On Mon, Jun 02, 2014 at 03:06:13PM +0200, Lukáš Czerner wrote: > > > So what will happen when there is not enough space when "inserting a > > > range" ? And how should user proceed from there ? > > If insert range fails with an ENOSPC error, user could use collapse > > range on the same range to remove the hole. > > And after freeing more space, he can again try inserting range. > > Ofcourse, this type of guidance should be properly documented in > > manpage. When updating fallocate(2) manpage, I will keep in mind to > > describe ENOSPC handling. > > Why collapse ? The hole is already there right ? Why not just use > fallocate to allocate the space for the hole. And that's my point > actually. Why not do it this way in the first place, because this is > really counterintuitive. It's worse than that. It's possible that the reason why you got the ENOSPC warning was because the operation to move the extents down required allocating a block, and it was *that* block allocation which failed. So it's not deterministic whether or not the file's extent mappings were modified after a ENOSPC error, and so it's not clear whether or not a collapse_range function will undo the range that had been inserted --- or whether it ends up deleting existing data blocks. In generally, you really want system calls to have all-or-nothing effects, where if the system call returns an error, the state of the file has not been changed. And for that reason, I agree with Lukáš that it is really a good idea to decouple moving the blocks down, and allocating space --- and to make sure that if there is any failure while inserting the range, the state of the file is not modified at all. Cheers, - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
