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

[Stefan Weil]

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.

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

pipe_state could be declared here.

>> +        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.

>> +    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.

> 
> 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