Messages in this thread | | | Date | Sun, 12 Oct 2003 00:14:48 -0700 | From | jw schultz <> | Subject | Re: ReiserFS patch for updating ctimes of renamed files |
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On Sun, Oct 12, 2003 at 01:05:19AM -0500, Alex Adriaanse wrote: > Hi, > > I ran into some trouble trying to do incremental backups with GNU tar > (using --listed-incremental) where renaming a file in between backups would > cause the file to disappear upon restoration. When investigating the issue > I discovered that this doesn't happen on ext2, ext3, and tmpfs filesystems > but only on ReiserFS filesystems. I also noticed that for example ext3 > updates the affected file's ctime upon rename whereas ReiserFS doesn't, so > I'm thinking this causes tar to believe that the file existed before the > first backup was taking under the new name, and as a result it doesn't back > it up during the second backup. So I believe ReiserFS needs to update > ctimes for renamed files in order for incremental GNU tar backups to work > reliably. > > I made some changes to the reiserfs_rename function that I *think* should > fix the problem. However, I don't know much about ReiserFS's internals, and > I haven't been able to test them out to see if things work now since I can't > afford to deal with potential FS corruption with my current Linux box. > > I included a patch below against the 2.4.22 kernel with my changes. Would > somebody mind taking a look at this to see if I did things right here (and > perhaps wouldn't mind testing it out either)? If it works then I (and I'm > sure others who've experienced the same problem) would like to see the > changes applied to the next 2.4.x (and 2.6.x?) release.
Hmm. I'm conflicted.
rename(2) manpage: Any other hard links to the file (as created using link(2)) are unaffected.
A change to ctime would affect the other links.
stat(2) manpage: The field st_ctime is changed by writing or by setting inode information (i.e., owner, group, link count, mode, etc.).
I am not aware of any field in the inode structure that must be changed by an atomic rename. Per documentation the only reason rename should update st_ctime is if it does a link+unlink sequence which would alter st_nlink briefly.
On the other hand it does seem to me there ought to be some record that something about the inode changed. st_ctime would be the only appropriate indicator.
rename() SUSv3: Some implementations mark for update the st_ctime field of renamed files and some do not. Applications which make use of the st_ctime field may behave differently with respect to renamed files unless they are designed to allow for either behavior.
So reiserfs is on this point definitely standards conformant already. A change could at best be seen as an enhancement.
-- ________________________________________________________________ J.W. Schultz Pegasystems Technologies email address: jw@pegasys.ws
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