Christopher Collins created MYNEWT-555:
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Summary: BLE Host - Avoid mbuf copy on chr read
Key: MYNEWT-555
URL: https://issues.apache.org/jira/browse/MYNEWT-555
Project: Mynewt
Issue Type: Bug
Components: Nimble
Reporter: Christopher Collins
Assignee: Christopher Collins
Fix For: v1_0_0_rel
When the host receives any form of characteristic read request, an extraneous
mbuf gets allocated. The sequence is:
* Allocate new mbuf.
* Pass new mbuf to application code so app can fill in characteristic value.
* Copy characteristic value out of new mbuf into response mbuf
* Free new mbuf
The reason for the extra allocation is to simplify reads that specify non-zero
offsets. In the case of a GATT read, the peer may read from different offsets
of the characteristic. In an effort to simplify the API, I decided the
requested offset should be hidden from the application. Instead, the
application always provides the full characteristic value, and the host copies
the requested portion out of the user-filled mbuf and into the ACL data packet.
The fix is to try to reuse the response to hold the characteristic data. This
can be done if the read request specifies an offset of 0. For non-zero
offsets, the old behavior remains: allocate an extra mbuf and copy the data.
Additional context:
https://lists.apache.org/thread.html/78358745716cac9512b3c659dfe9b9b7bbb1354ee4c38d6da137bcc0@%3Cdev.mynewt.apache.org%3E
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