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 Michael Roth (2015-10-27 14:11:12)
> 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.

Actually that would be silly since win32 has FILE as well. So I think
this interface will only ever make sense for HANDLE so let's be
explicit about it.

> 
> > 
> > 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
> >