diff mbox

[02/63] vfs: add a FALLOC_FL_UNSHARE mode to fallocate to unshare a range of blocks

Message ID 147520474825.29434.11791614565389664342.stgit@birch.djwong.org (mailing list archive)
State New, archived
Headers show

Commit Message

Darrick J. Wong Sept. 30, 2016, 3:05 a.m. UTC 
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>
---
 fs/open.c                   |    5 +++++
 include/linux/falloc.h      |    3 ++-
 include/uapi/linux/falloc.h |   18 ++++++++++++++++++
 3 files changed, 25 insertions(+), 1 deletion(-)



--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Comments

Christoph Hellwig Sept. 30, 2016, 7:08 a.m. UTC | #1 
On Thu, Sep 29, 2016 at 08:05:48PM -0700, Darrick J. Wong wrote:
> 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.

We will also need a manpage addition for this.  And while we're at
it an explanation of fallocate on COW files for btrfs, ocfs2 and
XFS as I don't think we are very coherent or obvious at the moment.

Well, maybe that's just future work.  For now:

Reviewed-by: Christoph Hellwig <hch@lst.de>
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
diff mbox

Patch

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;
 
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..b075f60 100644
--- a/include/uapi/linux/falloc.h
+++ b/include/uapi/linux/falloc.h
@@ -58,4 +58,22 @@ 
  */
 #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.
+ *
+ * This flag can only be used with allocate-mode fallocate, which is
+ * to say that it cannot be used with the punch, zero, collapse, or
+ * insert range modes.
+ */
+#define FALLOC_FL_UNSHARE_RANGE		0x40
+
 #endif /* _UAPI_FALLOC_H_ */