Re: [PATCH 4/5] util/qemu-sockets: Enable unix socket support on Windows

[Bin Meng]

On Wed, Jul 27, 2022 at 4:53 PM Konstantin Kostiuk <kkostiuk@redhat.com> wrote:
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> On Wed, Jul 27, 2022 at 10:47 AM Bin Meng <bmeng.cn@gmail.com> wrote:
>>
>> From: Bin Meng <bin.meng@windriver.com>
>>
>> Support for the unix socket has existed both in BSD and Linux for the
>> longest time, but not on Windows. Since Windows 10 build 17063 [1],
>> the native support for the unix socket has came to Windows. Starting
>> this build, two Win32 processes can use the AF_UNIX address family
>> over Winsock API to communicate with each other.
>>
>> Introduce a new build time config option CONFIG_AF_UNIX when the build
>> host has such a capability, and a run-time check afunix_available() for
>> Windows host in the QEMU sockets util codes.
>>
>> [1] https://devblogs.microsoft.com/commandline/af_unix-comes-to-windows/
>>
>> Signed-off-by: Xuzhou Cheng <xuzhou.cheng@windriver.com>
>> Signed-off-by: Bin Meng <bin.meng@windriver.com>
>> ---
>>
>>  meson.build         |  6 ++++++
>>  util/qemu-sockets.c | 48 ++++++++++++++++++++++++++++++++++++++-------
>>  2 files changed, 47 insertions(+), 7 deletions(-)
>>
>> diff --git a/meson.build b/meson.build
>> index 75aaca8462..73e5de5957 100644
>> --- a/meson.build
>> +++ b/meson.build
>> @@ -2327,6 +2327,12 @@ have_afalg = get_option('crypto_afalg') \
>>    '''), error_message: 'AF_ALG requested but could not be 
>> detected').allowed()
>>  config_host_data.set('CONFIG_AF_ALG', have_afalg)
>>
>> +if targetos != 'windows'
>> +  config_host_data.set('CONFIG_AF_UNIX', true)
>> +else
>> +  config_host_data.set('CONFIG_AF_UNIX', cc.has_header('afunix.h'))
>> +endif
>> +
>>  config_host_data.set('CONFIG_AF_VSOCK', cc.has_header_symbol(
>>    'linux/vm_sockets.h', 'AF_VSOCK',
>>    prefix: '#include <sys/socket.h>',
>> diff --git a/util/qemu-sockets.c b/util/qemu-sockets.c
>> index 0e2298278f..d85f3ea3ee 100644
>> --- a/util/qemu-sockets.c
>> +++ b/util/qemu-sockets.c
>> @@ -17,6 +17,15 @@
>>   */
>>  #include "qemu/osdep.h"
>>
>> +#if defined(CONFIG_WIN32) && defined(CONFIG_AF_UNIX)
>> +# include <afunix.h>
>> +/*
>> + * AF_UNIX support is available since Windows 10 build 17063
>> + * See https://devblogs.microsoft.com/commandline/af_unix-comes-to-windows/
>> + */
>> +# define WIN_BUILD_AF_UNIX 17063
>> +#endif /* CONFIG_WIN32 && CONFIG_AF_UNIX */
>> +
>>  #ifdef CONFIG_AF_VSOCK
>>  #include <linux/vm_sockets.h>
>>  #endif /* CONFIG_AF_VSOCK */
>> @@ -880,7 +889,7 @@ static int vsock_parse(VsockSocketAddress *addr, const 
>> char *str,
>>  }
>>  #endif /* CONFIG_AF_VSOCK */
>>
>> -#ifndef _WIN32
>> +#ifdef CONFIG_AF_UNIX
>>
>>  static bool saddr_is_abstract(UnixSocketAddress *saddr)
>>  {
>> @@ -900,6 +909,17 @@ static bool saddr_is_tight(UnixSocketAddress *saddr)
>>  #endif
>>  }
>>
>> +#ifdef CONFIG_WIN32
>> +static bool afunix_available(void)
>> +{
>> +    OSVERSIONINFOEXW os_version = { 0 };
>> +
>> +    os_get_win_version(&os_version);
>> +
>> +    return os_version.dwBuildNumber >= WIN_BUILD_AF_UNIX;
>
>
> I think this is a bad variant to check feature support by checking
> Windows build. From my point, you should try to create an AF_UNIX
> socket and if it fails then fall back to the old behavior.
>

The caller intends to create an AF_UNIX socket, and if Windows does
not have the capability, it fails, and we return -1 to the caller.
I am not sure what old behavior we should fall back to.

Regards,
Bin