readdir() ordering guarantees on XFS

dizzy
2008-06-06T13:34:26Z

Hello

POSIX leaves unspecified the order of getting the entries with readdir(). This
is normal since different filesystems may implement their own techniques to
organize entries in a directory (linear, hash, various search trees, etc).

But if I can makes sure that several Linux machines will have the same FS (ie
XFS), mount options and same kernels can assume that traversing the same file
hierarchy structure (that is a file structure with the exact same directories
and files as names, structure, attributes, except maybe "ctime" which we
can't really control in Linux) can I expect that traversing using readdir()
will give me the entries in the exact same order? Or are there any other
conditions that I have to check for that would guarantee it? (such as, for a
linear directory aproach one has to have created the directory entries in the
same order on all the machines to expect same order on readdir()).

Currently, we workaround this issue by reading all the directory entries,
sorting them and traversing the entries in the sorted order. This however has
been proven to slow the traversal (depth first traversal) operation about 30%
than doing it in the order received from readdir() (I even had the test code
read the whole directory contents, sort them in memory but still have it
traverse in the order readdir() reported and it is 30% faster than traversing
in the sorted order).

Any idea?

Thanks!

PS: please Cc: me as I'm not subscribed to the list, thank you

--
Mihai RUSU Email: dizzy@roedu.net
"Linux is obsolete" -- AST