[Qemu-devel] [PATCH 4/5] I/O vector helpers

[Avi Kivity <avi@redhat.com>]

In general, it is not possible to predict the size of of an I/O vector since
a contiguous guest region may map to a disconiguous host region.  Add some
helpers to manage I/O vector growth.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
 qemu-common.h |   10 ++++++++++
 vl.c          |   25 +++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 0 deletions(-)

diff --git a/qemu-common.h b/qemu-common.h
index d83e61b..1a746f9 100644
--- a/qemu-common.h
+++ b/qemu-common.h
@@ -191,6 +191,16 @@ int cpu_load(QEMUFile *f, void *opaque, int version_id);
 /* Force QEMU to stop what it's doing and service IO */
 void qemu_service_io(void);
 
+typedef struct QEMUIOVector {
+    struct iovec *iov;
+    int niov;
+    int nalloc;
+} QEMUIOVector;
+
+void qemu_iovec_init(QEMUIOVector *qiov, int alloc_hint);
+void qemu_iovec_add(QEMUIOVector *qiov, void *base, size_t len);
+void qemu_iovec_destroy(QEMUIOVector *qiov);
+
 #endif /* dyngen-exec.h hack */
 
 #endif
diff --git a/vl.c b/vl.c
index 34ddc07..7ceedd4 100644
--- a/vl.c
+++ b/vl.c
@@ -3344,6 +3344,31 @@ static void qemu_bh_update_timeout(int *timeout)
     }
 }
 
+/* io vectors */
+
+void qemu_iovec_init(QEMUIOVector *qiov, int alloc_hint)
+{
+    qiov->iov = qemu_malloc(alloc_hint * sizeof(struct iovec));
+    qiov->niov = 0;
+    qiov->nalloc = alloc_hint;
+}
+
+void qemu_iovec_add(QEMUIOVector *qiov, void *base, size_t len)
+{
+    if (qiov->niov == qiov->nalloc) {
+        qiov->nalloc = 2 * qiov->nalloc + 1;
+        qiov->iov = qemu_realloc(qiov->iov, qiov->nalloc * sizeof(struct iovec));
+    }
+    qiov->iov[qiov->niov].iov_base = base;
+    qiov->iov[qiov->niov].iov_len = len;
+    ++qiov->niov;
+}
+
+void qemu_iovec_destroy(QEMUIOVector *qiov)
+{
+    qemu_free(qiov->iov);
+}
+
 /***********************************************************/
 /* machine registration */
 
-- 
1.6.0.6