[PATCH 55/58] vfs: add a FALLOC_FL_UNSHARE mode to fallocate to unshare a range of blocks

Darrick J. Wong
2015-10-07T05:01:18Z

Add a new mode to fallocate that unshares a range of blocks.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
fs/open.c | 5 +++++
include/linux/falloc.h | 3 ++-
include/uapi/linux/falloc.h | 14 ++++++++++++++
3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/fs/open.c b/fs/open.c
index b6f1e96..58e2b61 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 exclusively. */
+ if ((mode & FALLOC_FL_UNSHARE_RANGE) &&
+ (mode & ~FALLOC_FL_UNSHARE_RANGE))
+ return -EINVAL;
+
if (!(file->f_mode & FMODE_WRITE))
return -EBADF;

diff --git a/include/linux/falloc.h b/include/linux/falloc.h
index 9961110..7494dc6 100644
--- a/include/linux/falloc.h
+++ b/include/linux/falloc.h
@@ -25,6 +25,7 @@ struct space_resv {
FALLOC_FL_PUNCH_HOLE | \
FALLOC_FL_COLLAPSE_RANGE | \
FALLOC_FL_ZERO_RANGE | \
- FALLOC_FL_INSERT_RANGE)
+ FALLOC_FL_INSERT_RANGE | \
+ FALLOC_FL_UNSHARE_RANGE)

#endif /* _FALLOC_H_ */
diff --git a/include/uapi/linux/falloc.h b/include/uapi/linux/falloc.h
index 3e445a7..a1c293b 100644
--- a/include/uapi/linux/falloc.h
+++ b/include/uapi/linux/falloc.h
@@ -58,4 +58,18 @@
*/
#define FALLOC_FL_INSERT_RANGE 0x20

+/*
+ * FALLOC_FL_UNSHARE_RANGE is used to unshare shared blocks within the
+ * file size without overwriting any existing data. The purpose of this
+ * call is to preemptively reallocate any blocks that are subject to
+ * copy-on-write.
+ *
+ * Different filesystems may implement different limitations on the
+ * granularity of the operation. Most will limit operations to filesystem
+ * block size boundaries, but this boundary may be larger or smaller
+ * depending on the filesystem and/or the configuration of the filesystem
+ * or file.
+ */
+#define FALLOC_FL_UNSHARE_RANGE 0x40
+
#endif /* _UAPI_FALLOC_H_ */