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

[Denis V. Lunev]

On 10/12/2015 09:39 PM, Stefan Weil wrote:
> Hi,
>
> please see my inline comments below.
>
> Am 12.10.2015 um 19:38 schrieb Michael Roth:
> > Quoting Denis V. Lunev (2015-10-07 05:59:34)
> > > 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.
> > >
> > > 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   | 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 */
> ... or an anonymous pipe.
ok

> > > +    if (GetNamedPipeHandleState(handle, &pipe_state, NULL,
> > > +                                NULL, NULL, NULL, 0)) {
> > > +        /* The fd is named pipe fd */
> pipe_state could be declared here.

not ok. pipe_state is initialized in GetNamedPipeHandleState above,
which is in the main scope of the function


> > > +        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;
> The QEMU style still requires variable declarations at the beginning of
> a code block.
ok

> > > +    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.
> Yes.
sure :) already discussed


> > 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.
> >
> > >   }
> I'm sorry that I cannot run any tests, but as far as I can see,
> the code will be fine if all the notes are taken into account.
>
> Regards
> Stefan