Re: [Qemu-devel] [PATCH 3/3] qga: set file descriptor in qmp_guest_file_open non-blocking on Win32

[Michael Roth <mdroth@linux.vnet.ibm.com>]

Quoting Denis V. Lunev (2015-10-27 12:48:43)
> From: Olga Krishtal <okrishtal@parallels.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.
> 
> The patch introduces analog of qemu_set_non/block for HANDLES.
> The usage of handles in qemu_set_non/block is impossible, because for
> win32 there is a difference between file discriptors and file handles,
> and all file ops are made via Win32 api.

If this is specific to HANDLEs, why do we need to cast back and forth
between int64_t and HANDLE? I haven't build tested, but it seems like
this would break for 32-bit mingw builds.

I would define these as qemu_set_*_by_handle(HANDLE fh, ...) instead
and make them win32 only. If someone wants to introduce a FILE*
variant for posix they can introduce it as
qemu_set_*_by_handle(FILE *fh, ...) rather than us needing to
abstract away the handle type.

> 
> Signed-off-by: Olga Krishtal <okrishtal@parallels.com>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Michael Roth <mdroth@linux.vnet.ibm.com>
> CC: Stefan Weil <sw@weilnetz.de>
> ---
>  include/qemu/sockets.h |  2 ++
>  qga/commands-win32.c   |  6 ++++++
>  util/oslib-win32.c     | 41 +++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 49 insertions(+)
> 
> diff --git a/include/qemu/sockets.h b/include/qemu/sockets.h
> index 5a183c5..e2323f4 100644
> --- a/include/qemu/sockets.h
> +++ b/include/qemu/sockets.h
> @@ -39,6 +39,8 @@ int socket_set_cork(int fd, int v);
>  int socket_set_nodelay(int fd);
>  void qemu_set_block(int fd);
>  void qemu_set_nonblock(int fd);
> +void qemu_set_nonblock_by_handle(int64_t fh);
> +void qemu_set_block_by_handle(int64_t fh);
>  int socket_set_fast_reuse(int fd);
>  int send_all(int fd, const void *buf, int len1);
>  int recv_all(int fd, void *buf, int len1, bool single_read);
> diff --git a/qga/commands-win32.c b/qga/commands-win32.c
> index 97f19d5..f959d75 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
> @@ -158,6 +159,11 @@ 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_by_handle((int64_t)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 09f9e98..4a9fd8e 100644
> --- a/util/oslib-win32.c
> +++ b/util/oslib-win32.c
> @@ -121,6 +121,37 @@ struct tm *localtime_r(const time_t *timep, struct tm *result)
>  }
>  #endif /* CONFIG_LOCALTIME_R */
> 
> +static void qemu_set_handle_nonblocking(int64_t fh, bool nonblocking)
> +{
> +    DWORD file_type, pipe_state;
> +    HANDLE handle = (HANDLE)fh;
> +    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)) {
> +        return;
> +    }
> +    /* 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);
> +}
> +
>  void qemu_set_block(int fd)
>  {
>      unsigned long opt = 0;
> @@ -135,6 +166,16 @@ void qemu_set_nonblock(int fd)
>      qemu_fd_register(fd);
>  }
> 
> +void qemu_set_block_by_handle(int64_t fh)
> +{
> +    qemu_set_handle_nonblocking(fh, false);
> +}
> +
> +void qemu_set_nonblock_by_handle(int64_t fh)
> +{
> +    qemu_set_handle_nonblocking(fh, true);
> +}
> +
>  int socket_set_fast_reuse(int fd)
>  {
>      /* Enabling the reuse of an endpoint that was used by a socket still in
> -- 
> 2.1.4
>