tools/xl: support new 9pfs backend xen_9pfsd

Add support for the new 9pfs backend "xen_9pfsd". For this backend type
the tag defaults to "Xen" and the host side path to
"/var/log/xen/guests/<dom-name>".

Do most of the default settings in libxl. Unfortunately the default
path can't easily be set in libxl, as the domain name isn't available
in the related 9pfs specific function.

Settings the defaults in libxl requires to move the sanity checking
of 9pfs parameters from xl to libxl, too.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jason Andryuk <jandryuk@gmail.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>

docs/man/xl.cfg.5.pod.in

@@ -772,10 +772,16 @@ settings, from the following list:
 
 =over 4
 
+=item B<type=TYPE>
+
+The backendtype for the PV device. Supported values are B<qemu> and
+B<xen_9pfsd>.  The default is B<qemu>.
+
 =item B<tag=STRING>
 
 9pfs tag to identify the filesystem share. The tag is needed on the
-guest side to mount it.
+guest side to mount it. For the backendtype of B<xen_9pfsd> the tag defaults to
+"Xen".
 
 =item B<security_model="none">
 
@@ -785,12 +791,38 @@ squash or remap).
 
 =item B<path=STRING>
 
-Filesystem path on the backend to export.
+Filesystem path on the backend to export. For the backendtype of B<xen_9pfsd>
+the path defaults to "@XEN_LOG_DIR@/guests/<guest-name>".
 
 =item B<backend=domain-id>
 
 Specify the backend domain name or id, defaults to dom0.
 
+=item B<max-files=NUMBER>
+
+Specify the maximum number of files below B<path>. A value of 0 (which
+is the default) doesn't limit the number of files. Only valid for
+B<type=xen_9pfsd>.
+
+=item B<max-open-files=NUMBER>
+
+Specify the maximum number of concurrently opened files below B<path>.
+Multiple opens of the same file are counted individually. Only valid for
+B<type=xen_9pfsd>, which has a default of B<max-open-files=5>.
+
+=item B<max-space=NUMBER>
+
+Specify the maximum used disk space in MiB below B<path>. A value of 0 (which
+is the default) doesn't limit the usable disk space. Only valid for
+B<type=xen_9pfsd>.
+
+=item B<auto-delete=BOOLEAN>
+
+When set the backend will delete the oldest file which is currently not
+opened by the guest in case the disk space limit set via B<max-space> or the
+file limit set via B<max-files> is being reached. Only valid for
+B<type=xen_9pfsd>.
+
 =back
 
 =item B<pvcalls=[ "backend=domain-id", ... ]>

tools/libs/light/libxl_9pfs.c

@@ -20,6 +20,24 @@
 static int libxl__device_p9_setdefault(libxl__gc *gc, uint32_t domid,
                                        libxl_device_p9 *p9, bool hotplug)
 {
+    if (p9->type == LIBXL_P9_TYPE_UNKNOWN) {
+        p9->type = LIBXL_P9_TYPE_QEMU;
+    }
+    if (p9->type == LIBXL_P9_TYPE_QEMU &&
+        (p9->max_files || p9->max_open_files || p9->max_space ||
+         p9->auto_delete)) {
+        LOGD(ERROR, domid, "Illegal 9pfs parameter combination");
+        return ERROR_INVAL;
+    }
+    if (p9->type == LIBXL_P9_TYPE_XEN_9PFSD && !p9->tag) {
+        p9->tag = libxl__strdup(NOGC, "Xen");
+    }
+
+    if (!p9->path || !p9->security_model || !p9->tag) {
+        LOGD(ERROR, domid, "9pfs spec missing required field!");
+        return ERROR_INVAL;
+    }
+
     return libxl__resolve_domid(gc, p9->backend_domname, &p9->backend_domid);
 }
 

tools/xl/xl_parse.c

@@ -2233,6 +2233,20 @@ void parse_config_data(const char *config_source,
                     replace_string(&p9->tag, value);
                 } else if (!strcmp(key, "backend")) {
                     replace_string(&p9->backend_domname, value);
+                } else if (!strcmp(key, "type")) {
+                    if (libxl_p9_type_from_string(value, &p9->type)) {
+                        fprintf(stderr, "failed to parse 9pfs type: %s\n",
+                                value);
+                        exit(1);
+                    }
+                } else if (!strcmp(key, "max-files")) {
+                    p9->max_files = parse_ulong(value);
+                } else if (!strcmp(key, "max-open-files")) {
+                    p9->max_open_files = parse_ulong(value);
+                } else if (!strcmp(key, "max-space")) {
+                    p9->max_space = parse_ulong(value);
+                } else if (!strcmp(key, "auto-delete")) {
+                    p9->auto_delete = strtoul(value, NULL, 0);
                 } else {
                     fprintf(stderr, "Unknown 9pfs parameter '%s'\n", key);
                     exit(1);
@@ -2243,9 +2257,12 @@ void parse_config_data(const char *config_source,
 
             libxl_string_list_dispose(&pairs);
 
-            if (!p9->path || !p9->security_model || !p9->tag) {
-                fprintf(stderr, "9pfs spec missing required field!\n");
-                exit(1);
+            if (p9->type == LIBXL_P9_TYPE_XEN_9PFSD && !p9->path) {
+                char *path;
+
+                xasprintf(&path, XEN_LOG_DIR "/guests/%s", c_info->name);
+                replace_string(&p9->path, path);
+                free(path);
             }
         }
     }