build: suppress an ignored-dup-return-value warning

[libguestfs.git] / src / guestfs.c

diff --git a/src/guestfs.c b/src/guestfs.c
index 37869e8..1cd4f9e 100644 (file)
--- a/src/guestfs.c
+++ b/src/guestfs.c
@@ -59,6 +59,7 @@
 
 #include "guestfs.h"
 #include "guestfs_protocol.h"
+#include "ignore-value.h"
 
 #ifdef HAVE_GETTEXT
 #include "gettext.h"
@@ -799,14 +800,31 @@ guestfs_add_drive (guestfs_h *g, const char *filename)
     return -1;
   }
 
-  if (access (filename, F_OK) == -1) {
-    perrorf (g, "%s", filename);
-    return -1;
+  /* cache=off improves reliability in the event of a host crash.
+   *
+   * However this option causes qemu to try to open the file with
+   * O_DIRECT.  This fails on some filesystem types (notably tmpfs).
+   * So we check if we can open the file with or without O_DIRECT,
+   * and use cache=off (or not) accordingly.
+   *
+   * This test also checks for the presence of the file, which
+   * is a documented semantic of this interface.
+   */
+  int fd = open (filename, O_RDONLY|O_DIRECT);
+  if (fd >= 0) {
+    close (fd);
+    snprintf (buf, len, "file=%s,cache=off,if=" DRIVE_IF, filename);
+  } else {
+    fd = open (filename, O_RDONLY);
+    if (fd >= 0) {
+      close (fd);
+      snprintf (buf, len, "file=%s,if=" DRIVE_IF, filename);
+    } else {
+      perrorf (g, "%s", filename);
+      return -1;
+    }
   }
 
-  /* cache=off improves reliability in the event of a host crash. */
-  snprintf (buf, len, "file=%s,cache=off,if=%s", filename, DRIVE_IF);
-
   return guestfs_config (g, "-drive", buf);
 }
 
@@ -1144,11 +1162,18 @@ guestfs_launch (guestfs_h *g)
     close (1);
     close (wfd[1]);
     close (rfd[0]);
-    dup (wfd[0]);
-    dup (rfd[1]);
+
+    int fail = 0;
+    fail |= dup (wfd[0]);
+    fail |= dup (rfd[1]);
     close (wfd[0]);
     close (rfd[1]);
 
+    if (fail) {
+      perror ("dup failed");
+      _exit (1);
+    }
+
 #if 0
     /* Set up a new process group, so we can signal this process
      * and all subprocesses (eg. if qemu is really a shell script).
@@ -1680,7 +1705,7 @@ stdout_event (struct guestfs_main_loop *ml, guestfs_h *g, void *data,
 
   /* In verbose mode, copy all log messages to stderr. */
   if (g->verbose)
-    write (2, buf, n);
+    ignore_value (write (STDERR_FILENO, buf, n));
 
   /* It's an actual log message, send it upwards if anyone is listening. */
   if (g->log_message_cb)