Xen devel - Feb 2013 - Implementing poll(2) for Mini-OS?

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?

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);

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);
> 
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel

On Mon, 2013-02-18 at 16:06 +0000, Ian Campbell wrote:
> 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.
> 
Hah? This is my first impression, but we still need a xenstored running
in Dom0, right? Otherwise what''s the output of `xenstore-ls` in Dom0?
> 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!
> 
Xenstore has a struct connection which has one fd for each connection.
So if there are too many connections, how can xenstore stubdom handle
this situation? As I can see in a xenstore process running in Dom0, it
can certainly opens more than 32 fds.


Wei.
> > 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);
> > 
> > 
> > 
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@lists.xen.org
> > http://lists.xen.org/xen-devel
> 
>

On Mon, 2013-02-18 at 16:18 +0000, Wei Liu wrote:
> On Mon, 2013-02-18 at 16:06 +0000, Ian Campbell wrote:
> > 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.
> > 
> 
> Hah? This is my first impression, but we still need a xenstored running
> in Dom0, right?
No
>  Otherwise what''s the output of `xenstore-ls` in Dom0?
It talks to the remote stubdom, in the same way that a domU normally
would.

There is only one xenstored in the entire system. (Ignoring extreme
disaggregation like the XOAR paper).
> > 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!
> > 
> 
> Xenstore has a struct connection which has one fd for each connection.
> So if there are too many connections, how can xenstore stubdom handle
> this situation? As I can see in a xenstore process running in Dom0, it
> can certainly opens more than 32 fds.
In theory it could share the same /dev/xen/evtchn handle between all
connections.

Ian.

On Mon, 2013-02-18 at 16:25 +0000, Ian Campbell wrote:
> On Mon, 2013-02-18 at 16:18 +0000, Wei Liu wrote:
> > On Mon, 2013-02-18 at 16:06 +0000, Ian Campbell wrote:
> > > 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.
> > > 
> > 
> > Hah? This is my first impression, but we still need a xenstored
running
> > in Dom0, right?
> 
> No
> 
> >  Otherwise what''s the output of `xenstore-ls` in Dom0?
> 
> It talks to the remote stubdom, in the same way that a domU normally
> would.
> 
> There is only one xenstored in the entire system. (Ignoring extreme
> disaggregation like the XOAR paper).
> 
OK.
> > > 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!
> > > 
> > 
> > Xenstore has a struct connection which has one fd for each connection.
> > So if there are too many connections, how can xenstore stubdom handle
> > this situation? As I can see in a xenstore process running in Dom0, it
> > can certainly opens more than 32 fds.
> 
> In theory it could share the same /dev/xen/evtchn handle between all
> connections.
> 
I think the real magic is that in cxenstore''s implementation there is
some ifdef around specific code to avoid using too many fds, but I
haven''t gone too deep into that...


Wei.
> Ian.
>

On Mon, 2013-02-18 at 17:05 +0000, Wei Liu wrote:
> On Mon, 2013-02-18 at 16:25 +0000, Ian Campbell wrote:
> > On Mon, 2013-02-18 at 16:18 +0000, Wei Liu wrote:
> > > On Mon, 2013-02-18 at 16:06 +0000, Ian Campbell wrote:
> > > > 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.
> > > > 
> > > 
> > > Hah? This is my first impression, but we still need a xenstored
running
> > > in Dom0, right?
> > 
> > No
> > 
> > >  Otherwise what''s the output of `xenstore-ls` in Dom0?
> > 
> > It talks to the remote stubdom, in the same way that a domU normally
> > would.
> > 
> > There is only one xenstored in the entire system. (Ignoring extreme
> > disaggregation like the XOAR paper).
> > 
> 
> OK.
> 
> > > > 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!
> > > > 
> > > 
> > > Xenstore has a struct connection which has one fd for each
connection.
> > > So if there are too many connections, how can xenstore stubdom
handle
> > > this situation? As I can see in a xenstore process running in
Dom0, it
> > > can certainly opens more than 32 fds.
> > 
> > In theory it could share the same /dev/xen/evtchn handle between all
> > connections.
> > 
> 
> I think the real magic is that in cxenstore''s implementation there
is
> some ifdef around specific code to avoid using too many fds, but I
> haven''t gone too deep into that...
> 
Oops, hit send for a mis-composted email, please ignore this... I''m
still investigating this.


Wei.

Wei Liu, le Mon 18 Feb 2013 15:40:56 +0000, a écrit :
> I sent a patch to switch cxenstored''s event loop from using select
to
> using poll several weeks ago,
What is the rationale BTW?  Efficiency?
> 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)
Yes, except that there are evil small differences between poll and
select, which we need to take care of.

About the 32 fd limitation, it indeed comes from the days when we always
had a bounded number of things to open.  We need to drop that limitation,
but it should be easy, by turning the `files'' array into a reallocable
pointer.  There is just one important thing: the xenbus_event_queue
events field has to be made a pointer to a dynamically-allocated queue,
otherwise it will get moved by the reallocation and things will go wrong
very badly.
> +int poll(struct pollfd pfd[], int nfds, int timeout)
> +{
...
> +
> +    /* Timeout in poll is in second. */
> +    _timeo.tv_sec  = timeout;
FIXME: timeout is in ms, not sec.
> +    _timeo.tv_usec = 0;
Samuel

On Mon, 2013-02-18 at 17:12 +0000, Samuel Thibault
wrote:
> Wei Liu, le Mon 18 Feb 2013 15:40:56 +0000, a écrit :
> > I sent a patch to switch cxenstored's event loop from using select
to
> > using poll several weeks ago,
> 
> What is the rationale BTW?  Efficiency?
> 
Oh, the rationale is that select can only support 1024 fds in Linux. If
we run more than 1024 guest (in fact the real limit is like 1022),
xenstore hangs and makes the whole system unusable.
> > 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)
> 
> Yes, except that there are evil small differences between poll and
> select, which we need to take care of.
> 
Sure. :-)
> About the 32 fd limitation, it indeed comes from the days when we always
> had a bounded number of things to open.  We need to drop that limitation,
> but it should be easy, by turning the `files' array into a reallocable
> pointer.  There is just one important thing: the xenbus_event_queue
> events field has to be made a pointer to a dynamically-allocated queue,
> otherwise it will get moved by the reallocation and things will go wrong
> very badly.
> 
So apart from the modification needed, is this "32" really a
bottleneck
for xenstore-stubdom? How many domains can a xenstore-stubdom serve? (I
think these two questions are for Daniel)


Wei.


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On Mon, 2013-02-18 at 17:21 +0000, Wei Liu wrote:
> So apart from the modification needed, is this "32" really a
bottleneck
> for xenstore-stubdom? How many domains can a xenstore-stubdom serve?
There''s no reason in principal to expect this to be any less than
xenstored running in dom0 can support, issues like the one you''ve found
notwithstanding.

Ian.

Wei Liu, le Mon 18 Feb 2013 17:21:02 +0000, a écrit :
> So apart from the modification needed, is this "32" really a
bottleneck
> for xenstore-stubdom?
Actually I don''t think it is: from what I see in the xenstore source,
different FDs are only used for connexions on the unix-connexion
socket, but for stubdoms, such socket does not make sense and is thus
disabled anyway.  So NOFILE being 32 is actually not an issue at all for
xenstore-stubdom.

Samuel

Wei Liu, le Mon 18 Feb 2013 15:40:56 +0000, a écrit :
> +    ret = select(&rfds, &wfds, NULL, &_timeo);
> +
> +    for (i = 0; i < nfds; i++) {
> +        fd = pfd[i].fd;
Here we have to set revents to 0 before adding some bits. The caller may
not have cleared revents already.
> +	if (FD_ISSET(fd, &rfds))
> +            pfd[i].revents |= POLLIN;
> +	if (FD_ISSET(fd, &wfds))
> +            pfd[i].revents |= POLLOUT;
> +    }
Samuel