Make qemu_peek_buffer loop until it gets it's data

Make qemu_peek_buffer repeatedly call fill_buffer until it gets
all the data it requires, or until there is an error.

  At the moment, qemu_peek_buffer will try one qemu_fill_buffer if there
  isn't enough data waiting, however the kernel is entitled to return
  just a few bytes, and still leave qemu_peek_buffer with less bytes
  than it needed.  I've seen this fail in a dev world, and I think it
  could theoretically fail in the peeking of the subsection headers in
  the current world.

Comment qemu_peek_byte to point out it's not guaranteed to work for
  non-continuous peeks

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: ChenLiang <chenliang0016@icloud.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/migration/qemu-file.h b/include/migration/qemu-file.h
index a191fb6d8d..c90f5298ab 100644
--- a/include/migration/qemu-file.h
+++ b/include/migration/qemu-file.h
@@ -123,6 +123,11 @@ void qemu_put_be32(QEMUFile *f, unsigned int v);
 void qemu_put_be64(QEMUFile *f, uint64_t v);
 int qemu_peek_buffer(QEMUFile *f, uint8_t *buf, int size, size_t offset);
 int qemu_get_buffer(QEMUFile *f, uint8_t *buf, int size);
+/*
+ * Note that you can only peek continuous bytes from where the current pointer
+ * is; you aren't guaranteed to be able to peak to +n bytes unless you've
+ * previously peeked +n-1.
+ */
 int qemu_peek_byte(QEMUFile *f, int offset);
 int qemu_get_byte(QEMUFile *f);
 void qemu_file_skip(QEMUFile *f, int size);