vmsplice: add vmsplice-to-user support
A bit of a cheat, it actually just copies the data to userspace. But
this makes the interface nice and symmetric and enables people to build
on splice, with room for future improvement in performance.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fs/splice.c b/fs/splice.c
index 68f6328..13846f7 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -528,7 +528,7 @@
static int pipe_to_sendpage(struct pipe_inode_info *pipe,
struct pipe_buffer *buf, struct splice_desc *sd)
{
- struct file *file = sd->file;
+ struct file *file = sd->u.file;
loff_t pos = sd->pos;
int ret, more;
@@ -566,7 +566,7 @@
static int pipe_to_file(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
struct splice_desc *sd)
{
- struct file *file = sd->file;
+ struct file *file = sd->u.file;
struct address_space *mapping = file->f_mapping;
unsigned int offset, this_len;
struct page *page;
@@ -769,7 +769,7 @@
.total_len = len,
.flags = flags,
.pos = *ppos,
- .file = out,
+ .u.file = out,
};
/*
@@ -807,7 +807,7 @@
.total_len = len,
.flags = flags,
.pos = *ppos,
- .file = out,
+ .u.file = out,
};
ssize_t ret;
int err;
@@ -1087,7 +1087,7 @@
static int direct_splice_actor(struct pipe_inode_info *pipe,
struct splice_desc *sd)
{
- struct file *file = sd->file;
+ struct file *file = sd->u.file;
return do_splice_from(pipe, file, &sd->pos, sd->total_len, sd->flags);
}
@@ -1100,7 +1100,7 @@
.total_len = len,
.flags = flags,
.pos = *ppos,
- .file = out,
+ .u.file = out,
};
size_t ret;
@@ -1289,28 +1289,131 @@
return error;
}
+static int pipe_to_user(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
+ struct splice_desc *sd)
+{
+ char *src;
+ int ret;
+
+ ret = buf->ops->pin(pipe, buf);
+ if (unlikely(ret))
+ return ret;
+
+ /*
+ * See if we can use the atomic maps, by prefaulting in the
+ * pages and doing an atomic copy
+ */
+ if (!fault_in_pages_writeable(sd->u.userptr, sd->len)) {
+ src = buf->ops->map(pipe, buf, 1);
+ ret = __copy_to_user_inatomic(sd->u.userptr, src + buf->offset,
+ sd->len);
+ buf->ops->unmap(pipe, buf, src);
+ if (!ret) {
+ ret = sd->len;
+ goto out;
+ }
+ }
+
+ /*
+ * No dice, use slow non-atomic map and copy
+ */
+ src = buf->ops->map(pipe, buf, 0);
+
+ ret = sd->len;
+ if (copy_to_user(sd->u.userptr, src + buf->offset, sd->len))
+ ret = -EFAULT;
+
+out:
+ if (ret > 0)
+ sd->u.userptr += ret;
+ buf->ops->unmap(pipe, buf, src);
+ return ret;
+}
+
+/*
+ * For lack of a better implementation, implement vmsplice() to userspace
+ * as a simple copy of the pipes pages to the user iov.
+ */
+static long vmsplice_to_user(struct file *file, const struct iovec __user *iov,
+ unsigned long nr_segs, unsigned int flags)
+{
+ struct pipe_inode_info *pipe;
+ struct splice_desc sd;
+ ssize_t size;
+ int error;
+ long ret;
+
+ pipe = pipe_info(file->f_path.dentry->d_inode);
+ if (!pipe)
+ return -EBADF;
+
+ if (pipe->inode)
+ mutex_lock(&pipe->inode->i_mutex);
+
+ error = ret = 0;
+ while (nr_segs) {
+ void __user *base;
+ size_t len;
+
+ /*
+ * 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;
+ if (unlikely(!base)) {
+ error = -EFAULT;
+ break;
+ }
+
+ sd.len = 0;
+ sd.total_len = len;
+ sd.flags = flags;
+ sd.u.userptr = base;
+ sd.pos = 0;
+
+ size = __splice_from_pipe(pipe, &sd, pipe_to_user);
+ if (size < 0) {
+ if (!ret)
+ ret = size;
+
+ break;
+ }
+
+ ret += size;
+
+ if (size < len)
+ break;
+
+ nr_segs--;
+ iov++;
+ }
+
+ if (pipe->inode)
+ mutex_unlock(&pipe->inode->i_mutex);
+
+ if (!ret)
+ ret = error;
+
+ return ret;
+}
+
/*
* 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)
+static long vmsplice_to_pipe(struct file *file, const struct iovec __user *iov,
+ unsigned long nr_segs, unsigned int flags)
{
struct pipe_inode_info *pipe;
struct page *pages[PIPE_BUFFERS];
@@ -1325,10 +1428,6 @@
pipe = pipe_info(file->f_path.dentry->d_inode);
if (!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);
@@ -1338,6 +1437,22 @@
return splice_to_pipe(pipe, &spd);
}
+/*
+ * Note that vmsplice only really supports true 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).
+ *
+ * Currently we punt and implement it as a normal copy, see pipe_to_user().
+ *
+ */
asmlinkage long sys_vmsplice(int fd, const struct iovec __user *iov,
unsigned long nr_segs, unsigned int flags)
{
@@ -1345,11 +1460,18 @@
long error;
int fput;
+ if (unlikely(nr_segs > UIO_MAXIOV))
+ return -EINVAL;
+ else if (unlikely(!nr_segs))
+ return 0;
+
error = -EBADF;
file = fget_light(fd, &fput);
if (file) {
if (file->f_mode & FMODE_WRITE)
- error = do_vmsplice(file, iov, nr_segs, flags);
+ error = vmsplice_to_pipe(file, iov, nr_segs, flags);
+ else if (file->f_mode & FMODE_READ)
+ error = vmsplice_to_user(file, iov, nr_segs, flags);
fput_light(file, fput);
}