On Wed, May 30 2007, Ingo Molnar wrote:
> - splice. (a bit too early to tell but it's looking good so far. Would
> be nice if someone did a brute-force memcpy() based vmsplice to user
> memory, just to make usage fully symmetric.)
Heh, I actually agree, at least then the interface is complete! We can
always replace it with something more clever, should someone feel so
inclined. Here's a rough patch to do that, it's totally untested (but it
compiles). sparse will warn about the __user removal, though. I'm sure
viro would shoot me dead on the spot, should he see this...
diff --git a/fs/splice.c b/fs/splice.c
index 12f2828..5023c01 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -657,9 +657,9 @@ out_ret:
* key here is the 'actor' worker passed in that actually moves the data
* to the wanted destination. See pipe_to_file/pipe_to_sendpage above.
*/
-ssize_t __splice_from_pipe(struct pipe_inode_info *pipe,
- struct file *out, loff_t *ppos, size_t len,
- unsigned int flags, splice_actor *actor)
+ssize_t __splice_from_pipe(struct pipe_inode_info *pipe, void *actor_priv,
+ loff_t *ppos, size_t len, unsigned int flags,
+ splice_actor *actor)
{
int ret, do_wakeup, err;
struct splice_desc sd;
@@ -669,7 +669,7 @@ ssize_t __splice_from_pipe(struct pipe_inode_info *pipe,
sd.total_len = len;
sd.flags = flags;
- sd.file = out;
+ sd.file = actor_priv;
sd.pos = *ppos;
for (;;) {
@@ -1240,28 +1240,104 @@ static int get_iovec_page_array(const struct iovec __user *iov,
return error;
}
+static int pipe_to_user(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
+ struct splice_desc *sd)
+{
+ int ret;
+
+ ret = buf->ops->pin(pipe, buf);
+ if (!ret) {
+ void __user *dst = sd->userptr;
+ /*
+ * use non-atomic map, can be optimized to map atomically if we
+ * prefault the user memory.
+ */
+ char *src = buf->ops->map(pipe, buf, 0);
+
+ if (copy_to_user(dst, src, sd->len))
+ ret = -EFAULT;
+
+ buf->ops->unmap(pipe, buf, src);
+
+ if (!ret)
+ return sd->len;
+ }
+
+ 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;
+ ssize_t size;
+ int error;
+ long ret;
+
+ pipe = pipe_info(file->f_path.dentry->d_inode);
+ if (!pipe)
+ return -EBADF;
+ if (!nr_segs)
+ return 0;
+
+ if (pipe->inode)
+ mutex_lock(&pipe->inode->i_mutex);
+
+ 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;
+ error = -EFAULT;
+ if (unlikely(!base))
+ break;
+
+ size = __splice_from_pipe(pipe, (void *) base, NULL, len,
+ flags, pipe_to_user);
+ if (size < 0) {
+ if (!ret)
+ ret = size;
+
+ break;
+ }
+
+ nr_segs--;
+ iov++;
+ ret += size;
+ }
+
+ if (pipe->inode)
+ mutex_unlock(&pipe->inode->i_mutex);
+
+ 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];
@@ -1289,6 +1365,22 @@ static long do_vmsplice(struct file *file, const struct iovec __user *iov,
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)
{
@@ -1300,7 +1392,9 @@ asmlinkage long sys_vmsplice(int fd, const struct iovec __user *iov,
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);
}
--
Jens Axboe
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