[Qemu-devel] [PATCH] char: fix handling of QIO_CHANNEL_ERR_BLOCK

[Qemu-devel] [PATCH] char: fix handling of QIO_CHANNEL_ERR_BLOCK

[Daniel P. Berrange]

If io_channel_send_full gets QIO_CHANNEL_ERR_BLOCK it
and has already sent some of the data, it should return
that amount of data, not EAGAIN, as that would cause
the caller to re-try already sent data.

Unfortunately due to a previous rebase conflict resolution
error, the code for dealing with this was in the wrong
part of the conditional, and so mistakenly ran on other
I/O errors.

This be seen running

   qemu-system-x86_64 -monitor stdio

and entering 'info mtree', when running on a slow console
(eg a slow remote ssh session). The monitor would get into
an indefinite loop writing the same data until it managed
to send it all without getting EAGAIN.

Reported-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 qemu-char.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/qemu-char.c b/qemu-char.c
index 1b7d5da..c2e24a5 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -896,13 +896,13 @@ static int io_channel_send_full(QIOChannel *ioc,
             ioc, &iov, 1,
             fds, nfds, NULL);
         if (ret == QIO_CHANNEL_ERR_BLOCK) {
-            errno = EAGAIN;
-            return -1;
-        } else if (ret < 0) {
             if (offset) {
                 return offset;
             }
 
+            errno = EAGAIN;
+            return -1;
+        } else if (ret < 0) {
             errno = EINVAL;
             return -1;
         }
-- 
2.5.0

Re: [Qemu-devel] [PATCH] char: fix handling of QIO_CHANNEL_ERR_BLOCK

[Paolo Bonzini]

On 12/02/2016 15:46, Daniel P. Berrange wrote:
> If io_channel_send_full gets QIO_CHANNEL_ERR_BLOCK it
> and has already sent some of the data, it should return
> that amount of data, not EAGAIN, as that would cause
> the caller to re-try already sent data.
> 
> Unfortunately due to a previous rebase conflict resolution
> error, the code for dealing with this was in the wrong
> part of the conditional, and so mistakenly ran on other
> I/O errors.
> 
> This be seen running
> 
>    qemu-system-x86_64 -monitor stdio
> 
> and entering 'info mtree', when running on a slow console
> (eg a slow remote ssh session). The monitor would get into
> an indefinite loop writing the same data until it managed
> to send it all without getting EAGAIN.
> 
> Reported-by: Igor Mammedov <imammedo@redhat.com>
> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
> ---
>  qemu-char.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/qemu-char.c b/qemu-char.c
> index 1b7d5da..c2e24a5 100644
> --- a/qemu-char.c
> +++ b/qemu-char.c
> @@ -896,13 +896,13 @@ static int io_channel_send_full(QIOChannel *ioc,
>              ioc, &iov, 1,
>              fds, nfds, NULL);
>          if (ret == QIO_CHANNEL_ERR_BLOCK) {
> -            errno = EAGAIN;
> -            return -1;
> -        } else if (ret < 0) {
>              if (offset) {
>                  return offset;
>              }
>  
> +            errno = EAGAIN;
> +            return -1;
> +        } else if (ret < 0) {
>              errno = EINVAL;
>              return -1;
>          }
> 

Queued, thanks.

Paolo