[PATCH 1/1] platform: optimize sysctl_set() to use stack allocated buffer

[Thomas Haller <thaller redhat com>]

The value written to sysctl is usually a short string. It makes sense
to optimize for this case and avoid allocating a temporary string
on the heap.

An alternative would be to use writev(), which effectively does the same
and also creates a temporary buffer (preferably stack allocated).
---
 src/platform/nm-linux-platform.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/platform/nm-linux-platform.c b/src/platform/nm-linux-platform.c
index 1ebffd0..a1504d1 100644
--- a/src/platform/nm-linux-platform.c
+++ b/src/platform/nm-linux-platform.c
@@ -2452,8 +2452,11 @@ _log_dbg_sysctl_set_impl (NMPlatform *platform, const char *path, const char *va
 static gboolean
 sysctl_set (NMPlatform *platform, const char *path, const char *value)
 {
-       int fd, len, nwrote, tries;
+       int fd, tries;
+       gssize nwrote;
+       gsize len;
        char *actual;
+       gs_free char *actual_free = NULL;
 
        g_return_val_if_fail (path != NULL, FALSE);
        g_return_val_if_fail (value != NULL, FALSE);
@@ -2483,10 +2486,16 @@ sysctl_set (NMPlatform *platform, const char *path, const char *value)
         * sysctl support partial writes so the LF must be added to the string we're
         * about to write.
         */
-       actual = g_strdup_printf ("%s\n", value);
+       len = strlen (value) + 1;
+       if (len > 512)
+               actual = actual_free = g_malloc (len + 1);
+       else
+               actual = g_alloca (len + 1);
+       memcpy (actual, value, len - 1);
+       actual[len - 1] = '\n';
+       actual[len] = '\0';
 
        /* Try to write the entire value three times if a partial write occurs */
-       len = strlen (actual);
        for (tries = 0, nwrote = 0; tries < 3 && nwrote != len; tries++) {
                nwrote = write (fd, actual, len);
                if (nwrote == -1) {
@@ -2505,7 +2514,6 @@ sysctl_set (NMPlatform *platform, const char *path, const char *value)
                       path, value);
        }
 
-       g_free (actual);
        close (fd);
        return (nwrote == len);
 }
-- 
2.5.0