Re: [PATCH v3] fallocate.2: Document FALLOC_FL_ZERO_RANGE

["Michael Kerrisk (man-pages)" <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> ---
> 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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