[PATCH v2 04/10] vhost: modify vhost_log_write() for broader users

[Dongli Zhang <dongli.zhang@oracle.com>]

Currently, the only user of vhost_log_write() is vhost-net. The 'len'
argument prevents logging of pages that are not tainted by the RX path.

Adjustments are needed since more drivers (i.e. vhost-scsi) begin using
vhost_log_write(). So far vhost-net RX path may only partially use pages
shared by the last vring descriptor. Unlike vhost-net, vhost-scsi always
logs all pages shared via vring descriptors. To accommodate this, a new
argument 'partial' is introduced. This argument works alongside 'len' to
indicate whether the driver should log all pages of a vring descriptor, or
only pages that are tainted by the driver.

In addition, removes BUG().

Suggested-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
---
 drivers/vhost/net.c   |  2 +-
 drivers/vhost/vhost.c | 28 +++++++++++++++++-----------
 drivers/vhost/vhost.h |  2 +-
 3 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index b9b9e9d40951..0e5d82bfde76 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -1219,7 +1219,7 @@ static void handle_rx(struct vhost_net *net)
 		if (nvq->done_idx > VHOST_NET_BATCH)
 			vhost_net_signal_used(nvq);
 		if (unlikely(vq_log))
-			vhost_log_write(vq, vq_log, log, vhost_len,
+			vhost_log_write(vq, vq_log, log, vhost_len, true,
 					vq->iov, in);
 		total_len += vhost_len;
 	} while (likely(!vhost_exceeds_weight(vq, ++recv_pkts, total_len)));
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 9ac25d08f473..db3b30aba940 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2304,8 +2304,14 @@ static int log_used(struct vhost_virtqueue *vq, u64 used_offset, u64 len)
 	return 0;
 }
 
-int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
-		    unsigned int log_num, u64 len, struct iovec *iov, int count)
+/*
+ * 'len' is used only when 'partial' is true, to indicate whether the
+ * entire length of each descriptor is logged.
+ */
+int vhost_log_write(struct vhost_virtqueue *vq,
+		    struct vhost_log *log, unsigned int log_num,
+		    u64 len, bool partial,
+		    struct iovec *iov, int count)
 {
 	int i, r;
 
@@ -2323,19 +2329,19 @@ int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
 	}
 
 	for (i = 0; i < log_num; ++i) {
-		u64 l = min(log[i].len, len);
+		u64 l = partial ? min(log[i].len, len) : log[i].len;
+
 		r = log_write(vq->log_base, log[i].addr, l);
 		if (r < 0)
 			return r;
-		len -= l;
-		if (!len) {
-			if (vq->log_ctx)
-				eventfd_signal(vq->log_ctx);
-			return 0;
-		}
+
+		if (partial)
+			len -= l;
 	}
-	/* Length written exceeds what we have stored. This is a bug. */
-	BUG();
+
+	if (vq->log_ctx)
+		eventfd_signal(vq->log_ctx);
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(vhost_log_write);
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index bb75a292d50c..5de5941988fe 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -224,7 +224,7 @@ bool vhost_vq_avail_empty(struct vhost_dev *, struct vhost_virtqueue *);
 bool vhost_enable_notify(struct vhost_dev *, struct vhost_virtqueue *);
 
 int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
-		    unsigned int log_num, u64 len,
+		    unsigned int log_num, u64 len, bool partial,
 		    struct iovec *iov, int count);
 int vq_meta_prefetch(struct vhost_virtqueue *vq);
 
-- 
2.39.3