[PATCH v3 1/2] util: Introduce qemu_get_host_name()

[Michal Privoznik]

This function offers operating system agnostic way to fetch host
name. It is implemented for both POSIX-like and Windows systems.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
---
 include/qemu/osdep.h | 10 ++++++++++
 util/oslib-posix.c   | 35 +++++++++++++++++++++++++++++++++++
 util/oslib-win32.c   | 13 +++++++++++++
 3 files changed, 58 insertions(+)

diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index ff7c17b857..a795d46b28 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -607,4 +607,14 @@ static inline void qemu_reset_optind(void)
 #endif
 }
 
+/**
+ * qemu_get_host_name:
+ * @errp: Error object
+ *
+ * Operating system agnostic way of querying host name.
+ *
+ * Returns allocated hostname (caller should free), NULL on failure.
+ */
+char *qemu_get_host_name(Error **errp);
+
 #endif
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index 916f1be224..3997ee0442 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -761,3 +761,38 @@ void sigaction_invoke(struct sigaction *action,
     }
     action->sa_sigaction(info->ssi_signo, &si, NULL);
 }
+
+#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
+
+char *qemu_get_host_name(Error **errp)
+{
+    long len = -1;
+    g_autofree char *hostname = NULL;
+
+#ifdef _SC_HOST_NAME_MAX
+    len = sysconf(_SC_HOST_NAME_MAX);
+#endif /* _SC_HOST_NAME_MAX */
+
+    if (len < 0) {
+        len = HOST_NAME_MAX;
+    }
+
+    /* Unfortunately, gethostname() below does not guarantee a
+     * NULL terminated string. Therefore, allocate one byte more
+     * to be sure. */
+    hostname = g_new0(char, len + 1);
+
+    if (gethostname(hostname, len) < 0) {
+        error_setg_errno(errp, errno,
+                         "cannot get hostname");
+        return NULL;
+    }
+
+    return g_steal_pointer(&hostname);
+}
diff --git a/util/oslib-win32.c b/util/oslib-win32.c
index e9b14ab178..3b49d27297 100644
--- a/util/oslib-win32.c
+++ b/util/oslib-win32.c
@@ -808,3 +808,16 @@ bool qemu_write_pidfile(const char *filename, Error **errp)
     }
     return true;
 }
+
+char *qemu_get_host_name(Error **errp)
+{
+    wchar_t tmp[MAX_COMPUTERNAME_LENGTH + 1];
+    DWORD size = G_N_ELEMENTS(tmp);
+
+    if (GetComputerNameW(tmp, &size) == 0) {
+        error_setg_win32(errp, GetLastError(), "failed close handle");
+        return NULL;
+    }
+
+    return g_utf16_to_utf8(tmp, size, NULL, NULL, NULL);
+}
-- 
2.26.2