[PATCH 3 of 9] tools/xc: rework xc_save.c:switch_qemu_logdirty

[Olaf Hering <olaf@aepfle.de>]

# HG changeset patch
# User Olaf Hering <olaf@aepfle.de>
# Date 1364481337 -3600
# Node ID 99d809a358d9748d97044cc5721a028cffbcf5fe
# Parent  2b4e40439417fa09c3a6a49565a161c6dc4ddc15
tools/xc: rework xc_save.c:switch_qemu_logdirty

Rework code in switch_qemu_logdirty, fix also memleak.

v2:
 - use DPRINTF to print watchpoint result

Signed-off-by: Olaf Hering <olaf@aepfle.de>

diff -r 2b4e40439417 -r 99d809a358d9 tools/xcutils/xc_save.c
--- a/tools/xcutils/xc_save.c
+++ b/tools/xcutils/xc_save.c
@@ -7,6 +7,7 @@
  *
  */
 
+#define _GNU_SOURCE
 #include <unistd.h>
 #include <err.h>
 #include <stdlib.h>
@@ -109,8 +110,10 @@ static int switch_qemu_logdirty(int domi
 {
     xc_interface *xch = si.xch;
     struct xs_handle *xs;
-    char *path, *p, *ret_str, *cmd_str, **watch;
+    char *path, *dir_p, *ret_str, **watch;
+    const char *cmd_str;
     unsigned int len;
+    int ret, again;
     struct timeval tv;
     fd_set fdset;
 
@@ -118,65 +121,56 @@ static int switch_qemu_logdirty(int domi
         PERROR("Couldn't contact xenstore");
         exit(1);
     }
-    if (!(path = strdup("/local/domain/0/device-model/"))) {
-        PERROR("can't get domain path in store");
+
+    ret = asprintf(&path, "/local/domain/0/device-model/%i/logdirty/ret", domid);
+    if (ret < 0) {
+        ERROR("Couldn't construct xenstore path");
         exit(1);
     }
-    if (!(path = realloc(path, strlen(path) 
-                         + 10 
-                         + strlen("/logdirty/cmd") + 1))) {
-        PERROR("no memory for constructing xenstore path");
-        exit(1);
-    }
-    snprintf(path + strlen(path), 11, "%i", domid);
-    strcat(path, "/logdirty/");
-    p = path + strlen(path);
-
+    /* Pointer to directory */
+    dir_p = path + ret - 3;
 
     /* Watch for qemu's return value */
-    strcpy(p, "ret");
-    if (!xs_watch(xs, path, "qemu-logdirty-ret"))
-    {
-        ERROR("can't set watch in store (%s)\n", path);
+    if (!xs_watch(xs, path, "qemu-logdirty-ret")) {
+        PERROR("can't set watch in store (%s)", path);
         exit(1);
     }
 
-    if (!(cmd_str = strdup( enable == 0 ? "disable" : "enable"))) {
-        PERROR("can't get logdirty cmd path in store");
+    cmd_str = enable ? "enable" : "disable";
+
+    /* Tell qemu that we want it to start logging dirty pages to Xen */
+    strcpy(dir_p, "cmd");
+    if (!xs_write(xs, XBT_NULL, path, cmd_str, strlen(cmd_str))) {
+        PERROR("can't write to store path (%s)", path);
         exit(1);
     }
 
-    /* Tell qemu that we want it to start logging dirty page to Xen */
-    strcpy(p, "cmd");
-    if (!xs_write(xs, XBT_NULL, path, cmd_str, strlen(cmd_str))) {
-        PERROR("can't write  to store path (%s)\n", path);
-        exit(1);
-    }
+    /* Restore initial path */
+    strcpy(dir_p, "ret");
+    /* Wait a while for qemu to signal that it has serviced logdirty command */
+    do {
+        tv.tv_sec = 5;
+        tv.tv_usec = 0;
+        FD_ZERO(&fdset);
+        FD_SET(xs_fileno(xs), &fdset);
+        errno = 0;
 
-    /* Wait a while for qemu to signal that it has service logdirty command */
- read_again:
-    tv.tv_sec = 5;
-    tv.tv_usec = 0;
-    FD_ZERO(&fdset);
-    FD_SET(xs_fileno(xs), &fdset);
-
-    if ((select(xs_fileno(xs) + 1, &fdset, NULL, NULL, &tv)) != 1) {
-        PERROR("timed out waiting for qemu logdirty response.\n");
-        exit(1);
-    }
-
-    watch = xs_read_watch(xs, &len);
-    free(watch);
-
-    strcpy(p, "ret");
-    ret_str = xs_read(xs, XBT_NULL, path, &len);
-    if (ret_str == NULL || strcmp(ret_str, cmd_str))
+        if ((select(xs_fileno(xs) + 1, &fdset, NULL, NULL, &tv)) != 1) {
+            PERROR("timed out waiting for qemu logdirty response.");
+            exit(1);
+        }
+    
+        watch = xs_read_watch(xs, &len);
+        free(watch);
+    
+        ret_str = xs_read(xs, XBT_NULL, path, &len);
+        again = ret_str == NULL || strcmp(ret_str, cmd_str);
+        DPRINTF("Got '%s' from logdirty%s.\n", ret_str, again ? ", retrying" : "");
+        free(ret_str);
         /* Watch fired but value is not yet right */
-        goto read_again;
+    } while (again);
 
     free(path);
-    free(cmd_str);
-    free(ret_str);
 
     return 0;
 }