I thought we wanted (3,4) before (2)?
Rob
Sam Lang wrote:
So I have something that does what I think we want for remove. It
basically does the following steps. Note that the difference from
before is that steps 1 and 4 have been added:
1. check ncache and acache for name/attr and then check dirent_count !=
0 -> return ENOTEMPTY.
2. rmdirent(name) => object
3. getattr(object) => attr
4. if attr.dirent_count != 0, do crdirent and return ENOTEMPTY
5. remove(object) => if returns ENOTEMPTY, do crdirent and return
ENOTEMPTY
Also, the directory name => object mapping was getting invalidated in
the name cache at cleanup even with ENOTEMPTY. I've added a check to
only invalidate if we're not returning ENOTEMPTY.
Does this look reasonable to everyone?
-sam
On Dec 19, 2005, at 10:33 PM, Rob Ross wrote:
Ok, I was missing your point before, but I get it now -- if we were to
put the new getattr in before the rmdirent, there is a possibility
that someone could remove the last entry in the directory after the
getattr but before the rmdirent could happen.
It's not a race though. A race has to have unexpected results based
on relative timing. In our case, the situation you describe is
indistinguishable from the case where the final removal occurs just as
the rmdir returns, which is fine.
This new scheme does still leave open the possibility that we remove a
directory's dirent when there is something in the directory (and then
we recreate the dirent). We're just reducing the opportunities for
this being seen.
It is also not the case that vtags would help here, because the
directory's dirent (which is what we remove first) is not part of the
directory itself (which is what we'd have the vtag for). I'm batting
like 100 or so tonight, so I think I'll quit writing emails after this
one and go to sleep or something.
Rob
Rob Ross wrote:
Sam Lang wrote:
The race that's an issue seems to be if the getattr tells me the
directory is not empty, in which case I just return ENOTEMPTY back
to the caller, but in the meantime someone else could have removed
all the entries (in which case the remove should have succeeded).
I'm not sure that's much of an issue for our users though.
That's not a race. First thing that happens on a file removal is
that the directory entry is removed, so if something is being
removed, it won't be in the directory.
Right now our caching scheme is under-the-covers so to speak, where
we always continue with the operation if the cache misses. It seems
like we could make a decision based on a cache hit. In other words,
if I know the name and attribute are cached, I can save time by
checking if the directory is not empty. If its not cached, I can
just go down the rmdirent path like we do now. Doing lookup/getattr
will add an extra roundtrip in most cases (where the directory is
empty) if things aren't being cached. Overkill?
I don't like caching negative entries without consistency, so I like
the idea of going down the path if we don't have any directory
contents cached.
Rob
_______________________________________________
PVFS2-developers mailing list
[email protected]
http://www.beowulf-underground.org/mailman/listinfo/pvfs2-developers
_______________________________________________
PVFS2-developers mailing list
[email protected]
http://www.beowulf-underground.org/mailman/listinfo/pvfs2-developers
