[Xen-devel] [PATCH] xenconsoled: use grant references instead of map_foreign_range

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

Grant references for the xenstore and xenconsole shared pages exist, but
currently only xenstore uses these references.  Change the xenconsole
daemon to prefer using the grant reference over map_foreign_range when
mapping the shared console ring.

This allows xenconsoled to be run in a domain other than dom0 if set up
correctly - for libxl, the xenstore path /tool/xenconsoled/domid
specifies the domain containing xenconsoled.

Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
 tools/console/daemon/io.c | 45 +++++++++++++++++++++++++++++++++++++++------
 1 file changed, 39 insertions(+), 6 deletions(-)

diff --git a/tools/console/daemon/io.c b/tools/console/daemon/io.c
index 48fe151..e24247d 100644
--- a/tools/console/daemon/io.c
+++ b/tools/console/daemon/io.c
@@ -24,6 +24,7 @@
 #include "io.h"
 #include <xenstore.h>
 #include <xen/io/console.h>
+#include <xen/grant_table.h>
 
 #include <stdlib.h>
 #include <errno.h>
@@ -69,6 +70,7 @@ static int log_hv_fd = -1;
 static evtchn_port_or_error_t log_hv_evtchn = -1;
 static xc_interface *xch; /* why does xenconsoled have two xc handles ? */
 static xc_evtchn *xce_handle = NULL;
+static xc_gnttab *xcg_handle = NULL;
 
 struct buffer {
        char *data;
@@ -501,6 +503,17 @@ static int xs_gather(struct xs_handle *xs, const char 
*dir, ...)
        va_end(ap);
        return ret;
 }
+
+static void domain_unmap_interface(struct domain *dom)
+{
+       if (dom->interface == NULL)
+               return;
+       if (xcg_handle && dom->ring_ref == -1)
+               xc_gnttab_munmap(xcg_handle, dom->interface, 1);
+       else
+               munmap(dom->interface, getpagesize());
+       dom->interface = NULL;
+}
  
 static int domain_create_ring(struct domain *dom)
 {
@@ -522,9 +535,19 @@ static int domain_create_ring(struct domain *dom)
        }
        free(type);
 
-       if (ring_ref != dom->ring_ref) {
-               if (dom->interface != NULL)
-                       munmap(dom->interface, getpagesize());
+       /* If using ring_ref and it has changed, remap */
+       if (ring_ref != dom->ring_ref && dom->ring_ref != -1)
+               domain_unmap_interface(dom);
+
+       if (!dom->interface && xcg_handle) {
+               /* Prefer using grant table */
+               dom->interface = xc_gnttab_map_grant_ref(xcg_handle,
+                       dom->domid, GNTTAB_RESERVED_CONSOLE,
+                       PROT_READ|PROT_WRITE);
+               dom->ring_ref = -1;
+       }
+       if (!dom->interface) {
+               /* Fall back to xc_map_foreign_range */
                dom->interface = xc_map_foreign_range(
                        xc, dom->domid, getpagesize(),
                        PROT_READ|PROT_WRITE,
@@ -720,9 +743,7 @@ static void shutdown_domain(struct domain *d)
 {
        d->is_dead = true;
        watch_domain(d, false);
-       if (d->interface != NULL)
-               munmap(d->interface, getpagesize());
-       d->interface = NULL;
+       domain_unmap_interface(d);
        if (d->xce_handle != NULL)
                xc_evtchn_close(d->xce_handle);
        d->xce_handle = NULL;
@@ -736,6 +757,13 @@ void enum_domains(void)
        xc_dominfo_t dominfo;
        struct domain *dom;
 
+       if (enum_pass == 0) {
+               xcg_handle = xc_gnttab_open(NULL, 0);
+               if (xcg_handle == NULL) {
+                       dolog(LOG_DEBUG, "Failed to open xcg handle: %d (%s)",
+                                 errno, strerror(errno));
+               }
+       }
        enum_pass++;
 
        while (xc_domain_getinfo(xc, domid, 1, &dominfo) == 1) {
@@ -946,6 +974,7 @@ void handle_io(void)
                              errno, strerror(errno));
                        goto out;
                }
+
                log_hv_fd = create_hv_log();
                if (log_hv_fd == -1)
                        goto out;
@@ -1097,6 +1126,10 @@ void handle_io(void)
                xc_evtchn_close(xce_handle);
                xce_handle = NULL;
        }
+       if (xcg_handle != NULL) {
+               xc_gnttab_close(xcg_handle);
+               xcg_handle = NULL;
+       }
        log_hv_evtchn = -1;
 }
 
-- 
1.7.11.7


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