[Qemu-devel] [PATCH 2/2] qga: set file descriptors in qmp_guest_file_open non-blocking on Win32

[Denis V. Lunev]

From: Olga Krishtal <address@hidden>

Set fd non-blocking to avoid common use cases (like reading from a
named pipe) from hanging the agent. This was missed in the original
code.

Restore compatibility with Posix implementation.

The patch adds Win32 specific implementation of qemu_set_nonblock.

On Windows OS there is a separate API for changing flags of file, pipes
and sockets. Portable way to change file descriptor flags requires
to detect file descriptor type and proper actions depending of that
type. The patch adds wrapper qemu_set_fd_nonblocking into Windows specific
code to handle this stuff properly.

The only problem is that qemu_set_nonblock is void but this should not
be a big deal.

Despite the fact that qemu_fd_register() is used only once here and now
it is difficult to drop this function as it uses AioContext internals
which we do not want to involve here.

Signed-off-by: Olga Krishtal <address@hidden>
Signed-off-by: Denis V. Lunev <address@hidden>
Reviewed-by: Yuri Pudgorodskiy <address@hidden>
CC: Michael Roth <address@hidden>
CC: Stefan Weil <address@hidden>
---
 qga/commands-win32.c |  6 ++++++
 util/oslib-win32.c   | 57 ++++++++++++++++++++++++++++++++++++++++++++++------
 2 files changed, 57 insertions(+), 6 deletions(-)

diff --git a/qga/commands-win32.c b/qga/commands-win32.c
index 41bdd3f..745bddf 100644
--- a/qga/commands-win32.c
+++ b/qga/commands-win32.c
@@ -34,6 +34,7 @@
 #include "qapi/qmp/qerror.h"
 #include "qemu/queue.h"
 #include "qemu/host-utils.h"
+#include "qemu/sockets.h"
 
 #ifndef SHTDN_REASON_FLAG_PLANNED
 #define SHTDN_REASON_FLAG_PLANNED 0x80000000
@@ -156,6 +157,11 @@ int64_t qmp_guest_file_open(const char *path, bool 
has_mode,
         return -1;
     }
 
+    /* set fd non-blocking to avoid common use cases (like reading from a
+     * named pipe) from hanging the agent
+     */
+    qemu_set_nonblock(fileno(fh));
+
     fd = guest_file_handle_add(fh, errp);
     if (fd < 0) {
         CloseHandle(&fh);
diff --git a/util/oslib-win32.c b/util/oslib-win32.c
index 08f5a9c..e1580c8 100644
--- a/util/oslib-win32.c
+++ b/util/oslib-win32.c
@@ -121,18 +121,63 @@ struct tm *localtime_r(const time_t *timep, struct tm 
*result)
 }
 #endif /* CONFIG_LOCALTIME_R */
 
-void qemu_set_block(int fd)
+static void qemu_set_fd_nonblocking(int fd, bool nonblocking)
 {
-    unsigned long opt = 0;
-    WSAEventSelect(fd, NULL, 0);
+    HANDLE handle;
+    DWORD file_type, pipe_state;
+    unsigned long opt = (unsigned long)nonblocking;
+
+    handle = (HANDLE)_get_osfhandle(fd);
+    if (handle == INVALID_HANDLE_VALUE) {
+        return;
+    }
+
+    file_type = GetFileType(handle);
+    if (file_type != FILE_TYPE_PIPE) {
+        return;
+    }
+
+    /* If file_type == FILE_TYPE_PIPE, according to msdn
+     * the specified file is socket or named pipe */
+    if (GetNamedPipeHandleState(handle, &pipe_state, NULL,
+                                NULL, NULL, NULL, 0)) {
+        /* The fd is named pipe fd */
+        if (!nonblocking == !(pipe_state & PIPE_NOWAIT)) {
+            /* In this case we do not need perform any operation, because
+             * nonblocking = true and PIPE_NOWAIT is already set or
+             * nonblocking = false and PIPE_NOWAIT is not set */
+            return;
+        }
+
+        if (nonblocking) {
+            pipe_state |= PIPE_NOWAIT;
+        } else {
+            pipe_state &= ~PIPE_NOWAIT;
+        }
+
+        SetNamedPipeHandleState(handle, &pipe_state, NULL, NULL);
+        return;
+    }
+
+    /* The fd is socket fd */
+    if (!nonblocking) {
+        WSAEventSelect(fd, NULL, 0);
+    }
     ioctlsocket(fd, FIONBIO, &opt);
+    if (nonblocking) {
+        qemu_fd_register(fd);
+    }
+    return;
+}
+
+void qemu_set_block(int fd)
+{
+    qemu_set_fd_nonblocking(fd, false);
 }
 
 void qemu_set_nonblock(int fd)
 {
-    unsigned long opt = 1;
-    ioctlsocket(fd, FIONBIO, &opt);
-    qemu_fd_register(fd);
+    qemu_set_fd_nonblocking(fd, true);
 }
 
 int socket_set_fast_reuse(int fd)
-- 
2.1.4