On Thu, Jan 30, 2014 at 08:42:24PM +0100, Jan Kara wrote: > On Thu 30-01-14 11:57:10, Andreas Dilger wrote: > > On Jan 28, 2014, at 8:48 PM, Zheng Liu <gnehzuil.liu@xxxxxxxxx> wrote: > > > On Tue, Jan 28, 2014 at 03:35:14PM +0100, Jan Kara wrote: > > >> On Tue 28-01-14 14:42:49, Zheng Liu wrote: > > >>> For project quota, the key issue is how to handle link(2)/rename(2). We > > >>> summarize the behaviour in xfs as following. > > >>> > > >>> *Note* > > >>> + unaccounted dir > > >>> x accounted dir > > >>> > > >>> link(2) > > >>> ------- > > >>> + x > > >>> + ok error (EXDEV) > > >>> x ok error (EXDEV) > > > > Presumably this accounted-to-accounted link() is only an error if > > it is between directories of two different projects? > Yes, I understand it that way. Correct. You can have multiple hardlinks within a project, just not across projects. > > >>> rename(2) > > >>> --------- > > >>> + x > > >>> + ok ok > > >>> x wrong ok > > >> > > >> So moving unaccounted file/dir into an accounted dir would be OK? How is > > >> that? > > > > > > Actually xfs will return EXDEV error when we try to move unaccounted > > > file/dir into an accounted dir. Then userspace tools (e.g. mv(1)) will > > > use create(2)/read(2)/write(2) syscalls to create these files/dirs from > > > scratch, and get the same id from their parent. > > > > Why wouldn't renaming an unaccounted file into an accounted directory > > just be implemented by doing the equivalent of chown() to change the > > project ID and setting the quota? That could avoid a HUGE amount of > > data copying for large files. > Well, the trouble is not so much with a file but with a directory. If you > move an unaccounted directory in an accounted dir, you would have to > recursively go through it and account each file. That isn't possible to do > reliably from the kernel... And allowing files but disallowing dirs seems > inconsistent so I'm in favor of a simple API. Even files are problematic. Think of a file with multiple hard links. You can't rename one of those links across to a directory with a different project quota ID for the same reason you can't create hard links across different project ID contexts... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- 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
