Re: [PATCH 1/4] qemu-file: Don't do IO after shutdown

[Dr. David Alan Gilbert]

* Dr. David Alan Gilbert (address@hidden) wrote:
> * Juan Quintela (address@hidden) wrote:
> > Be sure that we are not doing neither read/write after shutdown of the
> > QEMUFile.
> > 
> > Signed-off-by: Juan Quintela <address@hidden>
> > ---
> >  migration/qemu-file.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/migration/qemu-file.c b/migration/qemu-file.c
> > index 26fb25ddc1..1e5543a279 100644
> > --- a/migration/qemu-file.c
> > +++ b/migration/qemu-file.c
> > @@ -53,6 +53,8 @@ struct QEMUFile {
> >  
> >      int last_error;
> >      Error *last_error_obj;
> > +    /* has the file has been shutdown */
> > +    bool shutdown;
> >  };
> >  
> >  /*
> > @@ -61,6 +63,7 @@ struct QEMUFile {
> >   */
> >  int qemu_file_shutdown(QEMUFile *f)
> >  {
> > +    f->shutdown = true;
> >      if (!f->ops->shut_down) {
> >          return -ENOSYS;
> >      }
> > @@ -214,6 +217,9 @@ void qemu_fflush(QEMUFile *f)
> >          return;
> >      }
> >  
> > +    if (f->shutdown) {
> > +        return;
> > +    }
> 
> OK, I did wonder if you need to free the iovec.
> 
> >      if (f->iovcnt > 0) {
> >          expect = iov_size(f->iov, f->iovcnt);
> >          ret = f->ops->writev_buffer(f->opaque, f->iov, f->iovcnt, f->pos,
> > @@ -328,6 +334,10 @@ static ssize_t qemu_fill_buffer(QEMUFile *f)
> >      f->buf_index = 0;
> >      f->buf_size = pending;
> >  
> > +    if (f->shutdown) {
> > +        return 0;
> > +    }
> 
> I also wondered if perhaps an error would be reasonable here; but I'm
> not sure what a read(2) does after a shutdown(2).
> 
> Still,
> 
> 
> Reviewed-by: Dr. David Alan Gilbert <address@hidden>

Actually, it turns out this breaks an assumption - 'shutdown' must cause
reads/writes/etc to fail and for the qemu_file to go into error state.
There's a few places we loop doing IO until we either change migration
state or the file goes into error.


diff --git a/migration/qemu-file.c b/migration/qemu-file.c
index 1e5543a279..bbb2b63927 100644
--- a/migration/qemu-file.c
+++ b/migration/qemu-file.c
@@ -63,11 +63,18 @@ struct QEMUFile {
  */
 int qemu_file_shutdown(QEMUFile *f)
 {
+    int ret;
+
     f->shutdown = true;
     if (!f->ops->shut_down) {
         return -ENOSYS;
     }
-    return f->ops->shut_down(f->opaque, true, true, NULL);
+    ret = f->ops->shut_down(f->opaque, true, true, NULL);
+
+    if (!f->last_error) {
+        qemu_file_set_error(f, -EIO);
+    }
+    return ret;
 }
 
 /*


seems to fix it for me.

Dave

> >      len = f->ops->get_buffer(f->opaque, f->buf + pending, f->pos,
> >                               IO_BUF_SIZE - pending, &local_error);
> >      if (len > 0) {
> > @@ -642,6 +652,9 @@ int64_t qemu_ftell(QEMUFile *f)
> >  
> >  int qemu_file_rate_limit(QEMUFile *f)
> >  {
> > +    if (f->shutdown) {
> > +        return 1;
> > +    }
> >      if (qemu_file_get_error(f)) {
> >          return 1;
> >      }
> > -- 
> > 2.23.0
> > 
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK
> 
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK