fallocate.2: Clarify the zeroing behavior

fallocate() zeroes only space that did not previously contain
data, but leaves existing data untouched.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

diff --git a/man2/fallocate.2 b/man2/fallocate.2
index f5c395dc12fc25ebfc1766ae963f3e0f10bdc0d7..f577ba849284d8a07675a4761bc09991b2872c29 100644 (file)
--- a/man2/fallocate.2
+++ b/man2/fallocate.2
@@ -44,8 +44,7 @@ The default operation (i.e.,
 .I mode
 is zero) of
 .BR fallocate ()
-allocates and initializes to zero the disk space
-within the range specified by
+allocates the disk space within the range specified by
 .I offset
 and
 .IR len .
@@ -54,6 +53,11 @@ The file size (as reported by
 will be changed if
 .IR offset + len
 is greater than the file size.
+Any subregion withing the range specified by
+.I offset
+and
+.IR len .
+that did not contain data before the call will be initialized to zero.
 This default behavior closely resembles the behavior of the
 .BR posix_fallocate (3)
 library function,