[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] libxl: create control/sysrq xenstore node
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@xxxxxxxxxx> 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@xxxxxxxxxx> > > > > > > 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. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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