btrfs: export global block reserve size as space_info

Introduce a block group type bit for a global reserve and fill the space
info for SPACE_INFO ioctl. This should replace the newly added ioctl
(01e219e8069516cdb98594d417b8bb8d906ed30d) to get just the 'size' part
of the global reserve, while the actual usage can be now visible in the
'btrfs fi df' output during ENOSPC stress.

The unpatched userspace tools will show the blockgroup as 'unknown'.

CC: Jeff Mahoney <jeffm@suse.com>
CC: Josef Bacik <jbacik@fb.com>
Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>

2 files changed, 28 insertions, 1 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index d8a669ed5506..ad1a5943a923 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -987,7 +987,8 @@ struct btrfs_dev_replace_item {
 #define BTRFS_BLOCK_GROUP_RAID10        (1ULL << 6)
 #define BTRFS_BLOCK_GROUP_RAID5         (1ULL << 7)
 #define BTRFS_BLOCK_GROUP_RAID6         (1ULL << 8)
-#define BTRFS_BLOCK_GROUP_RESERVED      BTRFS_AVAIL_ALLOC_BIT_SINGLE
+#define BTRFS_BLOCK_GROUP_RESERVED      (BTRFS_AVAIL_ALLOC_BIT_SINGLE | \
+                                         BTRFS_SPACE_INFO_GLOBAL_RSV)
 
 enum btrfs_raid_types {
         BTRFS_RAID_RAID10,
@@ -1019,6 +1020,12 @@ enum btrfs_raid_types {
  */
 #define BTRFS_AVAIL_ALLOC_BIT_SINGLE    (1ULL << 48)
 
+/*
+ * A fake block group type that is used to communicate global block reserve
+ * size to userspace via the SPACE_INFO ioctl.
+ */
+#define BTRFS_SPACE_INFO_GLOBAL_RSV     (1ULL << 49)
+
 #define BTRFS_EXTENDED_PROFILE_MASK     (BTRFS_BLOCK_GROUP_PROFILE_MASK | \
                                          BTRFS_AVAIL_ALLOC_BIT_SINGLE)
 
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 89d5db7eb452..f2e8fcc279a3 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3562,6 +3562,11 @@ static long btrfs_ioctl_space_info(struct btrfs_root *root, void __user *arg)
                 up_read(&info->groups_sem);
         }
 
+        /*
+         * Global block reserve, exported as a space_info
+         */
+        slot_count++;
+
         /* space_slots == 0 means they are asking for a count */
         if (space_args.space_slots == 0) {
                 space_args.total_spaces = slot_count;
@@ -3620,6 +3625,21 @@ static long btrfs_ioctl_space_info(struct btrfs_root *root, void __user *arg)
                 up_read(&info->groups_sem);
         }
 
+        /*
+         * Add global block reserve
+         */
+        if (slot_count) {
+                struct btrfs_block_rsv *block_rsv = &root->fs_info->global_block_rsv;
+
+                spin_lock(&block_rsv->lock);
+                space.total_bytes = block_rsv->size;
+                space.used_bytes = block_rsv->size - block_rsv->reserved;
+                spin_unlock(&block_rsv->lock);
+                space.flags = BTRFS_SPACE_INFO_GLOBAL_RSV;
+                memcpy(dest, &space, sizeof(space));
+                space_args.total_spaces++;
+        }
+
         user_dest = (struct btrfs_ioctl_space_info __user *)
                 (arg + sizeof(struct btrfs_ioctl_space_args));