lkml.org 
[lkml]   [2012]   [Jan]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    SubjectRe: [Xen-devel] [PATCH 2/2] hvc_xen: implement multiconsole support
    On Fri, Jan 27, 2012 at 05:16:45PM +0000, Stefano Stabellini wrote:
    > On Fri, 27 Jan 2012, Konrad Rzeszutek Wilk wrote:
    > > On Thu, Jan 26, 2012 at 12:43:27PM +0000, Stefano Stabellini wrote:
    > > > This patch implements support for multiple consoles:
    > > > consoles other than the first one are setup using the traditional xenbus
    > > > and grant-table based mechanism.
    > > > We use a list to keep track of the allocated consoles, we don't
    > > > expect too many of them anyway.
    > > >
    > > > Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
    > > > ---
    > > > drivers/tty/hvc/hvc_xen.c | 439 +++++++++++++++++++++++++++++++++++++++------
    > > > 1 files changed, 383 insertions(+), 56 deletions(-)
    > > >
    > > > diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
    > > > index dd6641f..97732fb 100644
    > > > --- a/drivers/tty/hvc/hvc_xen.c
    > > > +++ b/drivers/tty/hvc/hvc_xen.c
    > > > @@ -23,6 +23,7 @@
    > > > #include <linux/err.h>
    > > > #include <linux/init.h>
    > > > #include <linux/types.h>
    > > > +#include <linux/list.h>
    > > >
    > > > #include <asm/io.h>
    > > > #include <asm/xen/hypervisor.h>
    > > > @@ -30,47 +31,69 @@
    > > > #include <xen/xen.h>
    > > > #include <xen/interface/xen.h>
    > > > #include <xen/hvm.h>
    > > > +#include <xen/grant_table.h>
    > > > #include <xen/page.h>
    > > > #include <xen/events.h>
    > > > #include <xen/interface/io/console.h>
    > > > #include <xen/hvc-console.h>
    > > > +#include <xen/xenbus.h>
    > > >
    > > > #include "hvc_console.h"
    > > >
    > > > #define HVC_COOKIE 0x58656e /* "Xen" in hex */
    > > >
    > > > -static struct hvc_struct *hvc;
    > > > -static int xencons_irq;
    > > > +struct xencons_info {
    > > > + struct list_head list;
    > > > + struct xenbus_device *xbdev;
    > > > + struct xencons_interface *intf;
    > > > + unsigned int evtchn;
    > > > + struct hvc_struct *hvc;
    > > > + int irq;
    > > > + int vtermno;
    > > > + grant_ref_t gntref;
    > > > +};
    > > > +
    > > > +static LIST_HEAD(xenconsoles);
    > > > +static DEFINE_SPINLOCK(xencons_lock);
    > > > +static struct xenbus_driver xencons_driver;
    > > >
    > > > /* ------------------------------------------------------------------ */
    > > >
    > > > -static unsigned long console_pfn = ~0ul;
    > > > -static unsigned int console_evtchn = ~0ul;
    > > > -static struct xencons_interface *xencons_if = NULL;
    > > > +static struct xencons_info *vtermno_to_xencons(int vtermno)
    > > > +{
    > > > + struct xencons_info *entry, *ret = NULL;
    > > > +
    > > > + if (list_empty(&xenconsoles))
    > > > + return NULL;
    > > >
    > > > -static inline struct xencons_interface *xencons_interface(void)
    > > > + spin_lock(&xencons_lock);
    > >
    > > This spinlock gets hit everytime something is typed or written on the
    > > console right? Isn't there an spinlock already in the hvc driver...
    > >
    > > Or are we protected by the vtermnos being checked for -1?
    >
    > I think you are right: the spinlock is there to protect access to the
    > list, so we can change list_for_each_entry to list_for_each_entry_safe
    > in vtermno_to_xencons and we solve the problem. All the other spinlock
    > acquisitions are done at console creation/destruction.

    Right. So I think this will work as long as you mkae the call
    to hvc_remove _before_ your remove entries from the xenconsoles.

    That way hvc_remove will set vtermnos[x] to -1 and inhibit
    any callers from calling into us.

    This means you will need to redo the xencons_remove and xencons_free
    a bit.. Hmm, there looks to be dead-lock there - let me send the
    details.


    \
     
     \ /
      Last update: 2012-01-27 19:39    [W:0.029 / U:103.976 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site