[PATCH] registry: Make RegisterExtensionNames slightly less inefficient (v2)

[Adam Jackson]

v2: zero the buffer before reading into it to protect against malformed
input file [aaronp]

The big change is to defer strdup until we actually know the line
matches the extension we're initializing.  This cuts the number of calls
to strdup on this path from 24090 to 554, and 'Xvfb -pogo' drops from
about 45M to 38M instructions retired according to valgrind.

Signed-off-by: Adam Jackson <ajax at redhat.com>
---
 dix/registry.c | 30 +++++++++++++++---------------
 1 file changed, 15 insertions(+), 15 deletions(-)

diff --git a/dix/registry.c b/dix/registry.c
index 82a3340..3880824 100644
--- a/dix/registry.c
+++ b/dix/registry.c
@@ -124,13 +124,17 @@ RegisterExtensionNames(ExtensionEntry * extEntry)
 {
     char buf[256], *lineobj, *ptr;
     unsigned offset;
+    int namelen;
 
     if (fh == NULL)
         return;
 
+    namelen = strlen(extEntry->name);
+
     rewind(fh);
 
-    while (fgets(buf, sizeof(buf), fh)) {
+    /* clear the buffer before fgets'ing into it */
+    while (memset(buf, 0, sizeof (buf)), fgets(buf, sizeof(buf), fh)) {
         lineobj = NULL;
         ptr = strchr(buf, '\n');
         if (ptr)
@@ -149,26 +153,22 @@ RegisterExtensionNames(ExtensionEntry * extEntry)
             goto invalid;
         }
 
-        /* Check for space character in the fifth position */
-        ptr = strchr(buf, ' ');
-        if (!ptr || ptr != buf + 4)
+        /* check for proper formatting */
+        if (buf[4] != ' ')
             goto invalid;
 
+        /* check for extension name match */
+        if (strncmp(buf + 5, extEntry->name, namelen))
+            goto skip;
+
+        if (buf[5 + namelen] != ':')
+            goto skip;
+
         /* Duplicate the string after the space */
-        lineobj = strdup(ptr + 1);
+        lineobj = strdup(buf + 5);
         if (!lineobj)
             continue;
 
-        /* Check for a colon somewhere on the line */
-        ptr = strchr(buf, ':');
-        if (!ptr)
-            goto invalid;
-
-        /* Compare the part before colon with the target extension name */
-        *ptr = 0;
-        if (strcmp(buf + 5, extEntry->name))
-            goto skip;
-
         /* Get the opcode for the request, event, or error */
         offset = strtol(buf + 1, &ptr, 10);
         if (offset == 0 && ptr == buf + 1)
-- 
1.8.4.2