On 17-07-06 03:03 PM, Jason Dillaman wrote:
On Thu, Jul 6, 2017 at 8:26 AM, Piotr Dałek <piotr.dalek@xxxxxxxxxxxx> wrote:
Hi,
If you're using "rbd_aio_write()" in your code, be aware of the fact that
before Luminous release, this function expects buffer to remain unchanged
until write op ends, and on Luminous and later this function internally
copies the buffer, allocating memory where needed, freeing it once write is
done.
Pre-Luminous also copies the provided buffer when using the C API --
it just copies it at a later point and not immediately. The eventual
goal is to eliminate the copy completely, but that requires some
additional plumbing work deep down within the librados messenger
layer.
I've learned the hard way that pre-luminous, even if it copies the buffer,
it does so too late. In my specific case, my FUSE module does enter the
write call and issues rbd_aio_write there, then exits the write - expecting
the buffer provided by FUSE to be copied by librbd (as it happens now in
Luminous). I didn't expect that it's a new behavior and once my code was
deployed to use Jewel librbd, it started to consistently corrupt data during
write.
--
Piotr Dałek
piotr.dalek@xxxxxxxxxxxx
https://www.ovh.com/us/
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