On 05/05/2014 02:04 PM, Lukas Czerner wrote:
> 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
Thank, Lukáš.
In fact I'd already merged and tweaked your previous patch into
a branch, and the only new piece from this patch that I needed
was the piece about ext4 extent-based files.
The text now reads:
Zeroing file space
Specifying the FALLOC_FL_ZERO_RANGE flag (available since Linux
3.14) in mode zeroes space in the byte range starting at offset
and continuing for 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 filesystem preferably by converting
the range into unwritten extents. This approach means that the
specified range will not be physically zeroed out on the
device, and I/O is required only to update file metadata.
If the FALLOC_FL_KEEP_SIZE flag is additionally specified in
mode, the behavior of the call is similar, but the file size
will not be changed even if offset+len is greater than the file
size. This behaviour is the same as when preallocating space
with FALLOC_FL_KEEP_SIZE specified.
Not all filesystems support FALLOC_FL_ZERO_RANGE; if a filesys‐
tem doesn't support the operation, an error is returned. The
operation is supported on at least the following filesystems:
* XFS (since Linux 3.14)
* ext4, for extent-based files (since Linux 3.14)
...
ERRORS
EINVAL mode is FALLOC_FL_COLLAPSE_RANGE or FAL‐
LOC_FL_ZERO_RANGE, but the file referred to by fd is not
a regular file.
Okay?
Cheers,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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