+/*
+ * Do the filesystem syncing work. For simple filesystems
+ * writeback_inodes_sb(sb) just dirties buffers with inodes so we have to
+ * submit IO for these buffers via __sync_blockdev(). This also speeds up the
+ * wait == 1 case since in that case write_inode() functions do
+ * sync_dirty_buffer() and thus effectively write one block at a time.
+ */
+static int __sync_filesystem(struct super_block *sb, int wait)
+{
+ /*
+ * This should be safe, as we require bdi backing to actually
+ * write out data in the first place
+ */
+ if (!sb->s_bdi || sb->s_bdi == &noop_backing_dev_info)
+ return 0;
+
+ if (sb->s_qcop && sb->s_qcop->quota_sync)
+ sb->s_qcop->quota_sync(sb, -1, wait);
+
+ if (wait)
+ sync_inodes_sb(sb);
+ else
+ writeback_inodes_sb(sb);
+
+ if (sb->s_op->sync_fs)
+ sb->s_op->sync_fs(sb, wait);
+ return __sync_blockdev(sb->s_bdev, wait);
+}
+
+/*
+ * Write out and wait upon all dirty data associated with this
+ * superblock. Filesystem data as well as the underlying block
+ * device. Takes the superblock lock.
+ */
+int sync_filesystem(struct super_block *sb)
+{
+ int ret;
+
+ /*
+ * We need to be protected against the filesystem going from
+ * r/o to r/w or vice versa.
+ */
+ WARN_ON(!rwsem_is_locked(&sb->s_umount));
+
+ /*
+ * No point in syncing out anything if the filesystem is read-only.
+ */
+ if (sb->s_flags & MS_RDONLY)
+ return 0;
+
+ ret = __sync_filesystem(sb, 0);
+ if (ret < 0)
+ return ret;
+ return __sync_filesystem(sb, 1);
+}
+EXPORT_SYMBOL_GPL(sync_filesystem);
+
+/*
+ * Sync all the data for all the filesystems (called by sys_sync() and
+ * emergency sync)
+ *
+ * This operation is careful to avoid the livelock which could easily happen
+ * if two or more filesystems are being continuously dirtied. s_need_sync
+ * is used only here. We set it against all filesystems and then clear it as
+ * we sync them. So redirtied filesystems are skipped.
+ *
+ * But if process A is currently running sync_filesystems and then process B
+ * calls sync_filesystems as well, process B will set all the s_need_sync
+ * flags again, which will cause process A to resync everything. Fix that with
+ * a local mutex.
+ */
+static void sync_filesystems(int wait)
+{
+ struct super_block *sb;
+ static DEFINE_MUTEX(mutex);
+
+ mutex_lock(&mutex); /* Could be down_interruptible */
+ spin_lock(&sb_lock);
+ list_for_each_entry(sb, &super_blocks, s_list)
+ sb->s_need_sync = 1;
+
+restart:
+ list_for_each_entry(sb, &super_blocks, s_list) {
+ if (!sb->s_need_sync)
+ continue;
+ sb->s_need_sync = 0;
+ sb->s_count++;
+ spin_unlock(&sb_lock);
+
+ down_read(&sb->s_umount);
+ if (!(sb->s_flags & MS_RDONLY) && sb->s_root && sb->s_bdi)
+ __sync_filesystem(sb, wait);
+ up_read(&sb->s_umount);
+
+ /* restart only when sb is no longer on the list */
+ spin_lock(&sb_lock);
+ if (__put_super_and_need_restart(sb))
+ goto restart;
+ }
+ spin_unlock(&sb_lock);
+ mutex_unlock(&mutex);
+}
+
+/*
+ * sync everything. Start out by waking pdflush, because that writes back
+ * all queues in parallel.
+ */