* [PATCH] libxl: create control/sysrq xenstore node
@ 2018-09-04 11:39 Vitaly Kuznetsov
2018-09-04 16:51 ` Wei Liu
2018-09-05 8:22 ` Wei Liu
0 siblings, 2 replies; 7+ messages in thread
From: Vitaly Kuznetsov @ 2018-09-04 11:39 UTC (permalink / raw)
To: xen-devel; +Cc: Ian Jackson, Wei Liu
'xl sysrq' command doesn't work with modern Linux guests with the following
message in guest's log:
xen:manage: sysrq_handler: Error -13 writing sysrq in control/sysrq
xenstore trace confirms:
IN 0x24bd9a0 20180904 04:36:32 WRITE (control/sysrq )
OUT 0x24bd9a0 20180904 04:36:32 ERROR (EACCES )
The problem seems to be in the fact that we don't pre-create control/sysrq
xenstore node and libxl_send_sysrq() doing libxl__xs_printf() creates it as
read-only. As we want to allow guests to clean 'control/sysrq' after the
requested action is performed, we need to make this node writable.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
- Linux code will need to be modified too. With this patch we get something
like
sysrq: SysRq : Emergency Sync
xen:manage: Error -34 reading sysrq code in control/sysrq
Emergency Sync complete
This new ERANGE fault happens because after we clean control/sysrq node
xenstore watch in the guest is re-asserted but the value is empty ("") so
xenbus_scanf() fails "%c" parsing.
It seems the feature is long broken.
---
tools/libxl/libxl_create.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index b7b44e280b..d60f952f73 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -692,6 +692,9 @@ retry_transaction:
GCSPRINTF("%s/control/feature-s4", dom_path),
rwperm, ARRAY_SIZE(rwperm));
}
+ libxl__xs_mknod(gc, t,
+ GCSPRINTF("%s/control/sysrq", dom_path),
+ rwperm, ARRAY_SIZE(rwperm));
libxl__xs_mknod(gc, t,
GCSPRINTF("%s/device/suspend/event-channel", dom_path),
rwperm, ARRAY_SIZE(rwperm));
--
2.14.4
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^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH] libxl: create control/sysrq xenstore node
2018-09-04 11:39 [PATCH] libxl: create control/sysrq xenstore node Vitaly Kuznetsov
@ 2018-09-04 16:51 ` Wei Liu
2018-09-04 17:27 ` Vitaly Kuznetsov
2018-09-05 8:22 ` Wei Liu
1 sibling, 1 reply; 7+ messages in thread
From: Wei Liu @ 2018-09-04 16:51 UTC (permalink / raw)
To: Vitaly Kuznetsov; +Cc: xen-devel, Wei Liu, Ian Jackson
On Tue, Sep 04, 2018 at 01:39:29PM +0200, Vitaly Kuznetsov wrote:
> 'xl sysrq' command doesn't work with modern Linux guests with the following
> message in guest's log:
>
> xen:manage: sysrq_handler: Error -13 writing sysrq in control/sysrq
>
> xenstore trace confirms:
>
> IN 0x24bd9a0 20180904 04:36:32 WRITE (control/sysrq )
> OUT 0x24bd9a0 20180904 04:36:32 ERROR (EACCES )
>
> The problem seems to be in the fact that we don't pre-create control/sysrq
> xenstore node and libxl_send_sysrq() doing libxl__xs_printf() creates it as
> read-only. As we want to allow guests to clean 'control/sysrq' after the
> requested action is performed, we need to make this node writable.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Hmm... this node isn't documented.
Can you point me to the code in Linux?
> ---
> - Linux code will need to be modified too. With this patch we get something
> like
>
> sysrq: SysRq : Emergency Sync
> xen:manage: Error -34 reading sysrq code in control/sysrq
> Emergency Sync complete
>
> This new ERANGE fault happens because after we clean control/sysrq node
> xenstore watch in the guest is re-asserted but the value is empty ("") so
> xenbus_scanf() fails "%c" parsing.
>
> It seems the feature is long broken.
> ---
> tools/libxl/libxl_create.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
> index b7b44e280b..d60f952f73 100644
> --- a/tools/libxl/libxl_create.c
> +++ b/tools/libxl/libxl_create.c
> @@ -692,6 +692,9 @@ retry_transaction:
> GCSPRINTF("%s/control/feature-s4", dom_path),
> rwperm, ARRAY_SIZE(rwperm));
> }
> + libxl__xs_mknod(gc, t,
> + GCSPRINTF("%s/control/sysrq", dom_path),
> + rwperm, ARRAY_SIZE(rwperm));
> libxl__xs_mknod(gc, t,
> GCSPRINTF("%s/device/suspend/event-channel", dom_path),
> rwperm, ARRAY_SIZE(rwperm));
> --
> 2.14.4
>
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^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] libxl: create control/sysrq xenstore node
2018-09-04 16:51 ` Wei Liu
@ 2018-09-04 17:27 ` Vitaly Kuznetsov
2018-09-05 8:22 ` Wei Liu
0 siblings, 1 reply; 7+ messages in thread
From: Vitaly Kuznetsov @ 2018-09-04 17:27 UTC (permalink / raw)
To: Wei Liu; +Cc: xen-devel, Ian Jackson
Wei Liu <wei.liu2@citrix.com> writes:
> On Tue, Sep 04, 2018 at 01:39:29PM +0200, Vitaly Kuznetsov wrote:
>> 'xl sysrq' command doesn't work with modern Linux guests with the following
>> message in guest's log:
>>
>> xen:manage: sysrq_handler: Error -13 writing sysrq in control/sysrq
>>
>> xenstore trace confirms:
>>
>> IN 0x24bd9a0 20180904 04:36:32 WRITE (control/sysrq )
>> OUT 0x24bd9a0 20180904 04:36:32 ERROR (EACCES )
>>
>> The problem seems to be in the fact that we don't pre-create control/sysrq
>> xenstore node and libxl_send_sysrq() doing libxl__xs_printf() creates it as
>> read-only. As we want to allow guests to clean 'control/sysrq' after the
>> requested action is performed, we need to make this node writable.
>>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>
> Hmm... this node isn't documented.
>
But libxl already writes it, see libxl_send_sysrq().
> Can you point me to the code in Linux?
>
Sure,
drivers/xen/manage.c:
static void sysrq_handler(struct xenbus_watch *watch, const char *path,
const char *token)
{
char sysrq_key = '\0';
struct xenbus_transaction xbt;
int err;
again:
err = xenbus_transaction_start(&xbt);
if (err)
return;
err = xenbus_scanf(xbt, "control", "sysrq", "%c", &sysrq_key);
if (err < 0) {
/*
* The Xenstore watch fires directly after registering it and
* after a suspend/resume cycle. So ENOENT is no error but
* might happen in those cases.
*/
if (err != -ENOENT)
pr_err("Error %d reading sysrq code in control/sysrq\n",
err);
xenbus_transaction_end(xbt, 1);
return;
}
if (sysrq_key != '\0') {
err = xenbus_printf(xbt, "control", "sysrq", "%c", '\0');
if (err) {
pr_err("%s: Error %d writing sysrq in control/sysrq\n",
__func__, err);
xenbus_transaction_end(xbt, 1);
return;
}
}
err = xenbus_transaction_end(xbt, 0);
if (err == -EAGAIN)
goto again;
if (sysrq_key != '\0')
handle_sysrq(sysrq_key);
}
static struct xenbus_watch sysrq_watch = {
.node = "control/sysrq",
.callback = sysrq_handler
};
--
Vitaly
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^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] libxl: create control/sysrq xenstore node
2018-09-04 17:27 ` Vitaly Kuznetsov
@ 2018-09-05 8:22 ` Wei Liu
2018-09-05 10:12 ` Roger Pau Monné
2018-09-05 10:15 ` Vitaly Kuznetsov
0 siblings, 2 replies; 7+ messages in thread
From: Wei Liu @ 2018-09-05 8:22 UTC (permalink / raw)
To: Vitaly Kuznetsov
Cc: Juergen Gross, Wei Liu, Ian Jackson, xen-devel, Boris Ostrovsky,
Roger Pau Monné
Also CC Linux maintainers.
On Tue, Sep 04, 2018 at 07:27:31PM +0200, Vitaly Kuznetsov wrote:
> Wei Liu <wei.liu2@citrix.com> writes:
>
> > On Tue, Sep 04, 2018 at 01:39:29PM +0200, Vitaly Kuznetsov wrote:
> >> 'xl sysrq' command doesn't work with modern Linux guests with the following
> >> message in guest's log:
> >>
> >> xen:manage: sysrq_handler: Error -13 writing sysrq in control/sysrq
> >>
> >> xenstore trace confirms:
> >>
> >> IN 0x24bd9a0 20180904 04:36:32 WRITE (control/sysrq )
> >> OUT 0x24bd9a0 20180904 04:36:32 ERROR (EACCES )
> >>
> >> The problem seems to be in the fact that we don't pre-create control/sysrq
> >> xenstore node and libxl_send_sysrq() doing libxl__xs_printf() creates it as
> >> read-only. As we want to allow guests to clean 'control/sysrq' after the
> >> requested action is performed, we need to make this node writable.
> >>
> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> >
> > Hmm... this node isn't documented.
> >
>
> But libxl already writes it, see libxl_send_sysrq().
I think your patch is fine.
What I wanted to do is to document this node. :p
>
> > Can you point me to the code in Linux?
> >
>
> Sure,
>
> drivers/xen/manage.c:
Alright, it appears DomU only expects a single character to be written.
I have written the following diff, do you think it is sensible? I
believe this is Linux only, but I have CC Roger for correction.
diff --git a/docs/misc/xenstore-paths.markdown b/docs/misc/xenstore-paths.markdown
index 60c8b3fbe5..33d281915c 100644
--- a/docs/misc/xenstore-paths.markdown
+++ b/docs/misc/xenstore-paths.markdown
@@ -410,6 +410,14 @@ by udev ("0") or will be run by the toolstack directly ("1").
### Platform Feature and Control Paths
+#### ~/control/sysrq = (""|COMMAND) [w]
+
+This is the PV SysRq control node. A toolstack can write a single character
+representing a magic SysRq key understood by the Linux kernel. The guest
+acknowledges a request by writing the empty string back to the command node.
+
+This protocol is Linux only.
+
#### ~/control/shutdown = (""|COMMAND) [w]
This is the PV shutdown control node. A toolstack can write various
Wei.
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^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH] libxl: create control/sysrq xenstore node
2018-09-05 8:22 ` Wei Liu
@ 2018-09-05 10:12 ` Roger Pau Monné
2018-09-05 10:15 ` Vitaly Kuznetsov
1 sibling, 0 replies; 7+ messages in thread
From: Roger Pau Monné @ 2018-09-05 10:12 UTC (permalink / raw)
To: Wei Liu
Cc: Juergen Gross, xen-devel, Vitaly Kuznetsov, Ian Jackson, Boris Ostrovsky
On Wed, Sep 05, 2018 at 09:22:03AM +0100, Wei Liu wrote:
> Also CC Linux maintainers.
>
> On Tue, Sep 04, 2018 at 07:27:31PM +0200, Vitaly Kuznetsov wrote:
> > Wei Liu <wei.liu2@citrix.com> writes:
> >
> > > On Tue, Sep 04, 2018 at 01:39:29PM +0200, Vitaly Kuznetsov wrote:
> > >> 'xl sysrq' command doesn't work with modern Linux guests with the following
> > >> message in guest's log:
> > >>
> > >> xen:manage: sysrq_handler: Error -13 writing sysrq in control/sysrq
> > >>
> > >> xenstore trace confirms:
> > >>
> > >> IN 0x24bd9a0 20180904 04:36:32 WRITE (control/sysrq )
> > >> OUT 0x24bd9a0 20180904 04:36:32 ERROR (EACCES )
> > >>
> > >> The problem seems to be in the fact that we don't pre-create control/sysrq
> > >> xenstore node and libxl_send_sysrq() doing libxl__xs_printf() creates it as
> > >> read-only. As we want to allow guests to clean 'control/sysrq' after the
> > >> requested action is performed, we need to make this node writable.
> > >>
> > >> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> > >
> > > Hmm... this node isn't documented.
> > >
> >
> > But libxl already writes it, see libxl_send_sysrq().
>
> I think your patch is fine.
>
> What I wanted to do is to document this node. :p
>
> >
> > > Can you point me to the code in Linux?
> > >
> >
> > Sure,
> >
> > drivers/xen/manage.c:
>
> Alright, it appears DomU only expects a single character to be written.
>
> I have written the following diff, do you think it is sensible? I
> believe this is Linux only, but I have CC Roger for correction.
>
>
> diff --git a/docs/misc/xenstore-paths.markdown b/docs/misc/xenstore-paths.markdown
> index 60c8b3fbe5..33d281915c 100644
> --- a/docs/misc/xenstore-paths.markdown
> +++ b/docs/misc/xenstore-paths.markdown
> @@ -410,6 +410,14 @@ by udev ("0") or will be run by the toolstack directly ("1").
>
> ### Platform Feature and Control Paths
>
> +#### ~/control/sysrq = (""|COMMAND) [w]
> +
> +This is the PV SysRq control node. A toolstack can write a single character
> +representing a magic SysRq key understood by the Linux kernel. The guest
> +acknowledges a request by writing the empty string back to the command node.
> +
> +This protocol is Linux only.
> +
> #### ~/control/shutdown = (""|COMMAND) [w]
>
> This is the PV shutdown control node. A toolstack can write various
LGTM. I haven't implemented this on FreeBSD, and I very much doubt
NetBSD uses it at all. FreeBSD doesn't have such thing as sysrq keys,
there's only a key sequence used in order to break into the debugger from
the console AFAIK.
Roger.
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^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] libxl: create control/sysrq xenstore node
2018-09-05 8:22 ` Wei Liu
2018-09-05 10:12 ` Roger Pau Monné
@ 2018-09-05 10:15 ` Vitaly Kuznetsov
1 sibling, 0 replies; 7+ messages in thread
From: Vitaly Kuznetsov @ 2018-09-05 10:15 UTC (permalink / raw)
To: Wei Liu
Cc: Juergen Gross, xen-devel, Boris Ostrovsky, Ian Jackson,
Roger Pau Monné
Wei Liu <wei.liu2@citrix.com> writes:
> Also CC Linux maintainers.
>
> On Tue, Sep 04, 2018 at 07:27:31PM +0200, Vitaly Kuznetsov wrote:
>> Wei Liu <wei.liu2@citrix.com> writes:
>>
>> > On Tue, Sep 04, 2018 at 01:39:29PM +0200, Vitaly Kuznetsov wrote:
>> >> 'xl sysrq' command doesn't work with modern Linux guests with the following
>> >> message in guest's log:
>> >>
>> >> xen:manage: sysrq_handler: Error -13 writing sysrq in control/sysrq
>> >>
>> >> xenstore trace confirms:
>> >>
>> >> IN 0x24bd9a0 20180904 04:36:32 WRITE (control/sysrq )
>> >> OUT 0x24bd9a0 20180904 04:36:32 ERROR (EACCES )
>> >>
>> >> The problem seems to be in the fact that we don't pre-create control/sysrq
>> >> xenstore node and libxl_send_sysrq() doing libxl__xs_printf() creates it as
>> >> read-only. As we want to allow guests to clean 'control/sysrq' after the
>> >> requested action is performed, we need to make this node writable.
>> >>
>> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> >
>> > Hmm... this node isn't documented.
>> >
>>
>> But libxl already writes it, see libxl_send_sysrq().
>
> I think your patch is fine.
>
> What I wanted to do is to document this node. :p
>
>>
>> > Can you point me to the code in Linux?
>> >
>>
>> Sure,
>>
>> drivers/xen/manage.c:
>
> Alright, it appears DomU only expects a single character to be written.
>
> I have written the following diff, do you think it is sensible? I
> believe this is Linux only, but I have CC Roger for correction.
>
> diff --git a/docs/misc/xenstore-paths.markdown b/docs/misc/xenstore-paths.markdown
> index 60c8b3fbe5..33d281915c 100644
> --- a/docs/misc/xenstore-paths.markdown
> +++ b/docs/misc/xenstore-paths.markdown
> @@ -410,6 +410,14 @@ by udev ("0") or will be run by the toolstack directly ("1").
>
> ### Platform Feature and Control Paths
>
> +#### ~/control/sysrq = (""|COMMAND) [w]
> +
> +This is the PV SysRq control node. A toolstack can write a single character
> +representing a magic SysRq key understood by the Linux kernel. The guest
> +acknowledges a request by writing the empty string back to the command node.
> +
> +This protocol is Linux only.
> +
> #### ~/control/shutdown = (""|COMMAND) [w]
>
Makes perfect sense to me and sounds correct, thanks!
--
Vitaly
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^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] libxl: create control/sysrq xenstore node
2018-09-04 11:39 [PATCH] libxl: create control/sysrq xenstore node Vitaly Kuznetsov
2018-09-04 16:51 ` Wei Liu
@ 2018-09-05 8:22 ` Wei Liu
1 sibling, 0 replies; 7+ messages in thread
From: Wei Liu @ 2018-09-05 8:22 UTC (permalink / raw)
To: Vitaly Kuznetsov; +Cc: xen-devel, Wei Liu, Ian Jackson
On Tue, Sep 04, 2018 at 01:39:29PM +0200, Vitaly Kuznetsov wrote:
> 'xl sysrq' command doesn't work with modern Linux guests with the following
> message in guest's log:
>
> xen:manage: sysrq_handler: Error -13 writing sysrq in control/sysrq
>
> xenstore trace confirms:
>
> IN 0x24bd9a0 20180904 04:36:32 WRITE (control/sysrq )
> OUT 0x24bd9a0 20180904 04:36:32 ERROR (EACCES )
>
> The problem seems to be in the fact that we don't pre-create control/sysrq
> xenstore node and libxl_send_sysrq() doing libxl__xs_printf() creates it as
> read-only. As we want to allow guests to clean 'control/sysrq' after the
> requested action is performed, we need to make this node writable.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
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^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2018-09-05 10:16 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-09-04 11:39 [PATCH] libxl: create control/sysrq xenstore node Vitaly Kuznetsov
2018-09-04 16:51 ` Wei Liu
2018-09-04 17:27 ` Vitaly Kuznetsov
2018-09-05 8:22 ` Wei Liu
2018-09-05 10:12 ` Roger Pau Monné
2018-09-05 10:15 ` Vitaly Kuznetsov
2018-09-05 8:22 ` Wei Liu
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