[Qemu-devel] [PATCH 1/2] Add virtagent file system freeze/thaw

[Jes.Sorensen@redhat.com]

From: Jes Sorensen <Jes.Sorensen@redhat.com>

Implement freeze/thaw support in the guest, allowing the host to
request the guest freezes all it's file systems before a live snapshot
is performed.
 - fsfreeze(): Walk the list of mounted local real file systems,
               and freeze them.
 - fsthaw():   Walk the list of previously frozen file systems and
               thaw them.
 - fsstatus(): Return the current status of freeze/thaw. The host must
               poll this function, in case fsfreeze() returned with a
	       timeout, to wait for the operation to finish.

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
---
 virtagent-common.h |    8 ++
 virtagent-server.c |  195 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 203 insertions(+), 0 deletions(-)

diff --git a/virtagent-common.h b/virtagent-common.h
index 5d8f5c1..7c6d9ef 100644
--- a/virtagent-common.h
+++ b/virtagent-common.h
@@ -61,6 +61,14 @@ typedef struct VAContext {
     const char *channel_path;
 } VAContext;
 
+enum va_fsfreeze_status {
+    FREEZE_ERROR = -1,
+    FREEZE_THAWED = 0,
+    FREEZE_INPROGRESS = 1,
+    FREEZE_FROZEN = 2,
+    FREEZE_THAWINPROGRESS = 3,
+};
+
 enum va_job_status {
     VA_JOB_STATUS_PENDING = 0,
     VA_JOB_STATUS_OK,
diff --git a/virtagent-server.c b/virtagent-server.c
index 7bb35b2..5140918 100644
--- a/virtagent-server.c
+++ b/virtagent-server.c
@@ -14,6 +14,10 @@
 #include <syslog.h>
 #include "qemu_socket.h"
 #include "virtagent-common.h"
+#include <mntent.h>
+#include <sys/types.h>
+#include <sys/ioctl.h>
+#include <linux/fs.h>
 
 static VAServerData *va_server_data;
 static bool va_enable_syslog = false; /* enable syslog'ing of RPCs */
@@ -217,6 +221,191 @@ static xmlrpc_value *va_hello(xmlrpc_env *env,
     return result;
 }
 
+
+/*
+ * Walk the mount table and build a list of local file systems
+ */
+
+struct direntry {
+    char *dirname;
+    char *devtype;
+    struct direntry *next;
+};
+
+struct va_freezestate {
+    struct direntry *mount_list;
+    int status;
+};
+
+static struct va_freezestate freezestate;
+
+static int build_mount_list(void)
+{
+    struct mntent *mnt;
+    struct direntry *entry;
+    struct direntry *next;
+    char const *mtab = MOUNTED;
+    FILE *fp;
+
+    fp = setmntent(mtab, "r");
+    if (!fp) {
+        fprintf(stderr, "unable to read mtab\n");
+        goto fail;
+    }
+
+    while ((mnt = getmntent(fp))) {
+        /*
+         * An entry which device name doesn't start with a '/' is
+         * either a dummy file system or a network file system.
+         * Add special handling for smbfs and cifs as is done by
+         * coreutils as well.
+         */
+        if ((mnt->mnt_fsname[0] != '/') ||
+            (strcmp(mnt->mnt_type, "smbfs") == 0) ||
+            (strcmp(mnt->mnt_type, "cifs") == 0)) {
+            continue;
+        }
+
+        entry = qemu_malloc(sizeof(struct direntry));
+        entry->dirname = qemu_strdup(mnt->mnt_dir);
+        entry->devtype = qemu_strdup(mnt->mnt_type);
+        entry->next = freezestate.mount_list;
+
+        freezestate.mount_list = entry;
+    }
+
+    endmntent(fp);
+
+    return 0;
+ 
+fail:
+    while(freezestate.mount_list) {
+        next = freezestate.mount_list->next;
+        qemu_free(freezestate.mount_list->dirname);
+        qemu_free(freezestate.mount_list->devtype);
+        qemu_free(freezestate.mount_list);
+        freezestate.mount_list = next;
+    }
+
+    return -1;
+}
+
+/*
+ * va_fsfreeze(): Walk list of mounted file systems in the guest, and
+ *   freeze the ones which are real local file systems.
+ * rpc return values: Number of file systems frozen, -1 on error.
+ */
+static xmlrpc_value *va_fsfreeze(xmlrpc_env *env,
+                                 xmlrpc_value *params,
+                                 void *user_data)
+{
+    xmlrpc_int32 ret = 0, i = 0;
+    xmlrpc_value *result;
+    struct direntry *entry;
+    int fd;
+    SLOG("va_fsfreeze()");
+
+    if (freezestate.status != FREEZE_THAWED) {
+        ret = 0;
+        goto out;
+    }
+
+    ret = build_mount_list();
+    if (ret < 0) {
+        goto out;
+    }
+
+    freezestate.status = FREEZE_INPROGRESS;
+
+    entry = freezestate.mount_list;
+    while(entry) {
+        fd = qemu_open(entry->dirname, O_RDONLY);
+        if (fd == -1) {
+            ret = errno;
+            goto error;
+        }
+        ret = ioctl(fd, FIFREEZE);
+        close(fd);
+        if (ret < 0 && ret != EOPNOTSUPP) {
+            goto error;
+        }
+
+        entry = entry->next;
+        i++;
+    }
+
+    freezestate.status = FREEZE_FROZEN;
+    ret = i;
+out:
+    result = xmlrpc_build_value(env, "i", ret);
+    return result;
+error:
+    if (i > 0) {
+        freezestate.status = FREEZE_ERROR;
+    }
+    goto out;
+}
+
+/*
+ * va_fsthaw(): Walk list of frozen file systems in the guest, and
+ *   thaw them.
+ * rpc return values: Number of file systems thawed on success, -1 on error.
+ */
+static xmlrpc_value *va_fsthaw(xmlrpc_env *env,
+                               xmlrpc_value *params,
+                               void *user_data)
+{
+    xmlrpc_int32 ret;
+    xmlrpc_value *result;
+    struct direntry *entry;
+    int fd, i = 0;
+    SLOG("va_fsthaw()");
+
+    if (freezestate.status != FREEZE_FROZEN) {
+        ret = 0;
+        goto out;
+    }
+
+    while((entry = freezestate.mount_list)) {
+        fd = qemu_open(entry->dirname, O_RDONLY);
+        if (fd == -1) {
+            ret = -1;
+            goto out;
+        }
+        ret = ioctl(fd, FITHAW);
+        close(fd);
+        if (ret < 0 && ret != EOPNOTSUPP) {
+            ret = -1;
+            goto out;
+        }
+
+        freezestate.mount_list = entry->next;
+        qemu_free(entry->dirname);
+        qemu_free(entry->devtype);
+        qemu_free(entry);
+        i++;
+    }
+
+    freezestate.status = FREEZE_THAWED;
+    ret = i;
+out:
+    result = xmlrpc_build_value(env, "i", ret);
+    return result;
+}
+
+/*
+ * va_fsstatus(): Return status of freeze/thaw
+ * rpc return values: fsfreeze_status
+ */
+static xmlrpc_value *va_fsstatus(xmlrpc_env *env,
+                                 xmlrpc_value *params,
+                                 void *user_data)
+{
+    xmlrpc_value *result = xmlrpc_build_value(env, "i", freezestate.status);
+    SLOG("va_fsstatus()");
+    return result;
+}
+
 typedef struct RPCFunction {
     xmlrpc_value *(*func)(xmlrpc_env *env, xmlrpc_value *param, void *unused);
     const char *func_name;
@@ -237,6 +426,12 @@ static RPCFunction guest_functions[] = {
       .func_name = "va.ping" },
     { .func = va_capabilities,
       .func_name = "va.capabilities" },
+    { .func = va_fsfreeze,
+      .func_name = "va.fsfreeze" },
+    { .func = va_fsthaw,
+      .func_name = "va.fsthaw" },
+    { .func = va_fsstatus,
+      .func_name = "va.fsstatus" },
     { NULL, NULL }
 };
 static RPCFunction host_functions[] = {
-- 
1.7.3.5