btrfs: add ioctl to export size of global metadata reservation

btrfs filesystem df output will show the size of the metadata space
and how much of it is used, and the user assumes that the difference
is all usable space. Since that's not actually the case due to the
global metadata reservation, we should provide the full picture to the
user.

This patch adds an ioctl that exports the size of the global metadata
reservation so that btrfs filesystem df can report it.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 93b01fe6c73107e84e7283205b95d2faa6a4128d..60d3d37ef9a2320166b98ed6018f468322a22616 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3498,6 +3498,20 @@ out:
        return ret;
 }
 
+static long btrfs_ioctl_global_rsv(struct btrfs_root *root, void __user *arg)
+{
+       struct btrfs_block_rsv *block_rsv = &root->fs_info->global_block_rsv;
+       u64 reserved;
+
+       spin_lock(&block_rsv->lock);
+       reserved = block_rsv->reserved;
+       spin_unlock(&block_rsv->lock);
+
+       if (arg && copy_to_user(arg, &reserved, sizeof(reserved)))
+               return -EFAULT;
+       return 0;
+}
+
 /*
  * there are many ways the trans_start and trans_end ioctls can lead
  * to deadlocks.  They should only be used by applications that
@@ -4706,6 +4720,8 @@ long btrfs_ioctl(struct file *file, unsigned int
                return btrfs_ioctl_logical_to_ino(root, argp);
        case BTRFS_IOC_SPACE_INFO:
                return btrfs_ioctl_space_info(root, argp);
+       case BTRFS_IOC_GLOBAL_RSV:
+               return btrfs_ioctl_global_rsv(root, argp);
        case BTRFS_IOC_SYNC: {
                int ret;
 

diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index b4d69092fbdbea488f4998c8e9fd4e158cf2465f..1b8a0f4c95900b14e7d6f71fa54523409d3b2be6 100644 (file)
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -558,6 +558,7 @@ static inline char *btrfs_err_str(enum btrfs_err_code err_code)
 #define BTRFS_IOC_DEFAULT_SUBVOL _IOW(BTRFS_IOCTL_MAGIC, 19, __u64)
 #define BTRFS_IOC_SPACE_INFO _IOWR(BTRFS_IOCTL_MAGIC, 20, \
                                    struct btrfs_ioctl_space_args)
+#define BTRFS_IOC_GLOBAL_RSV _IOR(BTRFS_IOCTL_MAGIC, 20, __u64)
 #define BTRFS_IOC_START_SYNC _IOR(BTRFS_IOCTL_MAGIC, 24, __u64)
 #define BTRFS_IOC_WAIT_SYNC  _IOW(BTRFS_IOCTL_MAGIC, 22, __u64)
 #define BTRFS_IOC_SNAP_CREATE_V2 _IOW(BTRFS_IOCTL_MAGIC, 23, \