Re: [PATCH v4 04/11] osdep: implement qemu_socketpair() for win32

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Mar 08, 2023 at 10:53:13AM +0400, Marc-André Lureau wrote:
> Hi
> 
> On Tue, Mar 7, 2023 at 6:50 PM Daniel P. Berrangé <berrange@redhat.com> wrote:
> >
> > On Mon, Mar 06, 2023 at 04:27:44PM +0400, marcandre.lureau@redhat.com wrote:
> > > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> > >
> > > Manually implement a socketpair() function, using UNIX sockets and
> > > simple peer credential checking.
> > >
> > > QEMU doesn't make much use of socketpair, beside vhost-user which is not
> > > available for win32 at this point. However, I intend to use it for
> > > writing some new portable tests.
> > >
> > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > ---
> > >  include/qemu/sockets.h |   2 -
> > >  util/oslib-win32.c     | 110 +++++++++++++++++++++++++++++++++++++++++
> > >  2 files changed, 110 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/include/qemu/sockets.h b/include/qemu/sockets.h
> > > index 2b0698a7c9..d935fd80da 100644
> > > --- a/include/qemu/sockets.h
> > > +++ b/include/qemu/sockets.h
> > > @@ -15,7 +15,6 @@ int inet_aton(const char *cp, struct in_addr *ia);
> > >  bool fd_is_socket(int fd);
> > >  int qemu_socket(int domain, int type, int protocol);
> > >
> > > -#ifndef WIN32
> > >  /**
> > >   * qemu_socketpair:
> > >   * @domain: specifies a communication domain, such as PF_UNIX
> > > @@ -30,7 +29,6 @@ int qemu_socket(int domain, int type, int protocol);
> > >   * Return 0 on success.
> > >   */
> > >  int qemu_socketpair(int domain, int type, int protocol, int sv[2]);
> > > -#endif
> > >
> > >  int qemu_accept(int s, struct sockaddr *addr, socklen_t *addrlen);
> > >  /*
> > > diff --git a/util/oslib-win32.c b/util/oslib-win32.c
> > > index 29a667ae3d..16f8a67f7e 100644
> > > --- a/util/oslib-win32.c
> > > +++ b/util/oslib-win32.c
> > > @@ -310,6 +310,116 @@ bool qemu_socket_unselect(int sockfd, Error **errp)
> > >      return qemu_socket_select(sockfd, NULL, 0, errp);
> > >  }
> > >
> > > +int qemu_socketpair(int domain, int type, int protocol, int sv[2])
> > > +{
> > > +    struct sockaddr_un addr = {
> > > +        0,
> > > +    };
> > > +    socklen_t socklen;
> > > +    int listener = -1;
> > > +    int client = -1;
> > > +    int server = -1;
> > > +    g_autofree char *path = NULL;
> > > +    int tmpfd;
> > > +    u_long arg;
> > > +    int ret = -1;
> > > +
> > > +    g_return_val_if_fail(sv != NULL, -1);
> > > +
> > > +    addr.sun_family = AF_UNIX;
> > > +    socklen = sizeof(addr);
> > > +
> > > +    tmpfd = g_file_open_tmp(NULL, &path, NULL);
> > > +    if (tmpfd == -1 || !path) {
> > > +        errno = EACCES;
> > > +        goto out;
> > > +    }
> > > +
> > > +    close(tmpfd);
> > > +
> > > +    if (strlen(path) >= sizeof(addr.sun_path)) {
> > > +        errno = EINVAL;
> > > +        goto out;
> > > +    }
> > > +
> > > +    strncpy(addr.sun_path, path, sizeof(addr.sun_path) - 1);
> > > +
> > > +    listener = socket(domain, type, protocol);
> > > +    if (listener == -1) {
> > > +        goto out;
> > > +    }
> > > +
> > > +    if (DeleteFile(path) == 0 && GetLastError() != ERROR_FILE_NOT_FOUND) {
> > > +        errno = EACCES;
> > > +        goto out;
> > > +    }
> > > +    g_clear_pointer(&path, g_free);
> > > +
> > > +    if (bind(listener, (struct sockaddr *)&addr, socklen) == -1) {
> > > +        goto out;
> > > +    }
> > > +
> > > +    if (listen(listener, 1) == -1) {
> > > +        goto out;
> > > +    }
> > > +
> > > +    client = socket(domain, type, protocol);
> > > +    if (client == -1) {
> > > +        goto out;
> > > +    }
> > > +
> > > +    arg = 1;
> > > +    if (ioctlsocket(client, FIONBIO, &arg) != NO_ERROR) {
> > > +        goto out;
> > > +    }
> > > +
> > > +    if (connect(client, (struct sockaddr *)&addr, socklen) == -1 &&
> > > +        WSAGetLastError() != WSAEWOULDBLOCK) {
> > > +        goto out;
> > > +    }
> > > +
> > > +    server = accept(listener, NULL, NULL);
> > > +    if (server == -1) {
> > > +        goto out;
> > > +    }
> >
> > In theory at this point 'client' if connect() returned WSAEWOULDBLOCK,
> > then at this point it should be fully connected. I wonder if that is
> > actually guaranteed though, or should we do something to validate
> > there's no race condition ?
> >
> > > +
> > > +    arg = 0;
> > > +    if (ioctlsocket(client, FIONBIO, &arg) != NO_ERROR) {
> > > +        goto out;
> > > +    }
> > > +
> > > +    arg = 0;
> > > +    if (ioctlsocket(client, SIO_AF_UNIX_GETPEERPID, &arg) != NO_ERROR) {
> > > +        goto out;
> > > +    }
> >
> > Maybe this will force a synchronization point ?
> 
> yeah, I guess switching back to sync and getting the peer pid,
> 
> I assume the unix socket pair to be ready at this point.

Ok, lets hope its ok, but remember this if we see any non-deterministic
failures 

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>



With regards,
Daniel
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