Sam Lang wrote:
On Dec 19, 2005, at 6:07 PM, Rob Ross wrote:
I don't consider rmdirent to be a case that we need to highly
optimize, so if it helps to lookup the name and do the getattr
beforehand, that's cool by me. I'm sure somewhere out there there is
a rmdir test that we'll do a little worse on, but whatever.
You'll still have to getattr again after the rmdirent to make sure
that the directory is still empty though, in case someone sneaks in
between the first getattr and the rmdirent and creates something.
I think I can just check if the directory is not empty. If the getattr
tells me it is empty, I just do the remove, and if someone else has
added an entry in the meantime, I'll get the ENOTOEMPTY from the server
at that point, so I can go add the entry back in to the parent (which is
what we do now).
So by this you mean to just check once, before the rmdirent, to see if
it is empty. I agree; I proposed adding an unnecessary operation.
Side note to Murali: if we had vtags here, we could avoid the race :).
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
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