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bpf: Document BPF_PROG_PIN syscall command

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Commit b2197755b2 ("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 6d8cb045cd
("bpf: comment why dots in filenames under BPF virtual FS are not allowed")

Signed-off-by: Joe Stringer <joe@cilium.io>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210302171947.2268128-5-joe@cilium.io
This commit is contained in:
Joe Stringer 2021-03-02 09:19:36 -08:00 committed by Alexei Starovoitov
parent 6690523bcc
commit 8aacb3c8d1
1 changed files with 29 additions and 7 deletions
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36
include/uapi/linux/bpf.h
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@ -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,