unsigned, vec[i].iov_len, ret);
+                               buf->offset += this_len;
+                               buf->len -= this_len;
+                               ret -= this_len;
+                       }
+               }
+
+               if (ret < 0)
+                       break;
+
+               while (pipe->nrbufs) {
+                       const struct pipe_buf_operations *ops;
+
+                       buf = nth_pipe_buf(pipe, 0);
+                       if (buf->len)
+                               break;
+
+                       ops = buf->ops;
+                       buf->ops = NULL;
+                       ops->release(pipe, buf);
+                       pipe->curbuf = (pipe->curbuf + 1) % PIPE_BUFFERS;
+                       pipe->nrbufs--;
+                       if (pipe->inode)
+                               do_wakeup = 1;
+               }
+
+               if (pipe->nrbufs)
+                       continue;
+               if (!pipe->writers)
+                       break;
+               if (!pipe->waiting_writers) {
+                       if (total_len)
+                               break;
+               }
+
+               if (flags & SPLICE_F_NONBLOCK) {
+                       ret = -EAGAIN;
+                       break;
+               }
+
+               if (signal_pending(current)) {
+                       ret = -ERESTARTSYS;
+                       break;
+               }
+
+               if (do_wakeup) {
+                       wakeup_pipe_writers(pipe);
+                       do_wakeup = 0;
+               }
+
+               pipe_wait(pipe);
+       }
+       pipe_unlock(pipe);
+
+       if (do_wakeup)
+               wakeup_pipe_writers(pipe);
+
+       return total_len ? total_len : ret;
+}
+
 /**
  * generic_splice_sendpage - splice data from a pipe to a socket
  * @pipe:      pipe to splice from
@@ -1015,11 +1146,10 @@ EXPORT_SYMBOL(generic_splice_sendpage);
 static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
                           loff_t *ppos, size_t len, unsigned int flags)
 {
+       ssize_t (*splice_write)(struct pipe_inode_info *, struct file *,
+                               loff_t *, size_t, unsigned int);
        int ret;
 
-       if (unlikely(!out->f_op || !out->f_op->splice_write))
-               return -EINVAL;
-
        if (unlikely(!(out->f_mode & FMODE_WRITE)))
                return -EBADF;
 
@@ -1030,7 +1160,11 @@ static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
        if (unlikely(ret < 0))
                return ret;
 
-       return out->f_op->splice_write(pipe, out, ppos, len, flags);
+       splice_write = out->f_op->splice_write;
+       if (!splice_write)
+               splice_write = default_file_splice_write;
+
+       return splice_write(pipe, out, ppos, len, flags);
 }
 
 /*