Re: [PATCH] qga: Use gethostname() instead of g_get_host_name()

[Marc-André Lureau]

Hi

On Tue, Jun 16, 2020 at 12:35 PM Michal Privoznik <mprivozn@redhat.com> wrote:

Problem with g_get_host_name() is that on the first call it saves
the hostname into a global variable and from then on, every
subsequent call returns the saved hostname. Even if the hostname
changes. This doesn't play nicely with guest agent, because if
the hostname is acquired before the guest is set up (e.g. on the
first boot, or before DHCP) we will report old, invalid hostname.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1845127

lgtm,

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>

(fwiw, I opened a glib issue: https://gitlab.gnome.org/GNOME/glib/-/issues/2130)

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
---
 qga/commands.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 52 insertions(+), 4 deletions(-)

diff --git a/qga/commands.c b/qga/commands.c
index efc8b90281..ce3c2041a6 100644
--- a/qga/commands.c
+++ b/qga/commands.c
@@ -512,14 +512,62 @@ int ga_parse_whence(GuestFileWhence *whence, Error **errp)
     return -1;
 }

+#ifndef HOST_NAME_MAX
+# ifdef _POSIX_HOST_NAME_MAX
+#  define HOST_NAME_MAX _POSIX_HOST_NAME_MAX
+# else
+#  define HOST_NAME_MAX 255
+# endif
+#endif
+
 GuestHostName *qmp_guest_get_host_name(Error **errp)
 {
     GuestHostName *result = NULL;
-    gchar const *hostname = g_get_host_name();
-    if (hostname != NULL) {
-        result = g_new0(GuestHostName, 1);
-        result->host_name = g_strdup(hostname);
+    g_autofree char *hostname = NULL;
+
+    /*
+     * We want to avoid using g_get_host_name() because that
+     * caches the result and we wouldn't reflect changes in the
+     * host name.
+     */
+
+#ifndef G_OS_WIN32
+    long len = -1;
+
+#ifdef _SC_HOST_NAME_MAX
+    len = sysconf(_SC_HOST_NAME_MAX);
+#endif /* _SC_HOST_NAME_MAX */
+
+    if (len < 0) {
+        len = HOST_NAME_MAX;
     }
+
+    hostname = g_malloc0(len + 1);
+
+    if (gethostname(hostname, len) < 0) {
+        return NULL;
+    }
+
+#else /* G_OS_WIN32 */
+
+    wchar_t tmp[MAX_COMPUTERNAME_LENGTH + 1];
+    DWORD size = G_N_ELEMENTS(tmp);
+
+    if (GetComputerNameW(tmp, &size) != 0) {
+        /*
+         * Indeed, on Windows retval of zero means failure
+         * and nonzero means success.
+         */
+        hostname = g_utf16_to_utf8(tmp, size, NULL, NULL, NULL);
+    }
+#endif /* G_OS_WIN32 */
+
+    if (!hostname) {
+        hostname = g_strdup("localhost");
+    }
+
+    result = g_new0(GuestHostName, 1);
+    result->host_name = g_steal_pointer(&hostname);
     return result;
 }

--
2.26.2

--

Marc-André Lureau