[Qemu-devel] [PATCH v2 0/2] qga: non-blocking fd cleanups

[Qemu-devel] [PATCH v2 0/2] qga: non-blocking fd cleanups

[Denis V. Lunev]

This patchset is reincarnation of one patch discussed in the scope of
QEMU 2.4 and rejected for that time. Actually we should use
non-blocking descriptors in QGA on Windows in guest-file-open exactly
like was done for Posix.

Changes from v1:
- call to qemu_fd_register is moved to a proper place
- moved declaration of opt to a proper place

Signed-off-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: Olga Krishtal <okrishtal@virtuozzo.com>
Reviewed-by: Yuri Pudgorodskiy <yur@virtuozzo.com>
CC: Michael Roth <mdroth@linux.vnet.ibm.com>

[Qemu-devel] [PATCH 1/2] qga: drop hand-made guest_file_toggle_flags helper

[Denis V. Lunev]

We'd better use generic qemu_set_nonblock directly.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Yuri Pudgorodskiy <yur@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
CC: Michael Roth <mdroth@linux.vnet.ibm.com>
---
 qga/commands-posix.c | 27 ++-------------------------
 1 file changed, 2 insertions(+), 25 deletions(-)

diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index b03c316..43d1ed4 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -28,6 +28,7 @@
 #include "qapi/qmp/qerror.h"
 #include "qemu/queue.h"
 #include "qemu/host-utils.h"
+#include "qemu/sockets.h"
 
 #ifndef CONFIG_HAS_ENVIRON
 #ifdef __APPLE__
@@ -383,27 +384,6 @@ safe_open_or_create(const char *path, const char *mode, Error **errp)
     return NULL;
 }
 
-static int guest_file_toggle_flags(int fd, int flags, bool set, Error **err)
-{
-    int ret, old_flags;
-
-    old_flags = fcntl(fd, F_GETFL);
-    if (old_flags == -1) {
-        error_setg_errno(err, errno, QERR_QGA_COMMAND_FAILED,
-                         "failed to fetch filehandle flags");
-        return -1;
-    }
-
-    ret = fcntl(fd, F_SETFL, set ? (old_flags | flags) : (old_flags & ~flags));
-    if (ret == -1) {
-        error_setg_errno(err, errno, QERR_QGA_COMMAND_FAILED,
-                         "failed to set filehandle flags");
-        return -1;
-    }
-
-    return ret;
-}
-
 int64_t qmp_guest_file_open(const char *path, bool has_mode, const char *mode,
                             Error **errp)
 {
@@ -424,10 +404,7 @@ int64_t qmp_guest_file_open(const char *path, bool has_mode, const char *mode,
     /* set fd non-blocking to avoid common use cases (like reading from a
      * named pipe) from hanging the agent
      */
-    if (guest_file_toggle_flags(fileno(fh), O_NONBLOCK, true, errp) < 0) {
-        fclose(fh);
-        return -1;
-    }
+    qemu_set_nonblock(fileno(fh));
 
     handle = guest_file_handle_add(fh, errp);
     if (handle < 0) {
-- 
2.1.4

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

[Denis V. Lunev]

From: Olga Krishtal <okrishtal@virtuozzo.com>

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 <okrishtal@virtuozzo.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Yuri Pudgorodskiy <yur@virtuozzo.com>
CC: Michael Roth <mdroth@linux.vnet.ibm.com>
CC: Stefan Weil <sw@weilnetz.de>
---
 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

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

[Michael Roth]

Quoting Denis V. Lunev (2015-10-15 07:51:11)
> From: Olga Krishtal <okrishtal@virtuozzo.com>
> 
> 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 <okrishtal@virtuozzo.com>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> Reviewed-by: Yuri Pudgorodskiy <yur@virtuozzo.com>
> CC: Michael Roth <mdroth@linux.vnet.ibm.com>
> CC: Stefan Weil <sw@weilnetz.de>
> ---
>  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));

This doesn't seem to build for me:

  CC    qga/channel-win32.o
  /home/mdroth/w/qemu3.git/qga/commands-win32.c: In function
  ‘qmp_guest_file_open’:
  /home/mdroth/w/qemu3.git/qga/commands-win32.c:165: warning:
  dereferencing ‘void *’ pointer
  /home/mdroth/w/qemu3.git/qga/commands-win32.c:165: error: request for
  member ‘_file’ in something not a structure or union

That's with ubuntu 14.04 and running:

  ../qemu3.git/configure --cross-prefix=i586-mingw32msvc-
  --target-list=x86_64-softmmu --extra-cflags=-Wall && make -j4

fileno() expects a FILE *, but fh is actually a HANDLE. Is there an
environment where this is not the case? I think what you want is
_open_osfhandle().

Note that it looks like you then might need to track the resulting fd and
use _close() in place of CloseHandle() in guest-file-close:

  https://msdn.microsoft.com/en-us/library/bdts1c9x.aspx

That also make me a bit concerned that read/write operations on the
HANDLE would then need to be replaced with read()/write() etc... the
documentation doesn't seem very clear on this.

I'm starting to think it best we just introduce a
qemu_set_nonblock_w32_handle(HANDLE ...) to do this, and leave the
existing qemu_set_nonblock() as it was before (winsock FDs only).

If people want to risk whatever wierd stuff might come about by
switching between HANDLE/fd they can use
_open_osfhandle()/_get_osfhandle() prior to calling
qemu_set_nonblock*(). But since we started off with a HANDLE in the
first place, there's no reason to us to switch to fd, then back to
HANDLE.

> +
>      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
>