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Re: [Qemu-devel] [PATCH 03/20] char: add IOWatchPoll support
From: |
Amit Shah |
Subject: |
Re: [Qemu-devel] [PATCH 03/20] char: add IOWatchPoll support |
Date: |
Fri, 29 Mar 2013 21:38:55 +0530 |
On (Fri) 29 Mar 2013 [09:03:10], Anthony Liguori wrote:
> Amit Shah <address@hidden> writes:
>
> > On (Fri) 29 Mar 2013 [07:24:07], Anthony Liguori wrote:
> >> Amit Shah <address@hidden> writes:
> >>
> >> > On (Tue) 05 Mar 2013 [23:21:18], Amit Shah wrote:
> >> >> From: Anthony Liguori <address@hidden>
> >> >>
> >> >> This is a special GSource that supports CharDriverState style
> >> >> poll callbacks.
> >> >>
> >> >> For reviewability and bisectability, this code is #if 0'd out in this
> >> >> patch to avoid unused warnings since all of the functions are static.
> >> >>
> >> >> Signed-off-by: Anthony Liguori <address@hidden>
> >> >> Signed-off-by: Amit Shah <address@hidden>
> >> >
> >> >
> >> >> +static int io_channel_send_all(GIOChannel *fd, const void *_buf, int
> >> >> len1)
> >> >> +{
> >> >> + GIOStatus status;
> >> >> + gsize bytes_written;
> >> >> + int len;
> >> >> + const uint8_t *buf = _buf;
> >> >> +
> >> >> + len = len1;
> >> >> + while (len > 0) {
> >> >> + status = g_io_channel_write_chars(fd, (const gchar *)buf, len,
> >> >> + &bytes_written, NULL);
> >> >> + if (status != G_IO_STATUS_NORMAL) {
> >> >> + if (status != G_IO_STATUS_AGAIN) {
> >> >> + return -1;
> >> >> + }
> >> >
> >> > It's not quite right to return -1 here; previous iterations of the
> >> > while loop could have successfully written data, and (len1 - len)
> >> > could be +ve.
> >>
> >> Once -1 is returned, it's a terminal error. It doesn't matter that we
> >> may have written some data.
> >
> > Why do you say that?
>
> Because you're quoting the wrong patch :-)
Indeed.
> This bit is rewritten by a
> later patch which is the source of your problem below. In the patch you
> quote, we busy spin until all data is written. However, with:
>
> commit 23673ca740e0eda66901ca801a5a901df378b063
> Author: Anthony Liguori <address@hidden>
> Date: Tue Mar 5 23:21:23 2013 +0530
>
> qemu-char: add watch support
>
> We started to return EAGAIN even if we have a partially successful
> write. I'm running a patch through testing right now that rewrites this
> function to have sane semantics (return bytes written on partial write).
Yes, that's where the problem is: EINTR and EAGAIN returns.
> I'll post as soon as testing completes.
Thanks!
Amit
[Qemu-devel] [PATCH 04/20] qemu-char: convert fd_chr to use a GIOChannel, Amit Shah, 2013/03/05
[Qemu-devel] [PATCH 05/20] qemu-char: convert pty to GIOChannel, Amit Shah, 2013/03/05
[Qemu-devel] [PATCH 06/20] qemu-char: convert UDP to GIOChannel, Amit Shah, 2013/03/05
[Qemu-devel] [PATCH 07/20] qemu-char: tcp: make use GIOChannel, Amit Shah, 2013/03/05
[Qemu-devel] [PATCH 08/20] qemu-char: add watch support, Amit Shah, 2013/03/05
[Qemu-devel] [PATCH 09/20] qemu-char: add pty watch, Amit Shah, 2013/03/05
[Qemu-devel] [PATCH 10/20] char: add gio watch fn for tcp backends, Amit Shah, 2013/03/05
[Qemu-devel] [PATCH 11/20] qemu-char: use a glib timeout instead of qemu-timer, Amit Shah, 2013/03/05