FALLOC_FL_ZERO_RANGE was added in Linux 3.14, for zeroing ranges in the allocated space in a file. Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx> --- v2: Rebase and update the description v3: Ext4 zero range on extent based files man2/fallocate.2 | 46 +++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 45 insertions(+), 1 deletion(-) diff --git a/man2/fallocate.2 b/man2/fallocate.2 index 73c4f12..0ffce71 100644 --- a/man2/fallocate.2 +++ b/man2/fallocate.2 @@ -180,6 +180,48 @@ ext4 (only for extent-based files) .\" commit 9eb79482a97152930b113b51dff530aba9e28c8e and XFS. .\" commit e1d8fb88a64c1f8094b9f6c3b6d2d9e6719c970d +.SS Zeroing file space +Specifying +.BR FALLOC_FL_ZERO_RANGE +flag (available since Linux 3.14) in +.I mode +zeroes space in the byte range starting at +.I offset +and continuing for +.I len +bytes. +Within the specified range, blocks are preallocated for the regions +that span the holes in the file. After a successful call, subsequent +reads from this range will return zeroes. + +Zeroing is done within the file system preferably by converting range into +unwritten extents which requires very little IO to be issued mostly for +metadata. This means that the range will not be physically zeroed out +on the device. + +If the +.B FALLOC_FL_KEEP_SIZE +flag is specified in +.IR mode , +the behavior of the call is similar, +but the file size will not be changed even if +.IR offset + len +is greater than the file size. This behaviour is the same as when +preallocating space with +.B FALLOC_FL_KEEP_SIZE +specified. + +Not all filesystems support +.BR FALLOC_FL_ZERO_RANGE ; +if a filesystem doesn't support the operation, an error is returned. +The operation is supported on at least the following filesystems +.IP * 3 +XFS (since Linux 3.14) +.\" commit 376ba313147b4172f3e8cf620b9fb591f3e8cdfa +.IP * +ext4, for extent based files (since Linux 3.14) +.\" commit b8a8684502a0fc852afa0056c6bb2a9273f6fcc0 + .SH RETURN VALUE On success, .BR fallocate () @@ -243,7 +285,9 @@ no other flags are permitted with .B EINVAL .I mode is -.BR FALLOC_FL_COLLAPSE_RANGE , +.BR FALLOC_FL_COLLAPSE_RANGE +or +.BR FALLOC_FL_ZERO_RANGE, but the file referred to by .I fd is not a regular file. -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
