Hi, On 23 Oct 2007, at 08:53, Barry Naujok wrote:
Following is the initial test version of case-insensitive support for XFS in Linux. It implements case-insensitivity utilising a Unicode case folding table stored on disk generated from http://www.unicode.org/Public/UNIDATA/CaseFolding.txt As the filesystem stores names as Unicode (UTF-8), the "nls" mount option has been added to support systems not utilising UTF-8 natively. If the nls mount option is not used, it will use the default NLS defined in the kernel's config. To allow case-insensitivity to be a mount option rather than a mkfs option, the hashes stored on disk are always case-folded. This is indicated by the new "unicode" bit in the superblock. This bit also associated with the presence of the case-folding table on disk. With the case-folding table on disk, it allows us to upgrade the table in the future while retaining backwards and forwards compatibility. It also allows special case tables such as Turkic case which is supported in this patch set. The case-insensitive support also installs a couple of dentry_operations for the XFS inodes: hash and compare. Currently, there is a couple of outstanding issues with the dentry cache interaction: - The first lookup if case-mismatched will continue to have the mismatched case in the cache. Not really sure if this is an issue or not. If it is an issue, how should I resolve it? - As above, but with a non-existing lookup, then creating the file with a different case, the first failed lookup will define the case used. I have partially resolved this with a memcpy if the two lengths are the same. How do I fix this if the lengths are different? (TODO's show the location of this problem.)
Both of the above can be fairly easily fixed if you want. NTFS does it in the stock kernel.
You would need to change the XFS ->lookup inode operation so that when it reads the directory to check whether a name exists, if it is found but the case is not matched, you need to make a copy of the correctly cased name (if NTFS this is done in fs/ntfs/ dir.c::ntfs_lookup_inode_by_name() if you want to take a look, the name is stored in the "ntfs_name" structure that is allocated during the lookup if a case mismatched match is found and this is returned to the caller).
Then in ->lookup() if you got a correctly cased name structure (if the name was cased correctly the correctly cased named structure pointer would be NULL) then you need to replace the dentry passed into - >lookup with a new one with the correct case. This is a little complicated because such a dentry may already exist in which case you have to use the existing one (instantiating it if it was negative) and if it does not already exist you need to allocate a new one, instantiate it and then move it over the old one. Again a little complicated because of disconnected dentries for NFS. But it is not too bad and it works well in NTFS (see fs/ntfs/namei.c::ntfs_lookup() the code that does all of this starts at the "handle_name" goto label).
Doing things this way means that you never have wrong case dentries in dcache. And this in turn means that things like handling ->unlink and ->rename inode operations is much easier as the dentry you receive there is returned from a ->lookup() call thus you know it is correctly cased already so you can do a case-sensitive match when looking up the directory entry to remove/rename! (I am afraid you cannot look at the NTFS code for that as that is not publicly available yet. )-:)
Best regards, Anton
Other TODOs: - support for case-insensitve extended attributes as a separate mount option. - Other xfsprogs updates: xfs_repair, xfs_db
-- Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @) Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK Linux NTFS maintainer, http://www.linux-ntfs.org/ - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
