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stream: Add osmo_stream_srv_link_set_msgb_alloc_info()

This is needed so that user can set desired headroom+size info on
rx-allocated msgbs, so that osmo_stream_srv can inherit them upon
osmo_stream_srv_create2().

Manually obtaining the iofd through osmo_stream_srv_get_iofd() and
changing the params directly in the iofd produces undesired effects,
since the first msgbs are alredy allocated during
osmo_stream_srv_create2 (which calls osmo_iofd_register()) before the
object is available to the user.
As a result, first rx messages may come with unexpected size/headroom.

Ideally we'd had written the osmo_stream_srv APIs to have a 2 step
setup, eg _alloc() + _run()/_start(), but too late to do so now.
This approach is already follwed by existing
osmo_stream_srv_link_set_tx_queue_max_length() API.

Change-Id: I80a1c4b227629e3ca0c8c587a103db6057322cb4
---
M TODO-RELEASE
M include/osmocom/netif/stream.h
M src/stream_srv.c
3 files changed, 34 insertions(+), 0 deletions(-)

git pull ssh://gerrit.osmocom.org:29418/libosmo-netif refs/changes/69/39369/1

diff --git a/TODO-RELEASE b/TODO-RELEASE
index e66b421..dfdbd89 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -11,3 +11,4 @@
 libosmo-netif add API osmo-stream_cli_set_tx_queue_max_length(), osmo_stream_srv_link_set_tx_queue_max_length()
 libosmo-netif add API struct osmo_ipa_ka_fsm_inst
 libosmo-netif add API osmo_stream_{cli,srv}_set_segmentation_cb2()
+libosmo-netif add API osmo_stream_srv_link_set_msgb_alloc_info()
diff --git a/include/osmocom/netif/stream.h b/include/osmocom/netif/stream.h
index 2866ea3..951f42a 100644
--- a/include/osmocom/netif/stream.h
+++ b/include/osmocom/netif/stream.h
@@ -85,6 +85,7 @@
 char *osmo_stream_srv_link_get_sockname(const struct osmo_stream_srv_link *link);
 struct osmo_fd *osmo_stream_srv_link_get_ofd(struct osmo_stream_srv_link *link);
 int osmo_stream_srv_link_get_fd(const struct osmo_stream_srv_link *link);
+int osmo_stream_srv_link_set_msgb_alloc_info(struct osmo_stream_srv_link *link, unsigned int size, unsigned int headroom);
 bool osmo_stream_srv_link_is_opened(const struct osmo_stream_srv_link *link);
 int osmo_stream_srv_link_open(struct osmo_stream_srv_link *link);
 void osmo_stream_srv_link_close(struct osmo_stream_srv_link *link);
diff --git a/src/stream_srv.c b/src/stream_srv.c
index c2b187a..261539b 100644
--- a/src/stream_srv.c
+++ b/src/stream_srv.c
@@ -69,6 +69,15 @@
  * Server side.
  */
 
+struct msgb_alloc_info {
+		/*! Whether it was set by user or we use iofd defaults */
+		bool set_by_user;
+		/*! size of msgb to allocate (excluding headroom) */
+		unsigned int size;
+		/*! headroom to allocate when allocating msgb's */
+		unsigned int headroom;
+};
+
 #define OSMO_STREAM_SRV_F_RECONF	(1 << 0)
 #define OSMO_STREAM_SRV_F_NODELAY	(1 << 1)
 
@@ -88,6 +97,7 @@
 	void			*data;
 	int			flags;
 	unsigned int		tx_queue_max_length; /* Max amount of msgbs which can be enqueued */
+	struct msgb_alloc_info	msgb_alloc;
 	struct osmo_sock_init2_multiaddr_pars ma_pars;
 };
 
@@ -506,6 +516,26 @@
 	link->accept_cb = accept_cb;
 }
 
+/*! Set the msgb allocation parameters on child osmo_stream_srv objects
+ *  \param[in] link Stream Server Link
+ *  \param[in] size Size of msgb to allocate (excluding headroom)
+ *  \param[in] headroom Headroom to allocate when allocating msgb's
+ *
+ *  The parameters are applied to osmo_stream_srv objects upon creation.
+ *  Setting both to 0 leaves it as implementation default.
+ **/
+int osmo_stream_srv_link_set_msgb_alloc_info(struct osmo_stream_srv_link *link, unsigned int size, unsigned int headroom)
+{
+	if (size == 0 && headroom == 0) {
+		link->msgb_alloc.set_by_user = false;
+	} else {
+		link->msgb_alloc.set_by_user = true;
+		link->msgb_alloc.headroom = headroom;
+		link->msgb_alloc.size = size;
+	}
+	return 0;
+}
+
 /*! Destroy the stream server link. Closes + Releases Memory.
  *  \param[in] link Stream Server Link */
 void osmo_stream_srv_link_destroy(struct osmo_stream_srv_link *link)
@@ -962,6 +992,8 @@
 	}
 
 	osmo_iofd_set_txqueue_max_length(conn->iofd, conn->srv->tx_queue_max_length);
+	if (conn->srv->msgb_alloc.set_by_user)
+		osmo_iofd_set_alloc_info(conn->iofd, conn->srv->msgb_alloc.size, conn->srv->msgb_alloc.headroom);
 
 	if (osmo_iofd_register(conn->iofd, fd) < 0) {
 		LOGSSRV(conn, LOGL_ERROR, "could not register FD %d\n", fd);

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