btrfs: add cancellation points to defrag

The defrag operation can take very long, we want to have a way how to
cancel it. The code checks for a pending signal at safe points in the
defrag loops and returns EAGAIN. This means a user can press ^C after
running 'btrfs fi defrag', woks for both defrag modes, files and root.

Returning from the command was instant in my light tests, but may take
longer depending on the aging factor of the filesystem.

Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 6d6314406e27..d02ec577f70f 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1202,6 +1202,12 @@ int btrfs_defrag_file(struct inode *inode, struct file *file,
                 if (!(inode->i_sb->s_flags & MS_ACTIVE))
                         break;
 
+                if (btrfs_defrag_cancelled(root->fs_info)) {
+                        printk(KERN_DEBUG "btrfs: defrag_file cancelled\n");
+                        ret = -EAGAIN;
+                        break;
+                }
+
                 if (!should_defrag_range(inode, (u64)i << PAGE_CACHE_SHIFT,
                                          extent_thresh, &last_len, &skip,
                                          &defrag_end, range->flags &