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

["Denis V. Lunev" <den@openvz.org>]

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 <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 */
> ... 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
>