From: Nikolay Shirokovskiy <nshirokovskiy@virtuozzo.com>
Date: Thu, 7 Sep 2017 07:44:15 +0000 (+0300)
Subject: iohelper: reduce zero-out in align case
X-Git-Tag: v3.8.0-rc1~87
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=776b9ac594b6a1e4afc924826c6e9cb5474e8e27;p=thirdparty%2Flibvirt.git

iohelper: reduce zero-out in align case

We only need to zero-out bytes that will be written.
May be we even don't need to zero-out at all because
of immediate truncate.
---

diff --git a/src/util/iohelper.c b/src/util/iohelper.c
index 1896fd362a..fe15a92e6c 100644
--- a/src/util/iohelper.c
+++ b/src/util/iohelper.c
@@ -120,10 +120,11 @@ runIO(const char *path, int fd, int oflags)
 
         /* handle last write size align in direct case */
         if (got < buflen && direct && fdout == fd) {
-            memset(buf + got, 0, buflen - got);
-            got = (got + alignMask) & ~alignMask;
+            ssize_t aligned_got = (got + alignMask) & ~alignMask;
 
-            if (safewrite(fdout, buf, got) < 0) {
+            memset(buf + got, 0, aligned_got - got);
+
+            if (safewrite(fdout, buf, aligned_got) < 0) {
                 virReportSystemError(errno, _("Unable to write %s"), fdoutname);
                 goto cleanup;
             }