On Thu, 21 Dec 2006, Jan Harkes wrote:
On Wed, Dec 20, 2006 at 12:44:42PM +0100, Miklos Szeredi wrote:
The stat64.st_ino field is 64bit, so AFAICS you'd only need to extend
the kstat.ino field to 64bit and fix those filesystems to fill in
kstat correctly.
Coda actually uses 128-bit file identifiers internally, so 64-bits
really doesn't cut it. Since the 128-bit space is used pretty sparsely
there is a hash which avoids most collistions in 32-bit i_ino space, but
not completely. I can also imagine that at some point someone wants to
implement a git-based filesystem where it would be more natural to use
160-bit SHA1 hashes as unique object identifiers.
But Coda only allow hardlinks within a single directory and if someone
renames a hardlinked file and one of the names ends up in a different
directory we implicitly create a copy of the object. This actually
leverages off of the way we handle volume snapshots and the fact that we
use whole file caching and writes, so we only copy the metadata while
the data is 'copy-on-write'.
The problem is that if inode number collision happens occasionally, you
get data corruption with cp -a command --- it will just copy one file and
hardlink the other.
Any application that tries to be smart enough to keep track of which
files are hardlinked should (in my opinion) also have a way to disable
this behaviour.
If user (or script) doesn't specify that flag, it doesn't help. I think
the best solution for these filesystems would be either to add new syscall
int is_hardlink(char *filename1, char *filename2)
(but I know adding syscall bloat may be objectionable)
or add new field in statvfs ST_HAS_BROKEN_INO_T, that applications can
test and disable hardlink processing.
Mikulas
Jan
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