On Fri, 18 Apr 2014, Michael Kerrisk (man-pages) wrote: > Date: Fri, 18 Apr 2014 17:49:48 +0200 > From: "Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx> > To: Lukas Czerner <lczerner@xxxxxxxxxx> > Cc: mtk.manpages@xxxxxxxxx, linux-man@xxxxxxxxxxxxxxx, > linux-fsdevel@xxxxxxxxxxxxxxx > Subject: Re: [PATCH] fallocate.2: Document FALLOC_FL_ZERO_RANGE > > Lukas, > > Thanks for the patch. > > Two general comments: > * The text does not explain what zeroing file space is about and why one > would do it. For example, I'm a little unclear after reading it whether > FALLOC_FL_ZERO_RANGE will create a hole in a file. It is saying that blocks are preallocated for the regions that span holes in the file. And there isn't anything saying about punching a hole into the file. But I guess I can be more clear about it. > * Some entries should probably be added to ERRORS. > > Could you fix both of those and resubmit? Sure I'll do that next week. > > Note that I've just pushed some changes to the page for > FALLOC_FL_COLLAPSE_RANGE, so you may want to pull the latest version to > ensure there are no conflicts. > > Cheers, > > Michael > > > On 04/17/2014 03:30 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> > > --- > > man2/fallocate.2 | 41 +++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 41 insertions(+) > > > > diff --git a/man2/fallocate.2 b/man2/fallocate.2 > > index b31bbde..df31782 100644 > > --- a/man2/fallocate.2 > > +++ b/man2/fallocate.2 > > @@ -124,6 +124,45 @@ Btrfs (since Linux 3.7) > > .IP * > > tmpfs (since Linux 3.5) > > .\" commit 83e4fa9c16e4af7122e31be3eca5d57881d236fe > > +.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. > > + > > +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 2.14) > > +.\" commit 376ba313147b4172f3e8cf620b9fb591f3e8cdfa > > +.IP * > > +ext4 (since Linux 3.14) > > +.\" commit b8a8684502a0fc852afa0056c6bb2a9273f6fcc0 > > .SH RETURN VALUE > > On success, > > .BR fallocate () > > @@ -193,6 +232,8 @@ Or: > > .I mode > > specifies > > .BR FALLOC_FL_PUNCH_HOLE > > +or > > +.BR FALLOC_FL_ZERO_RANGE > > and > > the file referred to by > > .I fd > > > > > -- 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
