[PATCH 2/2 v3] btrfs: obtain used_bytes in BTRFS_IOC_FS_INFO ioctl

[Anand Jain <anand.jain@oracle.com>]

btrfs-progs has to read fs info from the kernel to
read the latest info instead of reading it from the disks,
which generally is a stale info after certain critical
operation.

getting used_bytes parameter will help to fix
	btrfs filesystem show --kernel
to show the current info of the fs

v2->v3:
	everything is changed dropped the plan to introduce
	the new ioctl, as of now filesystem show could 
	manage if we add the used_bytes parameter to the
	BTRFS_IOC_FS_INFO and
	Update the title from
	 add framework to read fs info and dev info from the kernel

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 fs/btrfs/ioctl.c           | 16 ++++++++++++++--
 include/uapi/linux/btrfs.h |  3 ++-
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 0e7bcc5..082c9fc 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2384,7 +2384,10 @@ static long btrfs_ioctl_fs_info(struct btrfs_root *root, void __user *arg)
 	struct btrfs_ioctl_fs_info_args *fi_args;
 	struct btrfs_device *device;
 	struct btrfs_device *next;
-	struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
+	struct btrfs_fs_info *info = root->fs_info;
+	struct btrfs_fs_devices *fs_devices = info->fs_devices;
+	struct btrfs_space_info *si;
+	u64 used_bytes = 0;
 	int ret = 0;
 
 	if (!capable(CAP_SYS_ADMIN))
@@ -2394,8 +2397,17 @@ static long btrfs_ioctl_fs_info(struct btrfs_root *root, void __user *arg)
 	if (!fi_args)
 		return -ENOMEM;
 
+	rcu_read_lock();
+	list_for_each_entry_rcu(si, &info->space_info, list) {
+		used_bytes += si->bytes_used + si->bytes_reserved
+				+ si->bytes_pinned + si->bytes_readonly
+				+ si->bytes_may_use;
+	}
+	rcu_read_unlock();
+	fi_args->used_bytes = used_bytes;
+
 	fi_args->num_devices = fs_devices->num_devices;
-	memcpy(&fi_args->fsid, root->fs_info->fsid, sizeof(fi_args->fsid));
+	memcpy(&fi_args->fsid, info->fsid, sizeof(fi_args->fsid));
 
 	mutex_lock(&fs_devices->device_list_mutex);
 	list_for_each_entry_safe(device, next, &fs_devices->devices, dev_list) {
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index de3ec34..44bac0c 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -181,7 +181,8 @@ struct btrfs_ioctl_fs_info_args {
 	__u64 max_id;				/* out */
 	__u64 num_devices;			/* out */
 	__u8 fsid[BTRFS_FSID_SIZE];		/* out */
-	__u64 reserved[124];			/* pad to 1k */
+	__u64 used_bytes;                       /* out */
+	__u64 reserved[123];			/* pad to 1k */
 };
 
 /* balance control ioctl modes */
-- 
1.8.1.227.g44fe835