On Tue, Feb 25, 2014 at 03:41:28PM -0800, Andrew Morton wrote: > On Tue, 25 Feb 2014 15:23:35 -0800 (PST) Hugh Dickins <hughd@xxxxxxxxxx> wrote: > > On Tue, 25 Feb 2014, Dave Chinner wrote: > > > On Tue, Feb 25, 2014 at 02:16:01PM +1100, Stephen Rothwell wrote: > > > > On Mon, 24 Feb 2014 11:57:10 +1100 Dave Chinner <david@xxxxxxxxxxxxx> wrote: > > FALLOC_FL_COLLAPSE_RANGE: I'm a little sad at the name COLLAPSE, > > but probably seven months too late to object. It surprises me that > > you're doing all this work to deflate a part of the file, without > > the obvious complementary work to inflate it - presumably all those > > advertisers whose ads you're cutting out, will come back to us soon > > to ask for inflation, so that they have somewhere to reinsert them ;) > > Yes, I was wondering that. Why not simply "move these blocks from here > to there". And open a completely unnecessary can of worms to do with behavioural and implementation corner cases? Do you allow it to destroy data by default? Or only allow moves into holes? What do you do with range the data is moved out of? Does it just become a hole? What happens if the range overlaps EOF - does that change the file size? What if you want to move the range beyond EOF? What if the source and destination ranges overlap? What happens when you move the block at EOF into the middle of a file - do you end up with zeros padding the block and the file size having to be adjusted accordingly? Or do we have to *copy* all the data in high blocks down to fill the hole in the block? What behaviour should we expect if the filesystem can't implement the entire move atomically and we crash in the middle of the move? I can keep going, but I'll stop here - you get the idea. In comparison, collapse range as a file data manipulation has very specific requirements and from that we can define a simple, specific API that allows filesystems to accelerate that operation by extent manipulation rather than read/memcpy/write that the applications are currently doing for this operation.... IOWs, collapse range is a simple operation, "move arbitrary blocks from here to there" is a nightmare both from the specification and the implementation points of view. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
