vfs: add a FALLOC_FL_UNSHARE mode to fallocate to unshare a range of blocks

Add a new fallocate mode flag that explicitly unshares blocks on
filesystems that support such features.  The new flag can only
be used with an allocate-mode fallocate call.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/fs/open.c b/fs/open.c
index 4fd6e25..d58525d 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -256,6 +256,11 @@ int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 	    (mode & ~FALLOC_FL_INSERT_RANGE))
 		return -EINVAL;
 
+	/* Unshare range should only be used with allocate mode. */
+	if ((mode & FALLOC_FL_UNSHARE_RANGE) &&
+	    (mode & ~(FALLOC_FL_UNSHARE_RANGE | FALLOC_FL_KEEP_SIZE)))
+		return -EINVAL;
+
 	if (!(file->f_mode & FMODE_WRITE))
 		return -EBADF;