KFunc bpf_rdonly_cast
Definition
This kfunc tries to cast the object to a specified type.
The function returns the same obj but with PTR_TO_BTF_ID with
btf_id. The verifier will ensure btf_id being a struct type.
Since the supported type cast may not reflect what the 'obj'
represents, the returned btf_id is marked as PTR_UNTRUSTED, so
the return value and subsequent pointer chasing cannot be
used as helper/kfunc arguments.
void *bpf_rdonly_cast(const void *obj__ign, u32 btf_id__k)
signature changed
The signature of this kfunc has changed in v6.9. The previous signature was void *bpf_rdonly_cast(void *obj__ign, u32 btf_id__k) weak ELF symbols can be used to support both versions.
Usage
This tries to support use case like below:
#define skb_shinfo(SKB) ((struct skb_shared_info *)(skb_end_pointer(SKB)))
where skb_end_pointer(SKB) is a unsigned char * and needs to
be casted to struct skb_shared_info *.
Program types
The following program types can make use of this kfunc:
BPF_PROG_TYPE_CGROUP_SKBBPF_PROG_TYPE_CGROUP_SOCK_ADDRBPF_PROG_TYPE_LSMBPF_PROG_TYPE_LWT_INBPF_PROG_TYPE_LWT_OUTBPF_PROG_TYPE_LWT_SEG6LOCALBPF_PROG_TYPE_LWT_XMITBPF_PROG_TYPE_NETFILTERBPF_PROG_TYPE_SCHED_ACTBPF_PROG_TYPE_SCHED_CLSBPF_PROG_TYPE_SK_SKBBPF_PROG_TYPE_SOCKET_FILTERBPF_PROG_TYPE_STRUCT_OPSBPF_PROG_TYPE_SYSCALLBPF_PROG_TYPE_TRACINGBPF_PROG_TYPE_XDP
Example
Docs could be improved
This part of the docs is incomplete, contributions are very welcome