[Xen-devel] [PATCH 1 of 7 v5] blktap3/tapback: Introduce core defines and structure definitions

[Thanos Makatos <thanos.makatos@xxxxxxxxxx>]

Signed-off-by: Thanos Makatos <thanos.makatos@xxxxxxxxxx>

---
Changed since v2:
  * Removed BUG_ON macro.
  * Fixed whitespace in tapback_backend_find_device.
  * Clarified back-end name (xenio).
  * Removed references to the "serial" thing.
  * Remove unused member dev from struct vbd.
  * Introduce prototype of function XenbusState2str.

Changed since v3:
  * Use vbd3 as the back-end name, as this allows blktap2 and blktap3 to
    co-exist.
  * struct vbd now carries the type:/path/to/file as it is later used to tell
    the tapdisk which VBD must be connected to the sring.

Changed since v4:
  * Minor documentation.

diff --git a/tools/blktap3/tapback/tapback.h b/tools/blktap3/tapback/tapback.h
new file mode 100644
--- /dev/null
+++ b/tools/blktap3/tapback/tapback.h
@@ -0,0 +1,283 @@
+/*
+ * Copyright (C) 2012      Citrix Ltd.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
+ * USA.
+ */
+
+#ifndef __TAPBACK_H__
+#define __TAPBACK_H__
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <assert.h>
+#include <string.h>
+
+#include <xen/xen.h>
+#include <xenstore.h>
+#include <xen/io/xenbus.h>
+#include <xen/event_channel.h>
+#include <xen/grant_table.h>
+
+#include "tap-ctl.h"
+
+void tapback_log(int prio, const char *fmt, ...);
+void (*tapback_vlog) (int prio, const char *fmt, va_list ap);
+
+#define DBG(_fmt, _args...)  tapback_log(LOG_DEBUG, "%s:%d "_fmt, __FILE__, \
+        __LINE__, ##_args)
+#define INFO(_fmt, _args...) tapback_log(LOG_INFO, _fmt, ##_args)
+#define WARN(_fmt, _args...) tapback_log(LOG_WARNING, "%s:%d "_fmt, __FILE__, \
+        __LINE__, ##_args)
+
+#define WARN_ON(_cond, fmt, ...)    \
+    if (unlikely(_cond)) {          \
+        printf(fmt, ##__VA_ARGS__); \
+    }
+
+/*
+ * Pre-defined XenStore path components used for running the XenBus protocol.
+ *
+ * To avoid confusion with blktap2, we'll use a new kind of device for libxl
+ * defining it in tools/libxl/libxl_types_internal.idl. This will be done by
+ * the patch that adds libxl support for blktap3. The temporary back-end name
+ * is "xenio". Once blktap3 becomes the default back-end, its back-end name
+ * should be "vbd" and "xenio" will be removed. TODO When that patch is sent,
+ * use the definition from there instead of hard-coding it here.
+ */
+#define XENSTORE_BACKEND        "backend"
+#define BLKTAP3_BACKEND_NAME    "vbd3"
+#define BLKTAP3_BACKEND_PATH    XENSTORE_BACKEND"/"BLKTAP3_BACKEND_NAME
+#define BLKTAP3_BACKEND_TOKEN   XENSTORE_BACKEND"-"BLKTAP3_BACKEND_NAME
+#define BLKTAP3_FRONTEND_TOKEN  "otherend-state"
+
+/*
+ * TODO Put the rest of the front-end nodes defined in blkif.h here and group
+ * them. e.g. FRONTEND_NODE_xxx.
+ */
+#define RING_REF                "ring-ref"
+#define FEAT_PERSIST            "feature-persistent"
+
+/**
+ * A Virtual Block Device (VBD), represents a block device in a guest VM.
+ * Contains all relevant information.
+ */
+typedef struct vbd {
+
+    /**
+     * Device name, as retrieved from XenStore at probe-time.
+     */
+    char *name;
+
+    /**
+     * The device ID. Same as vbd.name, we keep it around because the tapdisk
+     * control libreary wants it as an int and not as a string.
+     */
+    int devid;
+
+    /**
+     * For linked lists.
+     */
+     TAILQ_ENTRY(vbd) backend_entry;
+
+    /**
+     * The domain ID this VBD belongs to.
+     */
+    domid_t domid;
+
+    /**
+     * The root directory in XenStore for this VBD. This is where all
+     * directories and key/value pairs related to this VBD are stored.
+     */
+    char *frontend_path;
+
+    /**
+     * XenStore path to the VBD's state. This is just
+     * vbd.frontend_path + "/state", we keep it around so we don't have to
+     * allocate/free memory all the time.
+     */
+    char *frontend_state_path;
+
+    /**
+     * Indicates whether the tapdisk is connected to the shared ring.
+     */
+    bool connected;
+
+    /**
+     * Descriptor of the tapdisk process serving this virtual block device. We
+     * need this until the end of the VBD's lifetime in order to disconnect
+     * the tapdisk from the shared ring.
+     */
+    tap_list_t tap;
+
+    /*
+     * XXX We keep sector_size, sectors, and info because we need to
+     * communicate them to the front-end not only when the front-end goes to
+     * XenbusStateInitialised, but to XenbusStateConnected as well.
+     */
+
+    /**
+     * Sector size, supplied by the tapdisk, communicated to blkfront.
+     */
+    unsigned int sector_size;
+
+    /**
+     * Number of sectors, supplied by the tapdisk, communicated to blkfront.
+     */
+    unsigned long long sectors;
+
+    /**
+     * VDISK_???, defined in include/xen/interface/io/blkif.h.
+     */
+    unsigned int info;
+
+    /**
+     * type:/path/to/file
+     */
+    char *params;
+
+    /**
+     * /path/to/file
+     */
+    char *path;
+
+    /**
+     * type (vhd, aio, etc.)
+     */
+    char *type;
+
+} vbd_t;
+
+TAILQ_HEAD(tqh_vbd, vbd);
+
+/**
+ * The collection of all necessary handles and descriptors.
+ */
+struct _blktap3_daemon {
+
+    /**
+     * A handle to XenStore.
+     */
+    struct xs_handle *xs;
+
+    /**
+     * For executing transacted operations on XenStore.
+     */
+    xs_transaction_t xst;
+
+    /**
+     * The list of virtual block devices.
+     *
+     * TODO We sometimes have to scan the whole list to find the device/domain
+     * we're interested in, should we optimize this? E.g. use a hash table
+     * for O(1) access?
+     * TODO Replace with a hash table (hcreate etc.)?
+     */
+    struct tqh_vbd devices;
+
+    /**
+     * TODO From xen/include/public/io/blkif.h: "The maximum supported size of
+     * the request ring buffer"
+     */
+    int max_ring_page_order;
+
+    /**
+     * Unix domain socket for controlling the daemon.
+     */
+    int ctrl_sock;
+};
+
+extern struct _blktap3_daemon blktap3_daemon;
+
+#define tapback_backend_for_each_device(_device, _next)        \
+       TAILQ_FOREACH_SAFE(_device, &blktap3_daemon.devices, backend_entry, 
_next)
+
+/**
+ * Iterates over all devices and returns the one for which the condition is
+ * true.
+ */
+#define tapback_backend_find_device(_device, _cond)     \
+do {                                                    \
+    vbd_t *__next;                                      \
+    int found = 0;                                      \
+    tapback_backend_for_each_device(_device, __next) {  \
+        if (_cond) {                                    \
+            found = 1;                                  \
+            break;                                      \
+        }                                               \
+    }                                                   \
+    if (!found)                                         \
+        _device = NULL;                                 \
+} while (0)
+
+/**
+ * Act in response to a change in the front-end XenStore path.
+ *
+ * TODO We only care about changes on the front-end's state. Document this.
+ * Also, executed the body of this function (blkback_frontend_changed) iff a
+ * change occured on the state, otherwise immediatelly return.
+ *
+ * @param path the front-end's XenStore path that changed
+ * @returns 0 on success, an error code otherwise
+ *
+ * XXX Only called by tapback_read_watch
+ */
+int
+tapback_backend_handle_otherend_watch(const char * const path);
+
+/**
+ * Act in response to a change in the back-end directory in XenStore.
+ *
+ * If the path is "/backend" or "/backend/<backend name>", all devices are
+ * probed. Otherwise, the path should be
+ * "backend/<backend name>/<domid>/<device name>"
+ * (i.e. backend/<backend name>/1/51712), and in this case this specific device
+ * is probed.
+ *
+ * @param path the back-end's XenStore path that changed @returns 0 on success,
+ * an error code otherwise
+ *
+ * TODO We only care about changes on the domid/devid component, as this
+ * signifies device creation/removal. Changes to paths such as
+ * "backend/vbd3/29/51712/mode" or "backend/vbd3/29/51712/removable" are
+ * currently uninteresting and we shouldn't do anything.
+ *
+ * XXX Only called by tapback_read_watch.
+ */
+int
+tapback_backend_handle_backend_watch(char * const path);
+
+/**
+ * Converts XenbusState values to a printable string, e.g. XenbusStateConnected
+ * corresponds to "connected".
+ *
+ * @param xbs the XenbusState to convert
+ * @returns a printable string
+ */
+char *
+XenbusState2str(const XenbusState xbs);
+
+/**
+ * Converts XenbusState values to a printable string, e.g. XenbusStateConnected
+ * corresponds to "connected".
+ *
+ * @param xbs the XenbusState to convert
+ * @returns a printable string
+ */
+char *
+XenbusState2str(const XenbusState xbs);
+
+#endif /* __TAPBACK_H__ */

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