xen_console: support the new extended xenstore protocol

Since CS 21994 on xen-unstable.hg and CS
466608f3a32e1f9808acdf832a5843af37e5fcec on qemu-xen-unstable.git, few
changes have been introduced to the PV console xenstore protocol, as
described by the document docs/misc/console.txt under xen-unstable.hg.

From the Qemu point of view, very few modifications are needed to
correctly support the protocol: read from xenstore the "output" node
that tell us what the output of the PV console is going to be.
In case the output is a tty, write to xenstore the device name.

Changes in v2:

- fix error paths: free malloc'ed strings and close the xenstore
connection before returning;

- remove useless snprintf in xenstore_store_pv_console_info if i == 0.

Changes in v3:

- replace xs_daemon_open/xs_daemon_close with xs_open/xs_close.

Changes in v4:

- add a compatibility implementation of xs_open/xs_close.

Changes in v5:

- fix code style.

[agraf] fix build error due to missing stub

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Alexander Graf <agraf@suse.de>

xen-all.c

@@ -737,6 +737,66 @@ static void cpu_handle_ioreq(void *opaque)
     }
 }
 
+static int store_dev_info(int domid, CharDriverState *cs, const char *string)
+{
+    struct xs_handle *xs = NULL;
+    char *path = NULL;
+    char *newpath = NULL;
+    char *pts = NULL;
+    int ret = -1;
+
+    /* Only continue if we're talking to a pty. */
+    if (strncmp(cs->filename, "pty:", 4)) {
+        return 0;
+    }
+    pts = cs->filename + 4;
+
+    /* We now have everything we need to set the xenstore entry. */
+    xs = xs_open(0);
+    if (xs == NULL) {
+        fprintf(stderr, "Could not contact XenStore\n");
+        goto out;
+    }
+
+    path = xs_get_domain_path(xs, domid);
+    if (path == NULL) {
+        fprintf(stderr, "xs_get_domain_path() error\n");
+        goto out;
+    }
+    newpath = realloc(path, (strlen(path) + strlen(string) +
+                strlen("/tty") + 1));
+    if (newpath == NULL) {
+        fprintf(stderr, "realloc error\n");
+        goto out;
+    }
+    path = newpath;
+
+    strcat(path, string);
+    strcat(path, "/tty");
+    if (!xs_write(xs, XBT_NULL, path, pts, strlen(pts))) {
+        fprintf(stderr, "xs_write for '%s' fail", string);
+        goto out;
+    }
+    ret = 0;
+
+out:
+    free(path);
+    xs_close(xs);
+
+    return ret;
+}
+
+void xenstore_store_pv_console_info(int i, CharDriverState *chr)
+{
+    if (i == 0) {
+        store_dev_info(xen_domid, chr, "/console");
+    } else {
+        char buf[32];
+        snprintf(buf, sizeof(buf), "/device/console/%d", i);
+        store_dev_info(xen_domid, chr, buf);
+    }
+}
+
 static void xenstore_record_dm_state(XenIOState *s, const char *state)
 {
     char path[50];