[PATCH v8 5/7] xen/console: use memcpy() in conring_puts()

[dmukhin@xxxxxxxx]

From: Denis Mukhin <dmukhin@xxxxxxxx> 

Make conring_puts() more efficient by using memcpy()'s, rather than
copying the ring a byte at a time.

No functional change intended.

Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>
---
Changes since v7:
- hardended len check in conring_puts()
---
 xen/drivers/char/console.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index 09282a7a4f8e..a1b8e5f5b507 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -361,12 +361,24 @@ static DECLARE_SOFTIRQ_TASKLET(conring_tasklet, 
conring_notify, NULL);
 /* NB: Do not send conring VIRQs during panic. */
 static bool conring_no_notify;
 
-static void conring_puts(const char *str, size_t len)
+static void conring_puts(const char *str, unsigned int len)
 {
+    unsigned int src = len;
+
+    /* There are no callers with strings longer than PAGE_SIZE. */
+    BUG_ON(len > PAGE_SIZE);
     ASSERT(rspin_is_locked(&console_lock));
 
-    while ( len-- )
-        conring[CONRING_IDX_MASK(conringp++)] = *str++;
+    while ( src < len )
+    {
+        unsigned int dst = CONRING_IDX_MASK(conringp + src);
+        unsigned int n = min(conring_size - dst, len - src);
+
+        memcpy(&conring[dst], &str[src], n);
+        src += n;
+    }
+
+    conringp += len;
 
     if ( conringp - conringc > conring_size )
         conringc = conringp - conring_size;
-- 
2.54.0