Add a possibility of embedded iovec, for cases when we need only one
local iov.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
---
include/qemu/iov.h | 47 ++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 45 insertions(+), 2 deletions(-)
diff --git a/include/qemu/iov.h b/include/qemu/iov.h
index 5f433c7768..3753b63558 100644
--- a/include/qemu/iov.h
+++ b/include/qemu/iov.h
@@ -133,10 +133,53 @@ size_t iov_discard_back(struct iovec *iov, unsigned int
*iov_cnt,
typedef struct QEMUIOVector {
struct iovec *iov;
int niov;
- int nalloc;
- size_t size;
+
+ /*
+ * For external @iov (qemu_iovec_init_external()) or allocated @iov
+ * (qemu_iovec_init()) @size is the cumulative size of iovecs and
+ * @local_iov is invalid and unused.
+ *
+ * For embedded @iov (QEMU_IOVEC_INIT_BUF() or qemu_iovec_init_buf()),
+ * @iov is equal to &@local_iov, and @size is valid, as it has same
+ * offset and type as @local_iov.iov_len, which is guaranteed by
+ * static assertions below.
+ *
+ * @nalloc is valid always and is -1 both for embedded and external
+ * cases. It included into union only to make appropriate padding for
+ * @size field avoiding creation of 0-length array in the worst case.
+ */
+ union {
+ struct {
+ int nalloc;
+ struct iovec local_iov;
+ };
+ struct {
+ char __pad[sizeof(int) + offsetof(struct iovec, iov_len)];
+ size_t size;
+ };
+ };
} QEMUIOVector;
+QEMU_BUILD_BUG_ON(offsetof(QEMUIOVector, size) !=
+ offsetof(QEMUIOVector, local_iov.iov_len));
+
+#define QEMU_IOVEC_INIT_BUF(self, buf, len) \
+{ \
+ .iov = &(self).local_iov, \
+ .niov = 1, \
+ .nalloc = -1, \
+ .local_iov = { \
+ .iov_base = (void *)(buf), /* cast away const */ \
+ .iov_len = (len), \
+ }, \
+}
+
+static inline void qemu_iovec_init_buf(QEMUIOVector *qiov,
+ void *buf, size_t len)
+{
+ *qiov = (QEMUIOVector) QEMU_IOVEC_INIT_BUF(*qiov, buf, len);
+}
+
void qemu_iovec_init(QEMUIOVector *qiov, int alloc_hint);
void qemu_iovec_init_external(QEMUIOVector *qiov, struct iovec *iov, int niov);
void qemu_iovec_add(QEMUIOVector *qiov, void *base, size_t len);
--
2.18.0
