Hi all, As discussed with ext4 folks, I will try to make ext4 file system support directory quota (a.k.a., project id in xfs). For keeping consistency with xfs's implementation, I did some tests on xfs, and I summarized the result as following. This will help us understand what we can do and what we can't do. Please correct me if I miss doing some tests or mis- understand something. I just do some tests about rename/hardlink because they are the key issue from our discussion. + unaccounted dir x accounted dir rename(mv) ========== + -> +: ok + -> x: ok I use strace(1) to lookup which syscall is used, and I found that xfs will return EXDEV when mv(1) tries to use rename(2) to move a dir from a unaccounted dir to a accounted dir. Then mv uses creat(2)/read(2)/ write(2) syscalls to move this dir. x -> +: wrong (design by feature?) If we move a dir from a accounted dir to a unaccounted dir, the quota is still accounted. It seems that xfs don't remove project id from this dir and its subdirs/files on this case. x -> x: ok Xfs returns EXDEV error when mv(1) uses rename(2) to move a dir from a accounted dir to another accounted dir (These dirs have different project ids). Then mv(1) uses creat(1)/read(1)/write(1) syscalls to move this dir. summary: rename + x + ok ok (EXDEV) x wrong ok (EXDEV) hardlink(ln) ======== + -> +: ok + -> x: error Xfs also returns EXDEV error to forbid this operation. So that means that we don't allow users to do a hardlink for a file from a unaccount dir to a accounted dir. x -> +: ok This operation can be executed and no any error is reported. After that the quota doesn't be changed. When both of two hardlinks are removed, the quota will be discharged. x -> x: error Xfs returns EXDEV error to forbid this operation. summary: hardlink + x + ok error (EXDEV) x ok error (EXDEV) As always, any comment or idea are welcome. Thanks, - Zheng -- 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
