qga: Move Linux-specific FS freeze/thaw code to a separate file

In the next patches we are going to add FreeBSD support for QEMU Guest
Agent. In the result, code in commands-posix.c will be too cumbersome.

Move Linux-specific FS freeze/thaw code to a separate file commands-linux.c
keeping common POSIX code in commands-posix.c.

Reviewed-by: Konstantin Kostiuk <kkostiuk@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
Signed-off-by: Konstantin Kostiuk <kkostiuk@redhat.com>

qga/commands-common.h

@@ -10,6 +10,40 @@
 #define QGA_COMMANDS_COMMON_H
 
 #include "qga-qapi-types.h"
+#include "guest-agent-core.h"
+#include "qemu/queue.h"
+
+#if defined(__linux__)
+#include <linux/fs.h>
+#ifdef FIFREEZE
+#define CONFIG_FSFREEZE
+#endif
+#ifdef FITRIM
+#define CONFIG_FSTRIM
+#endif
+#endif /* __linux__ */
+
+#if defined(CONFIG_FSFREEZE) || defined(CONFIG_FSTRIM)
+typedef struct FsMount {
+    char *dirname;
+    char *devtype;
+    unsigned int devmajor, devminor;
+    QTAILQ_ENTRY(FsMount) next;
+} FsMount;
+
+typedef QTAILQ_HEAD(FsMountList, FsMount) FsMountList;
+
+bool build_fs_mount_list(FsMountList *mounts, Error **errp);
+void free_fs_mount_list(FsMountList *mounts);
+#endif /* CONFIG_FSFREEZE || CONFIG_FSTRIM */
+
+#if defined(CONFIG_FSFREEZE)
+int64_t qmp_guest_fsfreeze_do_freeze_list(bool has_mountpoints,
+                                          strList *mountpoints,
+                                          FsMountList mounts,
+                                          Error **errp);
+int qmp_guest_fsfreeze_do_thaw(Error **errp);
+#endif /* CONFIG_FSFREEZE */
 
 typedef struct GuestFileHandle GuestFileHandle;
 

qga/commands-linux.c

@@ -0,0 +1,286 @@
+/*
+ * QEMU Guest Agent Linux-specific command implementations
+ *
+ * Copyright IBM Corp. 2011
+ *
+ * Authors:
+ *  Michael Roth      <mdroth@linux.vnet.ibm.com>
+ *  Michal Privoznik  <mprivozn@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "commands-common.h"
+#include "cutils.h"
+#include <mntent.h>
+#include <sys/ioctl.h>
+
+#if defined(CONFIG_FSFREEZE) || defined(CONFIG_FSTRIM)
+static int dev_major_minor(const char *devpath,
+                           unsigned int *devmajor, unsigned int *devminor)
+{
+    struct stat st;
+
+    *devmajor = 0;
+    *devminor = 0;
+
+    if (stat(devpath, &st) < 0) {
+        slog("failed to stat device file '%s': %s", devpath, strerror(errno));
+        return -1;
+    }
+    if (S_ISDIR(st.st_mode)) {
+        /* It is bind mount */
+        return -2;
+    }
+    if (S_ISBLK(st.st_mode)) {
+        *devmajor = major(st.st_rdev);
+        *devminor = minor(st.st_rdev);
+        return 0;
+    }
+    return -1;
+}
+
+static bool build_fs_mount_list_from_mtab(FsMountList *mounts, Error **errp)
+{
+    struct mntent *ment;
+    FsMount *mount;
+    char const *mtab = "/proc/self/mounts";
+    FILE *fp;
+    unsigned int devmajor, devminor;
+
+    fp = setmntent(mtab, "r");
+    if (!fp) {
+        error_setg(errp, "failed to open mtab file: '%s'", mtab);
+        return false;
+    }
+
+    while ((ment = 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 ((ment->mnt_fsname[0] != '/') ||
+            (strcmp(ment->mnt_type, "smbfs") == 0) ||
+            (strcmp(ment->mnt_type, "cifs") == 0)) {
+            continue;
+        }
+        if (dev_major_minor(ment->mnt_fsname, &devmajor, &devminor) == -2) {
+            /* Skip bind mounts */
+            continue;
+        }
+
+        mount = g_new0(FsMount, 1);
+        mount->dirname = g_strdup(ment->mnt_dir);
+        mount->devtype = g_strdup(ment->mnt_type);
+        mount->devmajor = devmajor;
+        mount->devminor = devminor;
+
+        QTAILQ_INSERT_TAIL(mounts, mount, next);
+    }
+
+    endmntent(fp);
+    return true;
+}
+
+static void decode_mntname(char *name, int len)
+{
+    int i, j = 0;
+    for (i = 0; i <= len; i++) {
+        if (name[i] != '\\') {
+            name[j++] = name[i];
+        } else if (name[i + 1] == '\\') {
+            name[j++] = '\\';
+            i++;
+        } else if (name[i + 1] >= '0' && name[i + 1] <= '3' &&
+                   name[i + 2] >= '0' && name[i + 2] <= '7' &&
+                   name[i + 3] >= '0' && name[i + 3] <= '7') {
+            name[j++] = (name[i + 1] - '0') * 64 +
+                        (name[i + 2] - '0') * 8 +
+                        (name[i + 3] - '0');
+            i += 3;
+        } else {
+            name[j++] = name[i];
+        }
+    }
+}
+
+/*
+ * Walk the mount table and build a list of local file systems
+ */
+bool build_fs_mount_list(FsMountList *mounts, Error **errp)
+{
+    FsMount *mount;
+    char const *mountinfo = "/proc/self/mountinfo";
+    FILE *fp;
+    char *line = NULL, *dash;
+    size_t n;
+    char check;
+    unsigned int devmajor, devminor;
+    int ret, dir_s, dir_e, type_s, type_e, dev_s, dev_e;
+
+    fp = fopen(mountinfo, "r");
+    if (!fp) {
+        return build_fs_mount_list_from_mtab(mounts, errp);
+    }
+
+    while (getline(&line, &n, fp) != -1) {
+        ret = sscanf(line, "%*u %*u %u:%u %*s %n%*s%n%c",
+                     &devmajor, &devminor, &dir_s, &dir_e, &check);
+        if (ret < 3) {
+            continue;
+        }
+        dash = strstr(line + dir_e, " - ");
+        if (!dash) {
+            continue;
+        }
+        ret = sscanf(dash, " - %n%*s%n %n%*s%n%c",
+                     &type_s, &type_e, &dev_s, &dev_e, &check);
+        if (ret < 1) {
+            continue;
+        }
+        line[dir_e] = 0;
+        dash[type_e] = 0;
+        dash[dev_e] = 0;
+        decode_mntname(line + dir_s, dir_e - dir_s);
+        decode_mntname(dash + dev_s, dev_e - dev_s);
+        if (devmajor == 0) {
+            /* btrfs reports major number = 0 */
+            if (strcmp("btrfs", dash + type_s) != 0 ||
+                dev_major_minor(dash + dev_s, &devmajor, &devminor) < 0) {
+                continue;
+            }
+        }
+
+        mount = g_new0(FsMount, 1);
+        mount->dirname = g_strdup(line + dir_s);
+        mount->devtype = g_strdup(dash + type_s);
+        mount->devmajor = devmajor;
+        mount->devminor = devminor;
+
+        QTAILQ_INSERT_TAIL(mounts, mount, next);
+    }
+    free(line);
+
+    fclose(fp);
+    return true;
+}
+#endif /* CONFIG_FSFREEZE || CONFIG_FSTRIM */
+
+#ifdef CONFIG_FSFREEZE
+/*
+ * Walk list of mounted file systems in the guest, and freeze the ones which
+ * are real local file systems.
+ */
+int64_t qmp_guest_fsfreeze_do_freeze_list(bool has_mountpoints,
+                                          strList *mountpoints,
+                                          FsMountList mounts,
+                                          Error **errp)
+{
+    struct FsMount *mount;
+    strList *list;
+    int fd, ret, i = 0;
+
+    QTAILQ_FOREACH_REVERSE(mount, &mounts, next) {
+        /* To issue fsfreeze in the reverse order of mounts, check if the
+         * mount is listed in the list here */
+        if (has_mountpoints) {
+            for (list = mountpoints; list; list = list->next) {
+                if (strcmp(list->value, mount->dirname) == 0) {
+                    break;
+                }
+            }
+            if (!list) {
+                continue;
+            }
+        }
+
+        fd = qga_open_cloexec(mount->dirname, O_RDONLY, 0);
+        if (fd == -1) {
+            error_setg_errno(errp, errno, "failed to open %s", mount->dirname);
+            return -1;
+        }
+
+        /* we try to cull filesystems we know won't work in advance, but other
+         * filesystems may not implement fsfreeze for less obvious reasons.
+         * these will report EOPNOTSUPP. we simply ignore these when tallying
+         * the number of frozen filesystems.
+         * if a filesystem is mounted more than once (aka bind mount) a
+         * consecutive attempt to freeze an already frozen filesystem will
+         * return EBUSY.
+         *
+         * any other error means a failure to freeze a filesystem we
+         * expect to be freezable, so return an error in those cases
+         * and return system to thawed state.
+         */
+        ret = ioctl(fd, FIFREEZE);
+        if (ret == -1) {
+            if (errno != EOPNOTSUPP && errno != EBUSY) {
+                error_setg_errno(errp, errno, "failed to freeze %s",
+                                 mount->dirname);
+                close(fd);
+                return -1;
+            }
+        } else {
+            i++;
+        }
+        close(fd);
+    }
+    return i;
+}
+
+int qmp_guest_fsfreeze_do_thaw(Error **errp)
+{
+    int ret;
+    FsMountList mounts;
+    FsMount *mount;
+    int fd, i = 0, logged;
+    Error *local_err = NULL;
+
+    QTAILQ_INIT(&mounts);
+    if (!build_fs_mount_list(&mounts, &local_err)) {
+        error_propagate(errp, local_err);
+        return -1;
+    }
+
+    QTAILQ_FOREACH(mount, &mounts, next) {
+        logged = false;
+        fd = qga_open_cloexec(mount->dirname, O_RDONLY, 0);
+        if (fd == -1) {
+            continue;
+        }
+        /* we have no way of knowing whether a filesystem was actually unfrozen
+         * as a result of a successful call to FITHAW, only that if an error
+         * was returned the filesystem was *not* unfrozen by that particular
+         * call.
+         *
+         * since multiple preceding FIFREEZEs require multiple calls to FITHAW
+         * to unfreeze, continuing issuing FITHAW until an error is returned,
+         * in which case either the filesystem is in an unfreezable state, or,
+         * more likely, it was thawed previously (and remains so afterward).
+         *
+         * also, since the most recent successful call is the one that did
+         * the actual unfreeze, we can use this to provide an accurate count
+         * of the number of filesystems unfrozen by guest-fsfreeze-thaw, which
+         * may * be useful for determining whether a filesystem was unfrozen
+         * during the freeze/thaw phase by a process other than qemu-ga.
+         */
+        do {
+            ret = ioctl(fd, FITHAW);
+            if (ret == 0 && !logged) {
+                i++;
+                logged = true;
+            }
+        } while (ret == 0);
+        close(fd);
+    }
+
+    free_fs_mount_list(&mounts);
+
+    return i;
+}
+#endif /* CONFIG_FSFREEZE */