From: Daniel P. Berrangé <berrange@redhat.com>
Date: Tue, 10 Jun 2025 12:36:42 +0000 (+0100)
Subject: chardev/char-fd: skip automatic zero-init of large array
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=a503bdc22b91869e3bf45522e36b122889465306;p=thirdparty%2Fqemu.git

chardev/char-fd: skip automatic zero-init of large array

The 'fd_chr_read' method has a 4k byte array used for copying
data between the socket and device. Skip the automatic zero-init
of this array to eliminate the performance overhead in the I/O
hot path.

The 'buf' array will be fully initialized when reading data off
the network socket.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20250610123709.835102-5-berrange@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---

diff --git a/chardev/char-fd.c b/chardev/char-fd.c
index 23bfe3c0b1..6f03adf872 100644
--- a/chardev/char-fd.c
+++ b/chardev/char-fd.c
@@ -50,7 +50,7 @@ static gboolean fd_chr_read(QIOChannel *chan, GIOCondition cond, void *opaque)
     Chardev *chr = CHARDEV(opaque);
     FDChardev *s = FD_CHARDEV(opaque);
     int len;
-    uint8_t buf[CHR_READ_BUF_LEN];
+    QEMU_UNINITIALIZED uint8_t buf[CHR_READ_BUF_LEN];
     ssize_t ret;
 
     len = sizeof(buf);