Allow repeated readdir offsets #581
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POSIX allows seeking an open directory handle, which in FUSE means the `offset` can be any offset we've previously returned. This is pretty annoying for us to implement since we're streaming directory entries from S3 with ListObjects, which can't resume from an arbitrary index, and can't fit its continuation tokens into a 64-bit offset anyway. So we're probably never going to truly support seeking a directory handle. But there's a special case we've seen come up a couple of times (awslabs#477, awslabs#520): some applications read one page of directory entries and then seek back to 0 and do it again. I don't fully understand _why_ they do this, but it's common enough that it's worth special casing. This change makes open directory handles remember their most recent response so that they can repeat it if asked for the same offset again. It's not too complicated other than needing to make sure we do readdirplus correctly (managing the lookup counts for entries that are being returned a second time). I've tested this by running the PHP example from awslabs#477, which now works. Signed-off-by: James Bornholt <bornholt@amazon.com>
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dannycjones
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Signed-off-by: James Bornholt <bornholt@amazon.com>
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Description of change
POSIX allows seeking an open directory handle, which in FUSE means the
offsetcan be any offset we've previously returned. This is prettyannoying for us to implement since we're streaming directory entries
from S3 with ListObjects, which can't resume from an arbitrary index,
and can't fit its continuation tokens into a 64-bit offset anyway. So
we're probably never going to truly support seeking a directory handle.
But there's a special case we've seen come up a couple of times (#477, #520):
some applications read one page of directory entries and then seek back
to 0 and do it again. I don't fully understand why they do this, but
it's common enough that it's worth special casing.
This change makes open directory handles remember their most recent
response so that they can repeat it if asked for the same offset again.
It's not too complicated other than needing to make sure we do
readdirplus correctly (managing the lookup counts for entries that are
being returned a second time).
I've tested this by running the PHP example from #477, which now works.
Related issues: fixes #477, fixes #520.
Does this change impact existing behavior?
No, it allows a case to succeed that previously failed.
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and I agree to the terms of the Developer Certificate of Origin (DCO).