[Qemu-devel] [PATCH 3/5] sclpconsole: remove bogus check for -EAGAIN

["Daniel P. Berrange" <berrange@redhat.com>]

The write_console_data() method in sclpconsole-lm.c checks
whether the return value of qemu_chr_fe_write() has the
value of -EAGAIN and if so then increments the buffer offset
by the value of EAGAIN. Fortunately qemu_chr_fe_write() will
never return EAGAIN directly, rather it returns -1 with
errno set to EAGAIN, so this broken code path was not
reachable. The behaviour on EAGAIN was stil bad though,
causing the write_console_data() to busy_wait repeatedly
calling qemu_chr_fe_write() with no sleep between iters.

Just remove all this loop logic and replace with a call
to qemu_chr_fe_write_all().

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 hw/char/sclpconsole-lm.c | 18 +++---------------
 1 file changed, 3 insertions(+), 15 deletions(-)

diff --git a/hw/char/sclpconsole-lm.c b/hw/char/sclpconsole-lm.c
index a22ad8d..8cb0026 100644
--- a/hw/char/sclpconsole-lm.c
+++ b/hw/char/sclpconsole-lm.c
@@ -201,21 +201,9 @@ static int write_console_data(SCLPEvent *event, const uint8_t *buf, int len)
         return len;
     }
 
-    buf_offset = buf;
-    while (len > 0) {
-        ret = qemu_chr_fe_write(scon->chr, buf, len);
-        if (ret == 0) {
-            /* a pty doesn't seem to be connected - no error */
-            len = 0;
-        } else if (ret == -EAGAIN || (ret > 0 && ret < len)) {
-            len -= ret;
-            buf_offset += ret;
-        } else {
-            len = 0;
-        }
-    }
-
-    return ret;
+    /* XXX this blocks entire thread. Rewrite to use
+     * qemu_chr_fe_write and background I/O callbacks */
+    return qemu_chr_fe_write_all(scon->chr, buf, len);
 }
 
 static int process_mdb(SCLPEvent *event, MDBO *mdbo)
-- 
2.7.4