fs: add hole punching to fallocate

Hole punching has already been implemented by XFS and OCFS2, and has the
potential to be implemented on both BTRFS and EXT4 so we need a generic way to
get to this feature.  The simplest way in my mind is to add FALLOC_FL_PUNCH_HOLE
to fallocate() since it already looks like the normal fallocate() operation.
I've tested this patch with XFS and BTRFS to make sure XFS did what it's
supposed to do and that BTRFS failed like it was supposed to.  Thank you,

Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 6 insertions, 1 deletions

diff --git a/fs/open.c b/fs/open.c
index 4197b9ed023d..5b6ef7e2859e 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -223,7 +223,12 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
                 return -EINVAL;
 
         /* Return error if mode is not supported */
-        if (mode && !(mode & FALLOC_FL_KEEP_SIZE))
+        if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
+                return -EOPNOTSUPP;
+
+        /* Punch hole must have keep size set */
+        if ((mode & FALLOC_FL_PUNCH_HOLE) &&
+            !(mode & FALLOC_FL_KEEP_SIZE))
                 return -EOPNOTSUPP;
 
         if (!(file->f_mode & FMODE_WRITE))