blktap3: Introduce the tapback daemon (most of blkback in user-space).

diff -r fbf47a5d98ff -r 0777319f0a6e tools/blktap3/tapback/tapback.h
@@ -0,0 +1,253 @@
+/*
+ * 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__); \
+    }
+
+#define BUG_ON(_cond)       \
+    if (unlikely(_cond)) {  \
+        assert(0);          \
+    }
+
+/*
+ * XenStore path components.
+ *
+ * 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. 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    "xenio"
+#define BLKTAP3_BACKEND_PATH    XENSTORE_BACKEND"/"BLKTAP3_BACKEND_NAME
+#define BLKTAP3_BACKEND_TOKEN   XENSTORE_BACKEND"-"BLKTAP3_BACKEND_NAME
+#define BLKTAP3_FRONTEND_TOKEN  "otherend-state"
+#define BLKTAP3_SERIAL          BLKTAP3_BACKEND_NAME"-serial"
+
+/*
+ * 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;
+
+    /**
+     * TODO Supposed to solve some kind of race condition with libxl?
+     */
+    long long serial;
+
+    /**
+     * 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;
+
+    /**
+     * FIXME This is used but isn't initialised anywhere! This reflects
+     * tap_list.minor.
+     */
+    dev_t dev;
+
+    /**
+     * 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;
+
+} 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?
+     */
+    struct tqh_vbd devices;
+
+    /**
+     * For allocating serials.
+     */
+    long long serial;
+
+    /**
+     * TODO From xen/include/public/io/blkif.h: "The maximum supported size of
+     * the request ring buffer" 
+     */
+    int max_ring_page_order;
+};
+
+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.
+ *
+ * @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
+ *
+ * XXX Only called by tapback_read_watch.
+ */
+int
+tapback_backend_handle_backend_watch(char * const path);
+
+#endif /* __TAPBACK_H__ */

diff -r 0777319f0a6e -r efd3f343f7c7 tools/blktap3/tapback/xenstore.c
@@ -0,0 +1,188 @@
+/*
+ * 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.
+ */
+
+#include <stdarg.h>
+#include <stdio.h>
+#include <xenstore.h>
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "blktap3.h"
+#include "tapback.h"
+#include "xenstore.h"
+
+/**
+ * Prints the supplied arguments to a buffer and returns it. The buffer must
+ * be deallocated by the user.
+ */
+static char *
+vmprintf(const char * const fmt, va_list ap)
+{
+    char *s = NULL;
+
+    if (vasprintf(&s, fmt, ap) < 0)
+        s = NULL;
+
+    return s;
+}
+
+__printf(1, 2)
+char *
+mprintf(const char * const fmt, ...)
+{
+    va_list ap;
+    char *s = NULL;
+
+    va_start(ap, fmt);
+    s = vmprintf(fmt, ap);
+    va_end(ap);
+
+    return s;
+}
+
+char *
+tapback_xs_vread(struct xs_handle * const xs, xs_transaction_t xst,
+        const char * const fmt, va_list ap)
+{
+    char *path = NULL, *data = NULL;
+    unsigned int len = 0;
+
+    assert(xs);
+
+    path = vmprintf(fmt, ap);
+    data = xs_read(xs, xst, path, &len);
+    free(path);
+
+    return data;
+}
+
+__printf(3, 4)
+char *
+tapback_xs_read(struct xs_handle * const xs, xs_transaction_t xst,
+        const char * const fmt, ...)
+{
+    va_list ap;
+    char *s = NULL;
+
+    assert(xs);
+
+    va_start(ap, fmt);
+    s = tapback_xs_vread(xs, xst, fmt, ap);
+    va_end(ap);
+
+    return s;
+}
+
+char *
+tapback_device_read(const vbd_t * const device, const char * const path)
+{
+    assert(device);
+    assert(path);
+
+    return tapback_xs_read(blktap3_daemon.xs, blktap3_daemon.xst, "%s/%d/%s/%s",
+            BLKTAP3_BACKEND_PATH, device->domid, device->name, path);
+}
+
+char *
+tapback_device_read_otherend(vbd_t * const device,
+        const char * const path)
+{
+    assert(device);
+    assert(path);
+
+    return tapback_xs_read(blktap3_daemon.xs, blktap3_daemon.xst, "%s/%s",
+            device->frontend_path, path);
+}
+
+__scanf(3, 4)
+int
+tapback_device_scanf_otherend(vbd_t * const device,
+        const char * const path, const char * const fmt, ...)
+{
+    va_list ap;
+    int n = 0;
+    char *s = NULL;
+
+    assert(device);
+    assert(path);
+
+    if (!(s = tapback_device_read_otherend(device, path)))
+        return -1;
+    va_start(ap, fmt);
+    n = vsscanf(s, fmt, ap);
+    free(s);
+    va_end(ap);
+
+    return n;
+}
+
+__printf(4, 5)
+int
+tapback_device_printf(vbd_t * const device, const char * const key,
+        const bool mkread, const char * const fmt, ...)
+{
+    va_list ap;
+    int err = 0;
+    char *path = NULL, *val = NULL;
+    bool nerr = false;
+
+    assert(device);
+    assert(key);
+
+    if (!(path = mprintf("%s/%d/%s/%s", BLKTAP3_BACKEND_PATH, device->domid,
+                    device->name, key))) {
+        err = -errno;
+        goto fail;
+    }
+
+    va_start(ap, fmt);
+    val = vmprintf(fmt, ap);
+    va_end(ap);
+
+    if (!val) {
+        err = -errno;
+        goto fail;
+    }
+
+    if (!(nerr = xs_write(blktap3_daemon.xs, blktap3_daemon.xst, path, val,
+                    strlen(val)))) {
+        err = -errno;
+        goto fail;
+    }
+
+    if (mkread) {
+        struct xs_permissions perms = {
+            device->domid,
+            XS_PERM_READ
+        };
+
+        if (!(nerr = xs_set_permissions(blktap3_daemon.xs, blktap3_daemon.xst,
+                        path, &perms, 1))) {
+            err = -errno;
+            goto fail;
+        }
+    }
+
+fail:
+    free(path);
+    free(val);
+
+    return err;
+}

103 lines not on this page · raw message

diff -r efd3f343f7c7 -r a9beb303b541 tools/blktap3/tapback/log.c
@@ -0,0 +1,33 @@
+/*
+ * 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.
+ */
+
+#include "compiler.h"
+#include <stdarg.h>
+#include <syslog.h>
+
+void (*tapback_vlog) (int prio, const char *fmt, va_list ap) = vsyslog;
+
+__printf(2, 3) void
+tapback_log(int prio, const char *fmt, ...)
+{
+    va_list ap;
+    va_start(ap, fmt);
+    tapback_vlog(prio, fmt, ap);
+    va_end(ap);
+}

diff -r a9beb303b541 -r 8094db37a249 tools/blktap3/tapback/backend.c
@@ -0,0 +1,434 @@
+/*
+ * 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.
+ *
+ * This file contains the handler executed when the back-end XenStore path gets
+ * modified.
+ */
+
+#include "tapback.h"
+#include "xenstore.h"
+#include "tap-ctl-info.h"
+
+/**
+ * Removes the XenStore watch from the front-end.
+ *
+ * @param device the VBD whose front-end XenStore path should stop being
+ * watched
+ */
+static void
+tapback_device_unwatch_frontend_state(vbd_t * const device)
+{
+    assert(device);
+
+    if (device->frontend_state_path)
+        xs_unwatch(blktap3_daemon.xs, device->frontend_state_path,
+                BLKTAP3_FRONTEND_TOKEN);
+
+    free(device->frontend_state_path);
+    device->frontend_state_path = NULL;
+}
+
+/**
+ * Destroys and deallocates the back-end part of a VBD.
+ *
+ * @param device the VBD to destroy
+ */
+static void
+tapback_backend_destroy_device(vbd_t * const device)
+{
+    assert(device);
+
+    TAILQ_REMOVE(&blktap3_daemon.devices, device, backend_entry);
+
+    tapback_device_unwatch_frontend_state(device);
+
+    if (device->frontend_path) {
+        free(device->frontend_path);
+        device->frontend_path = NULL;
+    }
+
+    if (device->name) {
+        free(device->name);
+        device->name = NULL;
+    }
+
+    /*
+     * XXX device->bdev is expected to have been freed
+     */
+
+    free(device);
+}
+
+/**
+ * Retrieves the tapdisk designated to serve this device, storing this
+ * information in the supplied VBD handle.
+ *
+ * @param bdev the VBD handle for whose tapdisk handle should be retrieved
+ * @returns 0 on success, an error code otherwise
+ *
+ * FIXME How does this thing work since bdev->dev is never initialised?
+ * Probably because they're both initialised to 0 and we use one tapdisk per
+ * VBD?
+ *
+ * XXX Only called by blkback_probe.
+ */
+static inline int
+blkback_find_tapdisk(vbd_t * const bdev)
+{
+    struct tqh_tap_list list;
+    tap_list_t *tap = NULL;
+    int err = 0;
+
+    assert(bdev);
+
+    if ((err = tap_ctl_list(&list))) {
+        WARN("error listing tapdisks: %s\n", strerror(err));
+        return err;
+    }
+
+    err = ESRCH;    
+    if (!TAILQ_EMPTY(&list)) {
+        tap_list_for_each_entry(tap, &list)
+            if (tap->minor == minor(bdev->dev)) {
+                err = 0;
+                memcpy(&bdev->tap, tap, sizeof(bdev->tap));
+                break;
+            }
+        tap_ctl_list_free(&list);
+    } else
+        WARN("no tapdisks\n");
+
+    return err;
+}
+
+/**
+ * Creates a device and adds it to the list of devices.
+ * Initiates a XenStore watch to the front-end state.
+ *
+ * Creating the device implies initializing the handle and retrieving all the
+ * information of the tapdisk serving this VBD.
+ *
+ * @param domid the ID of the domain where the VBD is created
+ * @param name the name of the device
+ * @returns 0 on success, an error code otherwise
+ */
+static inline int
+tapback_backend_create_device(const domid_t domid, const char * const name)
+{
+    vbd_t *device = NULL;
+    int err = 0;
+    char *end = NULL;
+
+    assert(name);
+
+    DBG("creating device %d/%s\n", domid, name);
+
+    if (!(device = calloc(1, sizeof(*device)))) {
+        WARN("error allocating memory\n");
+        err = -errno;
+        goto fail;
+    }
+
+	/*
+	 * TODO replace with alloc_serial() and check for overflow
+	 */
+    device->serial = blktap3_daemon.serial++;
+    device->domid = domid;
+
+    TAILQ_INSERT_TAIL(&blktap3_daemon.devices, device, backend_entry);
+
+    if (!(device->name = strdup(name))) {
+        err = -errno;
+        goto fail;
+    }
+
+    /*
+     * Get the front-end path from XenStore. We need this to talk to front-end.
+     */
+    if (!(device->frontend_path = tapback_device_read(device, "frontend"))) {
+        err = -errno;
+        goto fail;
+    }
+
+    /*
+     * Write to XenStore tapback-serial.
+     */
+    if ((err = tapback_device_printf(device, BLKTAP3_SERIAL, false, "%lld",
+                    device->serial)))
+        goto fail;
+
+    /*
+     * Get the tapdisk that is serving this virtual block device, along with
+     * it's parameters.
+     */
+    device->devid = strtoul(name, &end, 0);
+    if (*end != 0 || end == name) {
+        err = -EINVAL;
+        goto fail;
+    }
+
+    if ((err = blkback_find_tapdisk(device))) {
+        WARN("error looking for tapdisk: %s", strerror(err));
+        goto fail;
+    }
+
+    /*
+     * get the VBD parameters from the tapdisk
+     */
+    if ((err = tap_ctl_info(device->tap.pid, device->tap.minor,
+                    &device->sectors, &device->sector_size, &device->info))) {
+        WARN("error retrieving disk characteristics: %s\n", strerror(err));
+        goto fail;
+    }
+
+    DBG("got %s-%d-%d with tapdev %d/%d\n", BLKTAP3_BACKEND_NAME,
+        device->domid, device->devid, device->tap.pid, device->tap.minor);
+
+	/*
+	 * Finally, watch the front-end path in XenStore for changes, i.e.
+     * /local/domain/<domid>/device/vbd/<devname>/state
+     * After this, we wait for the front-end to switch state to continue with
+     * the initialisation.
+	 */
+    if (!(device->frontend_state_path= mprintf("%s/state",
+                    device->frontend_path))) {
+        err = -errno;
+        goto fail;
+    }
+    /*
+     * We use the same token for all front-end watches. We don't have to use a
+     * unique token for each front-end watch because when a front-end watch
+     * fires we are given the XenStore path that changed.
+     */
+    if (!xs_watch(blktap3_daemon.xs, device->frontend_state_path,
+                BLKTAP3_FRONTEND_TOKEN)) {
+        free(device->frontend_state_path);
+        err = -errno;
+        goto fail;
+    }
+
+    return 0;
+
+fail:
+    WARN("error creating device: domid=%d name=%s err=%d (%s)\n",
+            domid, name, err, strerror(-err));
+    if (device)
+        tapback_backend_destroy_device(device);
+
+    return err;
+}
+
+/**
+ * Creates (removes) a device depending on the existence (non-existence) of the
+ * "backend/<backend name>/@domid/@devname" XenStore path.
+ *
+ * @param domid the ID of the domain where the VBD is created
+ * @param devname device name
+ * @returns 0 on success, an error code otherwise
+ */
+static int
+tapback_backend_probe_device(const domid_t domid, const char * const devname)
+{
+    int should_exist = 0, create = 0, remove = 0;
+    vbd_t *device = NULL;
+    char * s = NULL;
+
+    assert(devname);
+
+    DBG("probe device domid=%d name=%s\n", domid, devname);
+
+    /*
+     * Ask XenStore if the device _should_ exist.
+     */
+    s = tapback_xs_read(blktap3_daemon.xs, blktap3_daemon.xst, "%s/%d/%s",
+            BLKTAP3_BACKEND_PATH, domid, devname);
+    should_exist = s != NULL;
+    free(s);
+
+    /*
+     * Search the device list for this specific device.
+     */
+    tapback_backend_find_device(device,
+            device->domid == domid && !strcmp(device->name, devname));
+
+    /*
+	 * If XenStore says that the device should exist but it's not in our device 
+     * list, we must create it. If it's the other way round, this is a removal.
+     * If XenStore says that the device should exist and it's already in our
+     * device list, we must compare the serials in case the device got removed
+     * and re-created.
+     */
+    remove = device && !should_exist;
+    create = !device && should_exist;
+
+    DBG("should exist=%d device=%p remove=%d create=%d\n",
+        should_exist, device, remove, create);
+
+    /*
+     * The device exists in our list of device and XenStore says it should
+     * exist, we need to check if the device has been removed and re-added to
+     * XenStore. If this has happened the device's serial in XenStore will be
+     * different from the one in our list (sync with fast remove/re-create
+     * cycles).
+     */
+    if (device && should_exist) {
+        char *s = NULL;
+        long long serial = 0;
+
+        /*
+         * read the serial
+         */
+        if (!(s = tapback_device_read(device, BLKTAP3_SERIAL))) {
+            WARN("error reading serial for %s: %s\n", devname,
+                    strerror(errno));
+            return -errno;
+        }
+        serial = atoll(s);
+        free(s);
+
+        remove = create = serial != device->serial;
+
+        /*
+         * TODO Is it possible that neither create nor remove are true? If so,
+         * why was this function called in the first place?
+         */
+        WARN_ON(!remove && !create, "%d/%s neither created nor removed\n",
+                domid, devname);
+    }
+
+    /*
+     * Remember that remove and create may both be true at the same time, as
+     * this indicates that the device has been removed and re-created too fast.
+     * In this case, we too need to remove and re-create the device,
+     * respectively.
+     */
+
+    if (remove)
+        tapback_backend_destroy_device(device);
+
+    if (create) {
+        const int err = tapback_backend_create_device(domid, devname);
+        if (0 != err) {
+            WARN("error creating device %d on domain %d: %s\n", devname, domid,
+                    strerror(-err));
+            return err;
+        }
+    }
+
+    return 0;
+}
+
+/**
+ * Scans XenStore for all blktap3 devices and probes each one of them.
+ *
+ * XXX Only called by tapback_backend_handle_backend_watch.
+ */
+static int
+tapback_backend_scan(void)
+{
+    vbd_t *device = NULL, *next = NULL;
+    unsigned int i = 0, j = 0, n = 0, m = 0;
+    char **dir = NULL;
+
+    /*
+     * scrap all non-existent devices
+     * FIXME Why do we do this?
+     * FIXME Is this costly?
+     */
+
+    tapback_backend_for_each_device(device, next)
+        tapback_backend_probe_device(device->domid, device->name);
+
+    /*
+     * probe the new ones
+     *
+     * FIXME We're checking each and every device in each and every domain,
+     * could there be a performance issue in the presence of many VMs/VBDs?
+     * (e.g. boot-storm)
+     */
+    if (!(dir = xs_directory(blktap3_daemon.xs, blktap3_daemon.xst,
+                    BLKTAP3_BACKEND_PATH, &n)))
+        return 0;
+
+    for (i = 0; i < n; i++) { /* for each domain */
+        char *path = NULL, **sub = NULL, *end = NULL;
+        domid_t domid = 0;
+
+        /*
+         * Get the domain ID.
+         */
+        domid = strtoul(dir[i], &end, 0);
+        if (*end != 0 || end == dir[i])
+            continue;
+
+        /*
+         * Read the devices of this domain.
+         */
+        path = mprintf("%s/%d", BLKTAP3_BACKEND_PATH, domid);
+        assert(path != NULL);
+        sub = xs_directory(blktap3_daemon.xs, blktap3_daemon.xst, path, &m);
+        free(path);
+
+        /*
+         * Probe each device.
+         */
+        for (j = 0; j < m; j++)
+            tapback_backend_probe_device(domid, sub[j]);
+
+        free(sub);
+    }
+
+    free(dir);
+    return 0;
+}
+
+int
+tapback_backend_handle_backend_watch(char * const path)
+{
+    char *s = NULL, *end = NULL, *name = NULL;
+    domid_t domid = 0;
+
+    assert(path);
+
+    s = strtok(path, "/");
+    assert(!strcmp(s, XENSTORE_BACKEND));
+    if (!(s = strtok(NULL, "/")))
+        return tapback_backend_scan();
+
+    assert(!strcmp(s, BLKTAP3_BACKEND_NAME));
+    if (!(s = strtok(NULL, "/")))
+        return tapback_backend_scan();
+
+    domid = strtoul(s, &end, 0);
+    if (*end != 0 || end == s) {
+        WARN("invalid domain ID \'%s\'\n", s);
+        return -EINVAL;
+    }
+
+    /*
+     * FIXME since we know which domain changed, why scan the whole thing?
+     * Add the domid as an optional parameter to tapback_backend_scan.
+     */
+    if (!(name = strtok(NULL, "/")))
+        return tapback_backend_scan();
+
+    /*
+     * Create or remove a specific device.
+     */
+    return tapback_backend_probe_device(domid, name);
+}

diff -r 8094db37a249 -r d332adcebe40 tools/blktap3/include/blktap3.h
@@ -44,4 +44,19 @@
 	TAILQ_REMOVE(src, node, entry);				\
 	TAILQ_INSERT_TAIL(dst, node, entry);
 
+/**
+ * Block I/O protocol
+ *
+ * Taken from linux/drivers/block/xen-blkback/common.h so that blkfront can
+ * work both with blktap2 and blktap3.
+ *
+ * TODO linux/drivers/block/xen-blkback/common.h contains other definitions
+ * necessary for allowing tapdisk3 to talk directly to blkfront. Find a way to
+ * use the definitions from there.
+ */
+enum blkif_protocol {
+       BLKIF_PROTOCOL_NATIVE = 1,
+       BLKIF_PROTOCOL_X86_32 = 2,
+       BLKIF_PROTOCOL_X86_64 = 3,
+};
 #endif /* __BLKTAP_3_H__ */

396 lines not on this page · raw message

diff -r d332adcebe40 -r 407ebde55295 tools/blktap3/tapback/tapback.c
@@ -0,0 +1,286 @@
+/*
+ * 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.
+ *
+ * This file contains the core of the tapback daemon, the user space daemon
+ * that acts as a device's back-end.
+ */
+
+/* 
+ * TODO Some of these includes may be useless.
+ * TODO Replace hard-coding strings with defines/const string.
+ */
+#include <stdlib.h>
+#include <stdarg.h>
+#include <assert.h>
+#include <syslog.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <libgen.h>
+#include <getopt.h>
+#include <sys/ioctl.h>
+#include <sys/mount.h>
+#include <syslog.h>
+
+#include "blktap3.h"
+#include "stdio.h" /* TODO tap-ctl.h needs to include stdio.h */
+#include "tap-ctl.h"
+#include "tapback.h"
+
+void tapback_log(int prio, const char *fmt, ...);
+void (*tapback_vlog) (int prio, const char *fmt, va_list ap);
+
+struct _blktap3_daemon blktap3_daemon;
+
+/**
+ * Read changes that occurred on the "backend/<backend name>" XenStore path
+ * or one of the front-end paths and act accordingly.
+ */
+static inline void
+tapback_read_watch(void)
+{
+    char **watch = NULL, *path = NULL, *token = NULL;
+    unsigned int n = 0;
+    int err = 0, _abort = 0;
+
+    /* read the change */
+    watch = xs_read_watch(blktap3_daemon.xs, &n);
+    path = watch[XS_WATCH_PATH];
+    token = watch[XS_WATCH_TOKEN];
+
+    /*
+     * TODO Put the body of "again:" into a loop instead of using goto.
+     */
+again:
+    if (!(blktap3_daemon.xst = xs_transaction_start(blktap3_daemon.xs))) {
+        WARN("error starting transaction\n");
+        goto fail;
+    }
+
+    /*
+     * The token indicates which XenStore watch triggered, the front-end one or
+     * the back-end one.
+     */
+    if (!strcmp(token, BLKTAP3_FRONTEND_TOKEN)) 
+        err = tapback_backend_handle_otherend_watch(path);
+    else if (!strcmp(token, BLKTAP3_BACKEND_TOKEN))
+        /*
+         * TODO The XenStore watch may trigger for a not yet
+         * discovered/understood reason.  The result is
+         * tapback_backend_handle_backend_watch not doing anything interesting,
+         * it only checks the 'tapback-serial'.
+         */
+        err = tapback_backend_handle_backend_watch(path);
+    else {
+        WARN("invalid token \'%s\'\n", token);
+        err = EINVAL;
+    }
+
+    _abort = !!err;
+    if (_abort)
+        DBG("aborting transaction: %s\n", strerror(-err));
+
+    err = xs_transaction_end(blktap3_daemon.xs, blktap3_daemon.xst, _abort);
+    blktap3_daemon.xst = 0;
+    if (!err) {
+        err = -errno;
+        /*
+         * This is OK according to xs_transaction_end's semantics.
+         */
+        if (EAGAIN == errno)
+            goto again;
+        DBG("error ending transaction: %s\n", strerror(err));
+    }
+
+fail:
+    free(watch);
+    return;
+}
+
+static void
+tapback_backend_destroy(void)
+{
+    if (blktap3_daemon.xs) {
+        xs_daemon_close(blktap3_daemon.xs);
+        blktap3_daemon.xs = NULL;
+    }
+}
+
+/**
+ * Initializes the back-end descriptor. There is one back-end per tapback
+ * process. Also, it initiates a watch to XenStore on backend/<backend name>.
+ *
+ * @returns 0 on success, an error code otherwise
+ */
+static inline int
+tapback_backend_create(void)
+{
+    int err = -EINVAL;    
+
+    TAILQ_INIT(&blktap3_daemon.devices);
+    blktap3_daemon.xst = XBT_NULL;
+
+    if (!(blktap3_daemon.xs = xs_daemon_open())) {
+        err = -EINVAL;
+        goto fail;
+    }
+
+    /*
+     * Watch the back-end.
+     */
+    if (!xs_watch(blktap3_daemon.xs, BLKTAP3_BACKEND_PATH,
+                BLKTAP3_BACKEND_TOKEN)) {
+        err = -errno;
+        goto fail;
+    }
+
+    return 0;
+
+fail:
+	tapback_backend_destroy();
+
+    return -err;
+}
+
+/**
+ * Runs the daemon.
+ *
+ * Watches backend/<backend name> and the front-end devices.
+ */
+static inline int
+tapback_backend_run(void)
+{
+    const int fd = xs_fileno(blktap3_daemon.xs);
+	int err;
+
+    do {
+        fd_set rfds;
+        int nfds = 0;
+
+        FD_ZERO(&rfds);
+        FD_SET(fd, &rfds);
+
+        /* poll the fd for changes in the XenStore path we're interested in */
+        if ((nfds = select(fd + 1, &rfds, NULL, NULL, NULL)) < 0) {
+            perror("error monitoring XenStore");
+            err = -errno;
+            break;
+        }
+
+        if (FD_ISSET(fd, &rfds))
+            tapback_read_watch();
+    } while (1);
+
+    return err;
+}
+
+static char *blkback_ident;
+
+static void
+blkback_vlog_fprintf(const int prio, const char * const fmt, va_list ap)
+{
+    const char *strprio[] = {
+        [LOG_DEBUG] = "DBG",
+        [LOG_INFO] = "INF",
+        [LOG_WARNING] = "WRN"
+    };
+
+    assert(prio >= 0);
+    BUG_ON(prio > sizeof(strprio) / sizeof(strprio[0]));
+    BUG_ON(!strprio[prio]);
+
+    fprintf(stderr, "%s[%s] ", blkback_ident, strprio[prio]);
+    vfprintf(stderr, fmt, ap);
+}
+
+/**
+ * Print tapback's usage instructions.
+ */
+static void
+usage(FILE * const stream, const char * const prog)
+{
+    assert(stream);
+    assert(prog);
+
+    fprintf(stream,
+            "usage: %s\n"
+            "\t[-D|--debug]\n"
+			"\t[-h|--help]\n", prog);
+}
+
+int main(int argc, char **argv)
+{
+    const char *prog = NULL;
+    int opt_debug = 0;
+    int err = 0;
+
+    prog = basename(argv[0]);
+
+    opt_debug = 0;
+
+    do {
+        const struct option longopts[] = {
+            {"help", 0, NULL, 'h'},
+            {"debug", 0, NULL, 'D'},
+        };
+        int c;
+
+        c = getopt_long(argc, argv, "h:D", longopts, NULL);
+        if (c < 0)
+            break;
+
+        switch (c) {
+        case 'h':
+            usage(stdout, prog);
+            return 0;
+        case 'D':
+            opt_debug = 1;
+            break;
+        case '?':
+            goto usage;
+        }
+    } while (1);
+
+    blkback_ident = BLKTAP3_BACKEND_TOKEN;
+    if (opt_debug)
+        tapback_vlog = blkback_vlog_fprintf;
+    else
+        openlog(blkback_ident, 0, LOG_DAEMON);
+
+    if (!opt_debug) {
+        if ((err = daemon(0, 0))) {
+            err = -errno;
+            goto fail;
+        }
+    }
+
+	if ((err = tapback_backend_create())) {
+        WARN("error creating blkback: %s\n", strerror(err));
+        goto fail;
+    }
+
+    err = tapback_backend_run();
+
+    tapback_backend_destroy();
+
+fail:
+    return err ? -err : 0;
+
+usage:
+    usage(stderr, prog);
+    return 1;
+}