Re: [Qemu-devel] [PATCH 3/3] add live dumping capability

[Paolo Bonzini]

On 07/09/2009 04:43 PM, Anthony Liguori wrote:
> Paolo Bonzini wrote:
> > > > With the previous cleanups in place, it is easy to trigger
> > > > restart when the state machine goes from the COMPLETING to the
> > > > COMPLETED state. Besides this, the patch is just simple
> > > > scaffolding for the monitor command and to migrate to a file
> > > > rather than a pipe (which is a bit simpler because we do not
> > > > need non-blocking I/O).
> > >
> > > Then this isn't live migration.
> >
> > Sorry, I cannot understand this remark.
>
> You're using blocking I/O which will cause the guest to pause while disk
> I/O is happening.

Unfortunately non-blocking I/O does not work with files (it works with 
named pipes of course, so it would have been a good idea to keep it):

$ cat f.c
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>

int main()
{
  int f = open("f.txt", O_CREAT|O_WRONLY, 0666);
  fcntl (f, F_SETFL, fcntl (f, F_GETFL) | O_NONBLOCK);
  char *m = malloc (1 << 28);
  write (f, m, 1 << 28);
}
$ gcc f.c
$ strace ./a.out
open("f.txt", O_WRONLY|O_CREAT, 0666)   = 3
fcntl(3, F_GETFL)                       = O_WRONLY|O_LARGEFILE
fcntl(3, F_SETFL, O_WRONLY|O_NONBLOCK|O_LARGEFILE) = 0
mmap(NULL, 268439552, ...) = 0x7f73634db000
write(3, "\0"..., 268435456) = <after quite some time> 268435456
$

Anyway, 3/3 is withdrawn since as far as libvirt is concerned I can use 
migrate+cont.  Do you have any comments on 1/3 and 2/3 to include them 
as cleanups, or you prefer to go with just your small patch to fix the 
unconditional restart after an error?

Paolo