Re: [Xen-devel] Implementing poll(2) for Mini-OS?

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2013-02-18 at 15:40 +0000, Wei Liu wrote:
> Hi Samuel and Daniel
> 
> I sent a patch to switch cxenstored's event loop from using select to
> using poll several weeks ago, however this would break xenstore-stubdom
> as Mini-OS has no poll(2) implementation at the moment.
> 
> I think implementing poll(2) for Mini-OS could be a good idea, but I
> don't know how far I should go. I'm not familiar with xenstore-stubdom,
> and I tried setting it up but it didn't work so I gave up. :-(
> 
> To my understanding we only care about the interface but not the
> implementation. I looked into Mini-OS's lib/sys.c this morning, noticing
> that the internal file abstraction only supports up to 32 files. Is this
> xenstore-stubdom only for DomU? If it is for Dom0, how can it handle
> more than 32 fds?

What do you mean? A stubdom must necessarily be dom!=0 but it should be
able to service all other domains, including dom0 and other domUs.

Do we use an fd per evtchn or only one in xenstore? If the former then
that's a bit of a limitation of the xenstore stubdom!

> My main question is, is it possible to just wrap around select(2) in
> Mini-OS to implement poll(2)? (as shown in the conceptual patch)
> 
> 
> 
> Wei.
> 
> conceptual patch like this:
> -----8<----
> diff --git a/extras/mini-os/lib/sys.c b/extras/mini-os/lib/sys.c
> index 3cc3340..d463231 100644
> --- a/extras/mini-os/lib/sys.c
> +++ b/extras/mini-os/lib/sys.c
> @@ -678,6 +678,29 @@ static void dump_set(int nfds, fd_set *readfds, fd_set 
> *writefds, fd_set *except
>  #define dump_set(nfds, readfds, writefds, exceptfds, timeout)
>  #endif
>  
> +#ifdef LIBC_DEBUG
> +static void dump_pollfds(struct pollfd *pfd, int nfds, int timeout)
> +{
> +    int i, comma, fd;
> +
> +    printk("[");
> +    comma = 0;
> +    for (i = 0; i < nfds; i++) {
> +      fd = pfd[i].fd;
> +      if (comma)
> +           printk(", ");
> +      printk("%d(%c)/%02x", fd, file_types[files[fd].type],
> +             pfd[i].events);
> +         comma = 1;
> +    }
> +    printk("]");
> +
> +    printk(", %d, %d", nfds, timeout);
> +}
> +#else
> +#define dump_pollfds(pfds, nfds, timeout)
> +#endif
> +
>  /* Just poll without blocking */
>  static int select_poll(int nfds, fd_set *readfds, fd_set *writefds, fd_set 
> *exceptfds)
>  {
> @@ -983,6 +1006,53 @@ out:
>      return ret;
>  }
>  
> +/*
> + * As Mini-OS only supports NOFILE files, we can just wrap around
> + * select?
> + */
> +int poll(struct pollfd pfd[], int nfds, int timeout)
> +{
> +    int ret;
> +    int i, fd;
> +    struct timeval _timeo;
> +    fd_set rfds, wfds;
> +
> +    DEBUG("poll(");
> +    dump_pollfds(pfd, nfds, timeout);
> +    DEBUG(")\n");
> +
> +    /* Timeout in poll is in second. */
> +    _timeo.tv_sec  = timeout;
> +    _timeo.tv_usec = 0;
> +
> +    FD_ZERO(&rfds);
> +    FD_ZERO(&wfds);
> +
> +    for (i = 0; i < nfds; i++) {
> +        fd = pfd[i].fd;
> +     if (pfd[i].events & POLLIN)
> +            FD_SET(fd, &rfds);
> +     if (pfd[i].events & POLLOUT)
> +            FD_SET(fd, &wfds);
> +    }
> +
> +    ret = select(&rfds, &wfds, NULL, &_timeo);
> +
> +    for (i = 0; i < nfds; i++) {
> +        fd = pfd[i].fd;
> +     if (FD_ISSET(fd, &rfds))
> +            pfd[i].revents |= POLLIN;
> +     if (FD_ISSET(fd, &wfds))
> +            pfd[i].revents |= POLLOUT;
> +    }
> +
> +    DEBUG("poll(");
> +    dump_pollfds(pfd, nfds, timeout);
> +    DEBUG(")\n");
> +
> +    return ret;
> +}
> +
>  #ifdef HAVE_LWIP
>  int socket(int domain, int type, int protocol)
>  {
> @@ -1360,7 +1430,6 @@ unsupported_function(int, tcgetattr, 0);
>  unsupported_function(int, grantpt, -1);
>  unsupported_function(int, unlockpt, -1);
>  unsupported_function(char *, ptsname, NULL);
> -unsupported_function(int, poll, -1);
>  
>  /* net/if.h */
>  unsupported_function_log(unsigned int, if_nametoindex, -1);
> 
> 
> 
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> http://lists.xen.org/xen-devel



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