On Mon, 5 May 2014, Michael Kerrisk (man-pages) wrote: > Date: Mon, 05 May 2014 14:44:48 +0200 > From: "Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx> > To: Lukas Czerner <lczerner@xxxxxxxxxx> > Cc: mtk.manpages@xxxxxxxxx, linux-man@xxxxxxxxxxxxxxx > Subject: Re: [PATCH v3] fallocate.2: Document FALLOC_FL_ZERO_RANGE > > > 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. mostly for metadata as mentioned in my patch. Because we still need to manually zero out partial blocks. But that's not really all that important. So I think it look ok. Thanks! -Lukas > > 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 >
