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[libvirt] [PATCH RFC] Add domainSave/Restore to lib xl driver



This patch adds save/restore functionality to the libxl driver.

It is a v2 of this patch:
https://www.redhat.com/archives/libvir-list/2011-April/msg00338.html

v2:
* header is now padded and has a version field
* the correct restore function from libxl is used
* only create the restore event once in libxlVmStart


However I ran into a reproducible segfault.
Assume you saved a vm with:
# virsh save domU foo.img

If you restore the save image,
destroy the vm and restore it again, a segfault occurs:
# virsh restore foo.img
# virsh destroy domU
# virsh restore foo.img
# segfault

If you restart libvirt between the restores no segfault occurs:
# virsh restore foo.img
# virsh destroy domU
# restart libvirt
# virsh restore foo.img

According to a gdb backtrace a memcpy from the function xc_domain_restore
is causing the segfault.
Then I saved a vm with the xl tool (which also uses the libxenlight interface)
and restored it twice. No segfault occured.

So I figured something must went wrong in libvirt.
However I was unable to identify the responsible part of code.
Now I am hoping that a review will possibly solve this issue.


Here is the gdb backtrace:
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x42ba1950 (LWP 23813)]
0x00007f1bc17d906b in memcpy () from /lib/libc.so.6
(gdb) bt
#0  0x00007f1bc17d906b in memcpy () from /lib/libc.so.6
#1  0x00007f1bc2b49346 in xc_domain_restore () from /usr/lib/libxenguest.so.4.0
#2  0x00007f1bc31a80f3 in ?? () from /usr/lib/libxenlight.so.1.0
#3  0x00007f1bc31a105e in ?? () from /usr/lib/libxenlight.so.1.0
#4  0x000000000049389a in libxlVmStart (driver=0x7f1bb8003e80, vm=0x7f1bb8053400, start_paused=false, restore_fd=20) at libxl/libxl_driver.c:531
#5  0x00000000004945c5 in libxlDomainRestore (conn=<value optimized out>, from=<value optimized out>) at libxl/libxl_driver.c:1745
#6  0x00007f1bc1f85a4b in virDomainRestore (conn=0x20a4d40, from=0x7f1bb804d260 "/root/tt.img") at libvirt.c:2330
#7  0x000000000042c5b8 in remoteDispatchDomainRestore (server=<value optimized out>, client=<value optimized out>, conn=0xaf0, hdr=<value optimized out>, rerr=0x42ba0e20,
    args=0xffffffff, ret=0x42ba0f00) at remote.c:2616
#8  0x0000000000431cb7 in remoteDispatchClientRequest (server=0x209fe90, client=0x20a4ad0, msg=0x20b1aa0) at dispatch.c:524
#9  0x000000000041dd53 in qemudWorker (data=0x20a8018) at libvirtd.c:1622
#10 0x00007f1bc1cb9fc7 in start_thread () from /lib/libpthread.so.0
#11 0x00007f1bc182b64d in clone () from /lib/libc.so.6
#12 0x0000000000000000 in ?? ()


Cheers,
Markus

---
 src/libxl/libxl_conf.h   |   14 +++
 src/libxl/libxl_driver.c |  228 ++++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 225 insertions(+), 17 deletions(-)

diff --git a/src/libxl/libxl_conf.h b/src/libxl/libxl_conf.h
index 8c87786..e7dd3a1 100644
--- a/src/libxl/libxl_conf.h
+++ b/src/libxl/libxl_conf.h
@@ -1,5 +1,6 @@
 /*---------------------------------------------------------------------------*/
 /*  Copyright (c) 2011 SUSE LINUX Products GmbH, Nuernberg, Germany.
+ *  Copyright (C) 2011 Univention GmbH.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -17,6 +18,7 @@
  *
  * Authors:
  *     Jim Fehlig <jfehlig novell com>
+ *     Markus Groß <gross univention de>
  */
 /*---------------------------------------------------------------------------*/

@@ -85,6 +87,18 @@ struct _libxlDomainObjPrivate {
     int eventHdl;
 };

+#define LIBXL_SAVE_MAGIC "libvirt-xml\n \0 \r"
+#define LIBXL_SAVE_VERSION 1
+
+typedef struct _libxlSavefileHeader libxlSavefileHeader;
+typedef libxlSavefileHeader *libxlSavefileHeaderPtr;
+struct _libxlSavefileHeader {
+    char magic[sizeof(LIBXL_SAVE_MAGIC)-1];
+    uint32_t version;
+    uint32_t xmlLen;
+    /* 24 bytes used, pad up to 64 bytes */
+    uint32_t unused[10];
+};

 # define libxlError(code, ...)                                     \
     virReportErrorHelper(VIR_FROM_LIBXL, code, __FILE__,           \
diff --git a/src/libxl/libxl_driver.c b/src/libxl/libxl_driver.c
index 247d78e..56a62c9 100644
--- a/src/libxl/libxl_driver.c
+++ b/src/libxl/libxl_driver.c
@@ -29,6 +29,7 @@
 #include <sys/utsname.h>
 #include <math.h>
 #include <libxl.h>
+#include <fcntl.h>

 #include "internal.h"
 #include "logging.h"
@@ -60,11 +61,10 @@

 static libxlDriverPrivatePtr libxl_driver = NULL;

-
 /* Function declarations */
 static int
-libxlVmStart(libxlDriverPrivatePtr driver,
-             virDomainObjPtr vm, bool start_paused);
+libxlVmStart(libxlDriverPrivatePtr driver, virDomainObjPtr vm,
+             bool start_paused, int restore_fd);


 /* Function definitions */
@@ -188,7 +188,7 @@ libxlAutostartDomain(void *payload, const void *name ATTRIBUTE_UNUSED,
     virResetLastError();

     if (vm->autostart && !virDomainObjIsActive(vm) &&
-        libxlVmStart(driver, vm, false) < 0) {
+        libxlVmStart(driver, vm, false, -1) < 0) {
         err = virGetLastError();
         VIR_ERROR(_("Failed to autostart VM '%s': %s"),
                   vm->def->name,
@@ -378,7 +378,7 @@ static void libxlEventHandler(int watch,
                 break;
             case SHUTDOWN_reboot:
                 libxlVmReap(driver, vm, 0);
-                libxlVmStart(driver, vm, 0);
+                libxlVmStart(driver, vm, 0, -1);
                 break;
             default:
                 VIR_INFO("Unhandled shutdown_reason %d", info.shutdown_reason);
@@ -504,8 +504,8 @@ cleanup:
  * virDomainObjPtr should be locked on invocation
  */
 static int
-libxlVmStart(libxlDriverPrivatePtr driver,
-             virDomainObjPtr vm, bool start_paused)
+libxlVmStart(libxlDriverPrivatePtr driver, virDomainObjPtr vm,
+             bool start_paused, int restore_fd)
 {
     libxl_domain_config d_config;
     virDomainDefPtr def = vm->def;
@@ -524,12 +524,23 @@ libxlVmStart(libxlDriverPrivatePtr driver,
     //TODO: Balloon dom0 ??
     //ret = freemem(&d_config->b_info, &d_config->dm_info);

-    ret = libxl_domain_create_new(&priv->ctx, &d_config,
-                                  NULL, &child_console_pid, &domid);
+    if (restore_fd < 0)
+        ret = libxl_domain_create_new(&priv->ctx, &d_config,
+                                      NULL, &child_console_pid, &domid);
+    else
+        ret = libxl_domain_create_restore(&priv->ctx, &d_config, NULL,
+                                          &child_console_pid, &domid,
+                                          restore_fd);
+
     if (ret) {
-        libxlError(VIR_ERR_INTERNAL_ERROR,
-                   _("libxenlight failed to create new domain '%s'"),
-                   d_config.c_info.name);
+        if (restore_fd < 0)
+            libxlError(VIR_ERR_INTERNAL_ERROR,
+                       _("libxenlight failed to create new domain '%s'"),
+                       d_config.c_info.name);
+        else
+            libxlError(VIR_ERR_INTERNAL_ERROR,
+                       _("libxenlight failed to restore domain '%s'"),
+                       d_config.c_info.name);
         goto error;
     }

@@ -562,7 +573,9 @@ libxlVmStart(libxlDriverPrivatePtr driver,
         goto error;

     event = virDomainEventNewFromObj(vm, VIR_DOMAIN_EVENT_STARTED,
-                                     VIR_DOMAIN_EVENT_STARTED_BOOTED);
+                                     restore_fd < 0 ?
+                                         VIR_DOMAIN_EVENT_STARTED_BOOTED :
+                                         VIR_DOMAIN_EVENT_STARTED_RESTORED);
     libxlDomainEventQueue(driver, event);

     libxl_domain_config_destroy(&d_config);
@@ -1046,7 +1059,8 @@ libxlDomainCreateXML(virConnectPtr conn, const char *xml,
         goto cleanup;
     def = NULL;

-    if (libxlVmStart(driver, vm, (flags & VIR_DOMAIN_START_PAUSED) != 0) < 0) {
+    if (libxlVmStart(driver, vm, (flags & VIR_DOMAIN_START_PAUSED) != 0,
+                     -1) < 0) {
         virDomainRemoveInactive(&driver->domains, vm);
         vm = NULL;
         goto cleanup;
@@ -1566,6 +1580,186 @@ libxlDomainGetInfo(virDomainPtr dom, virDomainInfoPtr info)
 }

 static int
+libxlDomainSave(virDomainPtr dom, const char * to)
+{
+    libxlDriverPrivatePtr driver = dom->conn->privateData;
+    virDomainObjPtr vm;
+    libxlDomainObjPrivatePtr priv;
+    virDomainEventPtr event = NULL;
+    libxlSavefileHeader hdr;
+    libxl_domain_suspend_info s_info;
+    char *xml;
+    uint32_t xml_len;
+    int fd;
+    int ret = -1;
+
+    libxlDriverLock(driver);
+    vm = virDomainFindByUUID(&driver->domains, dom->uuid);
+
+    if (!vm) {
+        char uuidstr[VIR_UUID_STRING_BUFLEN];
+        virUUIDFormat(dom->uuid, uuidstr);
+        libxlError(VIR_ERR_NO_DOMAIN,
+                   _("No domain with matching uuid '%s'"), uuidstr);
+        goto cleanup;
+    }
+
+    if (!virDomainObjIsActive(vm)) {
+        libxlError(VIR_ERR_OPERATION_INVALID, "%s", _("Domain is not running"));
+        goto cleanup;
+    }
+
+    priv = vm->privateData;
+
+    if (vm->state != VIR_DOMAIN_PAUSED) {
+        memset(&s_info, 0, sizeof(s_info));
+
+        if ((fd = virFileOpenAs(to, O_CREAT|O_TRUNC|O_WRONLY, S_IRUSR|S_IWUSR,
+                                getuid(), getgid(), 0)) < 0) {
+            virReportSystemError(-fd,
+                                 _("Failed to create domain save file '%s'"),
+                                 to);
+            goto cleanup;
+        }
+
+        if ((xml = virDomainDefFormat(vm->def, 0)) == NULL)
+            goto cleanup;
+        xml_len = strlen(xml) + 1;
+
+        memset(&hdr, 0, sizeof(hdr));
+        memcpy(hdr.magic, LIBXL_SAVE_MAGIC, sizeof(hdr.magic));
+        hdr.version = LIBXL_SAVE_VERSION;
+        hdr.xmlLen = xml_len;
+
+        if (safewrite(fd, &hdr, sizeof(hdr)) != sizeof(hdr)) {
+            libxlError(VIR_ERR_OPERATION_FAILED,
+                       _("Failed to write save file header"));
+            goto cleanup;
+        }
+
+        if (safewrite(fd, xml, xml_len) != xml_len) {
+            libxlError(VIR_ERR_OPERATION_FAILED,
+                       _("Failed to write xml description"));
+            goto cleanup;
+        }
+
+        if (libxl_domain_suspend(&priv->ctx, &s_info, dom->id, fd) != 0) {
+            libxlError(VIR_ERR_INTERNAL_ERROR,
+                       _("Failed to save domain '%d' with libxenlight"),
+                       dom->id);
+            goto cleanup;
+        }
+
+        event = virDomainEventNewFromObj(vm, VIR_DOMAIN_EVENT_STOPPED,
+                                         VIR_DOMAIN_EVENT_STOPPED_SAVED);
+
+        if (libxlVmReap(driver, vm, 1) != 0) {
+            libxlError(VIR_ERR_INTERNAL_ERROR,
+                       _("Failed to destroy domain '%d'"), dom->id);
+            goto cleanup;
+        }
+
+        if (!vm->persistent) {
+            virDomainRemoveInactive(&driver->domains, vm);
+            vm = NULL;
+        }
+        ret = 0;
+    }
+cleanup:
+    VIR_FREE(xml);
+    if (VIR_CLOSE(fd) < 0)
+        virReportSystemError(errno, "%s", _("cannot close file"));
+    if (vm)
+        virDomainObjUnlock(vm);
+    if (event)
+        libxlDomainEventQueue(driver, event);
+    libxlDriverUnlock(driver);
+    return ret;
+}
+
+static int
+libxlDomainRestore(virConnectPtr conn, const char * from)
+{
+    libxlDriverPrivatePtr driver = conn->privateData;
+    virDomainDefPtr def = NULL;
+    virDomainObjPtr vm = NULL;
+    libxlSavefileHeader hdr;
+    char *xml = NULL;
+    int fd;
+    int ret = -1;
+
+    libxlDriverLock(driver);
+
+    if ((fd = virFileOpenAs(from, O_RDONLY, 0, getuid(), getgid(), 0)) < 0) {
+        libxlError(VIR_ERR_OPERATION_FAILED,
+                   "%s", _("cannot read domain image"));
+        goto cleanup;
+    }
+
+    if (saferead(fd, &hdr, sizeof(hdr)) != sizeof(hdr)) {
+        libxlError(VIR_ERR_OPERATION_FAILED,
+                   "%s", _("failed to read libxl header"));
+        goto cleanup;
+    }
+
+    if (memcmp(hdr.magic, LIBXL_SAVE_MAGIC, sizeof(hdr.magic))) {
+        libxlError(VIR_ERR_INVALID_ARG, "%s", _("image magic is incorrect"));
+        goto cleanup;
+    }
+
+    if (hdr.version > LIBXL_SAVE_VERSION) {
+        libxlError(VIR_ERR_OPERATION_FAILED,
+                   _("image version is not supported (%d > %d)"),
+                   hdr.version, LIBXL_SAVE_VERSION);
+        goto cleanup;
+    }
+
+    if (hdr.xmlLen <= 0) {
+        libxlError(VIR_ERR_OPERATION_FAILED,
+                   _("invalid XML length: %d"), hdr.xmlLen);
+        goto cleanup;
+    }
+
+    if (VIR_ALLOC_N(xml, hdr.xmlLen) < 0) {
+        virReportOOMError();
+        goto cleanup;
+    }
+
+    if (saferead(fd, xml, hdr.xmlLen) != hdr.xmlLen) {
+        libxlError(VIR_ERR_OPERATION_FAILED, "%s", _("failed to read XML"));
+        goto cleanup;
+    }
+
+    if (!(def = virDomainDefParseString(driver->caps, xml,
+                                        VIR_DOMAIN_XML_INACTIVE)))
+        goto cleanup;
+
+    if (virDomainObjIsDuplicate(&driver->domains, def, 1) < 0)
+        goto cleanup;
+
+    if (!(vm = virDomainAssignDef(driver->caps, &driver->domains, def, true)))
+        goto cleanup;
+
+    def = NULL;
+
+    if ((ret = libxlVmStart(driver, vm, false, fd)) < 0 &&
+        !vm->persistent) {
+        virDomainRemoveInactive(&driver->domains, vm);
+        vm = NULL;
+    }
+
+cleanup:
+    VIR_FREE(xml);
+    virDomainDefFree(def);
+    if (VIR_CLOSE(fd) < 0)
+        virReportSystemError(errno, "%s", _("cannot close file"));
+    if (vm)
+        virDomainObjUnlock(vm);
+    libxlDriverUnlock(driver);
+    return ret;
+}
+
+static int
 libxlDomainSetVcpusFlags(virDomainPtr dom, unsigned int nvcpus,
                          unsigned int flags)
 {
@@ -2036,7 +2230,7 @@ libxlDomainCreateWithFlags(virDomainPtr dom,
         goto cleanup;
     }

-    ret = libxlVmStart(driver, vm, (flags & VIR_DOMAIN_START_PAUSED) != 0);
+    ret = libxlVmStart(driver, vm, (flags & VIR_DOMAIN_START_PAUSED) != 0, -1);

 cleanup:
     if (vm)
@@ -2672,8 +2866,8 @@ static virDriver libxlDriver = {
     NULL,                       /* domainSetBlkioParameters */
     NULL,                       /* domainGetBlkioParameters */
     libxlDomainGetInfo,         /* domainGetInfo */
-    NULL,                       /* domainSave */
-    NULL,                       /* domainRestore */
+    libxlDomainSave,            /* domainSave */
+    libxlDomainRestore,         /* domainRestore */
     NULL,                       /* domainCoreDump */
     libxlDomainSetVcpus,        /* domainSetVcpus */
     libxlDomainSetVcpusFlags,   /* domainSetVcpusFlags */
--
1.7.1


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