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The meaning of PTR_TO_BTF_ID_OR_NULL differs slightly from other types denoted with the *_OR_NULL type. For example the types PTR_TO_SOCKET and PTR_TO_SOCKET_OR_NULL can be used for branch analysis because the type PTR_TO_SOCKET is guaranteed to _not_ have a null value. In contrast PTR_TO_BTF_ID and BTF_TO_BTF_ID_OR_NULL have slightly different meanings. A PTR_TO_BTF_TO_ID may be a pointer to NULL value, but it is safe to read this pointer in the program context because the program context will handle any faults. The fallout is for PTR_TO_BTF_ID the verifier can assume reads are safe, but can not use the type in branch analysis. Additionally, authors need to be extra careful when passing PTR_TO_BTF_ID into helpers. In general helpers consuming type PTR_TO_BTF_ID will need to assume it may be null. Seeing the above is not obvious to readers without the back knowledge lets add a comment in the type definition. Editorial comment, as networking and tracing programs get closer and more tightly merged we may need to consider a new type that we can ensure is non-null for branch analysis and also passing into helpers. Signed-off-by: John Fastabend <john.fastabend@gmail.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Lorenz Bauer <lmb@cloudflare.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.