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

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

Quoting Denis V. Lunev (2015-10-07 05:59:34)
> 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.
> 
> 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   | 52 +++++++++++++++++++++++++++++++++++++++++++++++-----
>  2 files changed, 53 insertions(+), 5 deletions(-)
> 
> diff --git a/qga/commands-win32.c b/qga/commands-win32.c
> index 3374678..3274417 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(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..f19aed5 100644
> --- a/util/oslib-win32.c
> +++ b/util/oslib-win32.c
> @@ -121,17 +121,59 @@ 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;
> +
> +    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 */
> +    unsigned long opt = (unsigned long)nonblocking;
> +    if (!nonblocking) {
> +        WSAEventSelect(fd, NULL, 0);
> +    }
>      ioctlsocket(fd, FIONBIO, &opt);
>  }
> 
> +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_set_fd_nonblocking(fd, true);
>      qemu_fd_register(fd);

This still potentially calls qemu_fd_register() on a non-socket FD as
noted in prior review. I think the fix is trivial, but if you can
change and re-test that would be ideal.

Since guest-file* already supports reading/writing to w32 pipes I can
pick this up during soft-freeze if it comes to that.

Since we're still taking the approach of generalizing
qemu_set_nonblock() for win32 I'd really prefer to get Stefan's
Ack/Reviewed-by before applying.

>  }
> 
> -- 
> 2.1.4
>