[PATCH proxmox v9 0/5] add proxmox-ebpf library

[Hannes Laimer <h.laimer@proxmox.com>]

proxmox-ebpf allows working with the BPF kernel state, it also handles
the loading of new programs and the pinning of them and the maps they
reference. It keeps track of map layouts currently loaded, and handles
the locking of concurrent updates to maps. And it offers an interface to
attach or detach programs to interfaces and fill the maps they
reference.

It places the pins in the following directory structure
```
/sys/fs/bpf/proxmox-ebpf/<subsystem>
    links/
    <schema-version>/
        live/
            <map_1>
            prog/
                <direction>
        staging/
            .. like live
```
This allows it to keep maps and programs that have a different schema
version strictly apart. With this we also make sure processes running
stale versions never interact with maps that they don't know the layout
of.

Program object files with the definitions of their maps are shipped as
a separate package, and this library expects them to be placed under
`/usr/lib/proxmox-ebpf/<subsystem>.bpf.o`. These shipped object files
have to have their schema version in the `.proxmox.schema` ELF section.
`/usr/lib/proxmox-ebpf/order` sets the order the programs of the
subsystems run in on an interface. A change to it only affects attaches.
Program and schema updates only swap the program of a link, so every
link keeps its place in the run-order.

All of this is covered in more detail in the doc sections of the two
modules.


v9, thanks a lot @Thomas and @Wolfgang!:
 * move BPF object files into their own package, this means all the C
   handling stuff left the lib. we now expect the object files under
   `/usr/lib/proxmox-ebpf/<subsystem>.bpf.o`
 * the order file is also shipped with the object files, and is expected
   under `/usr/lib/proxmox-ebpf/order`
 * fingerprint of the object binaries was also dropped, we now assume
   the object files present on the host are current, so dependency
   management of program versions is handled through debian packaging
 * the schema version of a subsystem is now part of the object files
   holding the programs and maps, it is in the `.proxmox.schema` ELF
   section. the library only loads/interacts with object files that
   have a matching schema-version, so on a map layout change both the
   package shipping the object and the rust subsystem running it have to
   bump their version
 * use proxmox-sys's locking instead of polling
 * improve docs
 * check map type on load

v8:
 * include map names and directions in program fingerprint in addition
   to the object
 * the repair after an interrupted replacement only moves links onto
   programs the live set has, it does not detach links of a direction
   the new build dropped before the new build is in, that broke a
   replace that died while staging and then failed its fill
 * include pkg version in order file, a newer build will seed the list
   and merge the existing one in, an older build will merge its list
   into the existing one. this solves the problem of whatever build is
   run first seeds the order list at boot, basically making it random
 * add missing context to err

v7:
 * include rust pkg version next to fingerprint, so we can avoid
   flip-flopping the loaded programs in case a worker stays around
   during/after an upgrade
 * differentiate between a link swap failing on open or on the swap
   itself
 * replacing the maps and clearing take the lock guard mutably, so a map
   ref opened before cannot be written after the exchange, it would hit
   the retired map
 * the repair after an interrupted replacement also detaches the links
   of a direction the update dropped, a retry that failed afterwards
   left them attached
 * add context to io errors
 * merge a run order change, don't blindly replace, this covers cases
   where something was added and reordered in one

v6:
 * loop all links at the start of every replace, moving links to live/
   is done one-by-one, so it can fail. a failed pass then has some links
   still on staging/, this makes sure we don't delete state that may
   still be attached. the kernel checks if it already exists on a swap,
   so this is a no-op, and at worst an atomic swap for links that still
   have staging/ attached
 * only allow adding to the run order, at least for live updates.
   removal or re-orders are applied on the next reboot
 * enforce that map refs live as long as the lock they were taken under
 * a pin that cannot be opened stays and fails the step instead of
   being unlinked, which under a descriptor shortage detached a working
   link
 * the harness tests run a C program of their own against the shim
 * move the crate into the proxmox workspace, the vendored vmlinux.h is
   gone, the programs build against the UAPI headers of
   proxmox-kernel-libc-dev with a versioned clang

v5:
 * add a call that replaces the maps as a whole, it uses more space and
   writes everything instead of only what changed, but leaves the old
   content in place instead of a mix, in cases where the write fails
   with ENOMEM. Subsystems choose which they need
 * install/upgrade now also use this newly added replace path, this
   simplifies the process and also closes a hole where attached programs
   would read empty maps, shortly before they were filled after a schema
   version bump
 * the run order of the subsystems is written to
   `/run/proxmox-ebpf/order` by a full apply and every attach places by
   it, so a stale process running an older version attaches correctly
   against subsystems added by a process running a newer version
 * set correct permissions on `/run/..`
 * a build whose schema is older than the pinned one no longer counts
   its state as current, so its single steps back off as well
 * add `interrupted()` on the lock guard, true when a replacement left
   its staged set or an old schema directory behind, a full pass
   replaces then
 * an attach checks after attaching that the interface still has the
   index of its pin, one recreated under the same name in between is
   reported as gone
 * a map missing from a pinned set is reported by name

v4, thanks @Stefan!:
 * drop the generation counter, a change takes the apply lock before it
   reads its input instead, so the lock order is the input order
 * new, the links of different subsystems on an interface are now
   ordered
 * the tc link plumbing is its own commit ahead of the subsystem code
 * subsystem programs are now a list of direction and name pairs
 * add short note for why not proxmox-sys's locking
 * improve tc error handling
 * fix smaller spacing and code stuff


proxmox:

Hannes Laimer (5):
  ebpf: init crate for the code shared by subsystems
  ebpf: tc: add the link plumbing
  ebpf: subsystem: add the shared tc program handling
  ebpf: subsystem: place subsystem links in a fixed order
  ebpf: debian: package the crate as a Rust library

 Cargo.toml                        |    3 +
 proxmox-ebpf/Cargo.toml           |   22 +
 proxmox-ebpf/debian/changelog     |    5 +
 proxmox-ebpf/debian/control       |   50 ++
 proxmox-ebpf/debian/copyright     |   18 +
 proxmox-ebpf/debian/debcargo.toml |    7 +
 proxmox-ebpf/src/lib.rs           |    7 +
 proxmox-ebpf/src/subsystem.rs     | 1280 +++++++++++++++++++++++++++++
 proxmox-ebpf/src/tc.rs            |  366 +++++++++
 9 files changed, 1758 insertions(+)
 create mode 100644 proxmox-ebpf/Cargo.toml
 create mode 100644 proxmox-ebpf/debian/changelog
 create mode 100644 proxmox-ebpf/debian/control
 create mode 100644 proxmox-ebpf/debian/copyright
 create mode 100644 proxmox-ebpf/debian/debcargo.toml
 create mode 100644 proxmox-ebpf/src/lib.rs
 create mode 100644 proxmox-ebpf/src/subsystem.rs
 create mode 100644 proxmox-ebpf/src/tc.rs


Summary over all repositories:
  9 files changed, 1758 insertions(+), 0 deletions(-)

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