@@ -219,6 +219,22 @@ union bpf_iter_link_info {
* Pin an eBPF program or map referred by the specified *bpf_fd*
* to the provided *pathname* on the filesystem.
*
+ * The *pathname* argument must not contain a dot (".").
+ *
+ * On success, *pathname* retains a reference to the eBPF object,
+ * preventing deallocation of the object when the original
+ * *bpf_fd* is closed. This allow the eBPF object to live beyond
+ * **close**\ (\ *bpf_fd*\ ), and hence the lifetime of the parent
+ * process.
+ *
+ * Applying **unlink**\ (2) or similar calls to the *pathname*
+ * unpins the object from the filesystem, removing the reference.
+ * If no other file descriptors or filesystem nodes refer to the
+ * same object, it will be deallocated (see NOTES).
+ *
+ * The filesystem type for the parent directory of *pathname* must
+ * be **BPF_FS_MAGIC**.
+ *
* Return
* Returns zero on success. On error, -1 is returned and *errno*
* is set appropriately.
@@ -584,13 +600,19 @@ union bpf_iter_link_info {
*
* NOTES
* eBPF objects (maps and programs) can be shared between processes.
- * For example, after **fork**\ (2), the child inherits file descriptors
- * referring to the same eBPF objects. In addition, file descriptors
- * referring to eBPF objects can be transferred over UNIX domain sockets.
- * File descriptors referring to eBPF objects can be duplicated in the
- * usual way, using **dup**\ (2) and similar calls. An eBPF object is
- * deallocated only after all file descriptors referring to the object
- * have been closed.
+ *
+ * * After **fork**\ (2), the child inherits file descriptors
+ * referring to the same eBPF objects.
+ * * File descriptors referring to eBPF objects can be transferred over
+ * **unix**\ (7) domain sockets.
+ * * File descriptors referring to eBPF objects can be duplicated in the
+ * usual way, using **dup**\ (2) and similar calls.
+ * * File descriptors referring to eBPF objects can be pinned to the
+ * filesystem using the **BPF_OBJ_PIN** command of **bpf**\ (2).
+ *
+ * An eBPF object is deallocated only after all file descriptors referring
+ * to the object have been closed and no references remain pinned to the
+ * filesystem or attached (for example, bound to a program or device).
*/
enum bpf_cmd {
BPF_MAP_CREATE,
Commit b2197755b263 ("bpf: add support for persistent maps/progs") contains the original implementation and git logs, used as reference for this documentation. Also pull in the filename restriction as documented in commit 6d8cb045cde6 ("bpf: comment why dots in filenames under BPF virtual FS are not allowed") Acked-by: Toke Høiland-Jørgensen <toke@redhat.com> Reviewed-by: Quentin Monnet <quentin@isovalent.com> Signed-off-by: Joe Stringer <joe@cilium.io> --- CC: Daniel Borkmann <daniel@iogearbox.net> --- include/uapi/linux/bpf.h | 36 +++++++++++++++++++++++++++++------- 1 file changed, 29 insertions(+), 7 deletions(-)