Rust-for-Linux
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@@ -298,3 +298,48 @@ A: NO.
 
 The BTF_ID macro does not cause a function to become part of the ABI
 any more than does the EXPORT_SYMBOL_GPL macro.
+
+Q: What is the compatibility story for special BPF types in map values?
+-----------------------------------------------------------------------
+Q: Users are allowed to embed bpf_spin_lock, bpf_timer fields in their BPF map
+values (when using BTF support for BPF maps). This allows to use helpers for
+such objects on these fields inside map values. Users are also allowed to embed
+pointers to some kernel types (with __kptr and __kptr_ref BTF tags). Will the
+kernel preserve backwards compatibility for these features?
+
+A: It depends. For bpf_spin_lock, bpf_timer: YES, for kptr and everything else:
+NO, but see below.
+
+For struct types that have been added already, like bpf_spin_lock and bpf_timer,
+the kernel will preserve backwards compatibility, as they are part of UAPI.
+
+For kptrs, they are also part of UAPI, but only with respect to the kptr
+mechanism. The types that you can use with a __kptr and __kptr_ref tagged
+pointer in your struct are NOT part of the UAPI contract. The supported types can
+and will change across kernel releases. However, operations like accessing kptr
+fields and bpf_kptr_xchg() helper will continue to be supported across kernel
+releases for the supported types.
+
+For any other supported struct type, unless explicitly stated in this document
+and added to bpf.h UAPI header, such types can and will arbitrarily change their
+size, type, and alignment, or any other user visible API or ABI detail across
+kernel releases. The users must adapt their BPF programs to the new changes and
+update them to make sure their programs continue to work correctly.
+
+NOTE: BPF subsystem specially reserves the 'bpf\_' prefix for type names, in
+order to introduce more special fields in the future. Hence, user programs must
+avoid defining types with 'bpf\_' prefix to not be broken in future releases.
+In other words, no backwards compatibility is guaranteed if one using a type
+in BTF with 'bpf\_' prefix.
+
+Q: What is the compatibility story for special BPF types in allocated objects?
+------------------------------------------------------------------------------
+Q: Same as above, but for allocated objects (i.e. objects allocated using
+bpf_obj_new for user defined types). Will the kernel preserve backwards
+compatibility for these features?
+
+A: NO.
+
+Unlike map value types, there are no stability guarantees for this case. The
+whole API to work with allocated objects and any support for special fields
+inside them is unstable (since it is exposed through kfuncs).
@@ -44,6 +44,33 @@ is a guarantee that the reported issue will be overlooked.**
 Submitting patches
 ==================
 
+Q: How do I run BPF CI on my changes before sending them out for review?
+------------------------------------------------------------------------
+A: BPF CI is GitHub based and hosted at https://github.com/kernel-patches/bpf.
+While GitHub also provides a CLI that can be used to accomplish the same
+results, here we focus on the UI based workflow.
+
+The following steps lay out how to start a CI run for your patches:
+
+- Create a fork of the aforementioned repository in your own account (one time
+  action)
+
+- Clone the fork locally, check out a new branch tracking either the bpf-next
+  or bpf branch, and apply your to-be-tested patches on top of it
+
+- Push the local branch to your fork and create a pull request against
+  kernel-patches/bpf's bpf-next_base or bpf_base branch, respectively
+
+Shortly after the pull request has been created, the CI workflow will run. Note
+that capacity is shared with patches submitted upstream being checked and so
+depending on utilization the run can take a while to finish.
+
+Note furthermore that both base branches (bpf-next_base and bpf_base) will be
+updated as patches are pushed to the respective upstream branches they track. As
+such, your patch set will automatically (be attempted to) be rebased as well.
+This behavior can result in a CI run being aborted and restarted with the new
+base line.
+
 Q: To which mailing list do I need to submit my BPF patches?
 ------------------------------------------------------------
 A: Please submit your BPF patches to the bpf kernel mailing list: