Re: [PATCH -mm 4/10][RFC] aio: convert aio_complete to file_endio_t

On 1/15/07, David Brownell [off-list ref] wrote:

On Monday 15 January 2007 5:54 pm, Nate Diller wrote:

quoted

--- a/drivers/usb/gadget/inode.c      2007-01-12 14:42:29.000000000 -0800
+++ b/drivers/usb/gadget/inode.c      2007-01-12 14:25:34.000000000 -0800

@@ -559,35 +559,32 @@ static int ep_aio_cancel(struct kiocb *i
      return value;
 }

-static ssize_t ep_aio_read_retry(struct kiocb *iocb)
+static int ep_aio_read_retry(struct kiocb *iocb)
 {
      struct kiocb_priv       *priv = iocb->private;
-     ssize_t                 len, total;
-     int                     i;
+     ssize_t                 total;
+     int                     i, err = 0;

      /* we "retry" to get the right mm context for this: */

      /* copy stuff into user buffers */
      total = priv->actual;
-     len = 0;
      for (i=0; i < priv->nr_segs; i++) {
              ssize_t this = min((ssize_t)(priv->iv[i].iov_len), total);

              if (copy_to_user(priv->iv[i].iov_base, priv->buf, this)) {
-                     if (len == 0)
-                             len = -EFAULT;
+                     err = -EFAULT;

Discarding the capability to report partial success, e.g. that the first N
bytes were properly transferred?  I don't see any virtue in that change.
Quite the opposite in fact.

I think you're also expecting that if N bytes were requested, that's always
how many will be received.  That's not true for packetized I/O such as USB
isochronous transfers ... where it's quite legit (and in some cases routine)
for the other end to send packets that are shorter than the maximum allowed.
Sending a zero length packet is not the same as sending no packet at all,
for another example.

I will convert this (usb) code to use the standard completion path,
which you will notice *gained* the ability to properly report both an
error and a partial success as part of this patch.  In fact, fixing
this up was my intention when I wrote this patch, and the later patch
was a compromise intended to get this whole bundle out for review in a
timely manner :)

NATE