On Mon, 24 Sep 2012 14:27:17 +0800
Wen Congyang <we...@cn.fujitsu.com> wrote:
> At 09/22/2012 01:07 AM, Luiz Capitulino Wrote:
> > fd_write_vmcore() will indefinitely spin for a non-blocking
> > file-descriptor that would block. However, if the fd is non-blocking,
> > how does it make sense to spin?
> >
> > Change this behavior to return an error instead.
> >
> > Note that this can only happen with an fd provided by a management
> > application. The fd opened internally by dump-guest-memory is blocking.
> >
> > Signed-off-by: Luiz Capitulino <lcapitul...@redhat.com>
> > ---
> > dump.c | 13 +++----------
> > 1 file changed, 3 insertions(+), 10 deletions(-)
> >
> > diff --git a/dump.c b/dump.c
> > index 2bf8d8d..5eea015 100644
> > --- a/dump.c
> > +++ b/dump.c
> > @@ -100,18 +100,11 @@ static void dump_error(DumpState *s, const char
> > *reason)
> > static int fd_write_vmcore(void *buf, size_t size, void *opaque)
> > {
> > DumpState *s = opaque;
> > - int fd = s->fd;
> > size_t writen_size;
> >
> > - /* The fd may be passed from user, and it can be non-blocked */
> > - while (size) {
> > - writen_size = qemu_write_full(fd, buf, size);
> > - if (writen_size != size && errno != EAGAIN) {
>
> Hmm, if the fd is a blocking fd, errno can't be EAGAIN. So the
> function doesn't spin. What problems do you meet?
The problem is with non-blocking fds, where spinning isn't correct, for
two reasons:
1. If the fd is non-blocking, that means you don't want to block
and spinning for a long time will have the same effects
2. Spinning consumes host resources
