This functionality landed in Linux 2.6.38 since:
commit 79124f18b335172e1916075c633745e12dae1dac
Author: Josef Bacik <josef@xxxxxxxxxx>
Date: Wed Nov 17 20:46:15 2010 -0500
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,
CC: Josef Bacik <josef@xxxxxxxxxx>
CC: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Lucian Adrian Grijincu <lucian.grijincu@xxxxxxxxx>
---
man2/fallocate.2 | 22 +++++++++++++++++++++-
1 files changed, 21 insertions(+), 1 deletions(-)
diff --git a/man2/fallocate.2 b/man2/fallocate.2
index 42eefbd..1279130 100644
--- a/man2/fallocate.2
+++ b/man2/fallocate.2
@@ -32,7 +32,7 @@ bytes.
The
.I mode
argument determines the operation to be performed on the given range.
-Currently only one flag is supported for
+There are two flag values supported for
.IR mode :
.TP
.B FALLOC_FL_KEEP_SIZE
@@ -59,6 +59,26 @@ even if it is less than
.\" All of the above flags were debated upon and we can not say
.\" if any/which one of these flags will make it to the later kernels.
.PP
+.TP
+.BR FALLOC_FL_PUNCH_HOLE " (since Linux 2.6.38)
+Deallocate space inside a file in the byte range starting at
+.I offset
+and continuing for
+.I len
+bytes.
+Partial filesystem blocks are zeroed, and
+whole filesystem blocks are removed from the file.
+Currently you can only have
+.BR FALLOC_FL_PUNCH_HOLE
+with
+.BR FALLOC_FL_KEEP_SIZE
+set,
+so the file size (as reported by
+.BR stat (2))
+does not change
+when hole punching, even when puching the end of
+a file off.
+.PP
If
.B FALLOC_FL_KEEP_SIZE
flag is not specified in
