aya,aya-obj: cache feat probed info fields

Cached probed for ProgramInfo fields instead of exposing it through
global FEATURE. Probing occurs on cache miss, which happens when first
accessing the field, *and* if the field is 0.

Author: tyrone-wu

aya-obj/src/obj.rs

@@ -46,8 +46,6 @@ pub struct Features {
     bpf_cookie: bool,
     cpumap_prog_id: bool,
     devmap_prog_id: bool,
-    prog_info_map_ids: bool,
-    prog_info_gpl_compatible: bool,
     btf: Option<BtfFeatures>,
 }
 
@@ -62,8 +60,6 @@ impl Features {
         bpf_cookie: bool,
         cpumap_prog_id: bool,
         devmap_prog_id: bool,
-        prog_info_map_ids: bool,
-        prog_info_gpl_compatible: bool,
         btf: Option<BtfFeatures>,
     ) -> Self {
         Self {
@@ -74,8 +70,6 @@ impl Features {
             bpf_cookie,
             cpumap_prog_id,
             devmap_prog_id,
-            prog_info_map_ids,
-            prog_info_gpl_compatible,
             btf,
         }
     }
@@ -118,16 +112,6 @@ impl Features {
         self.devmap_prog_id
     }
 
-    /// Returns whether `bpf_prog_info` supports `nr_map_ids` & `map_ids` fields.
-    pub fn prog_info_map_ids(&self) -> bool {
-        self.prog_info_map_ids
-    }
-
-    /// Returns whether `bpf_prog_info` supports `gpl_compatible` field.
-    pub fn prog_info_gpl_compatible(&self) -> bool {
-        self.prog_info_gpl_compatible
-    }
-
     /// If BTF is supported, returns which BTF features are supported.
     pub fn btf(&self) -> Option<&BtfFeatures> {
         self.btf.as_ref()

aya/Cargo.toml

@@ -22,7 +22,7 @@ hashbrown = { workspace = true }
 libc = { workspace = true }
 log = { workspace = true }
 object = { workspace = true, features = ["elf", "read_core", "std", "write"] }
-once_cell = { workspace = true }
+once_cell = { workspace = true, features = ["race"] }
 thiserror = { workspace = true }
 tokio = { workspace = true, features = ["rt"], optional = true }
 

aya/src/bpf.rs

@@ -31,9 +31,9 @@ use crate::{
         bpf_load_btf, is_bpf_cookie_supported, is_bpf_global_data_supported,
         is_btf_datasec_supported, is_btf_decl_tag_supported, is_btf_enum64_supported,
         is_btf_float_supported, is_btf_func_global_supported, is_btf_func_supported,
-        is_btf_supported, is_btf_type_tag_supported, is_info_gpl_compatible_supported,
-        is_info_map_ids_supported, is_perf_link_supported, is_probe_read_kernel_supported,
-        is_prog_id_supported, is_prog_name_supported, retry_with_verifier_logs,
+        is_btf_supported, is_btf_type_tag_supported, is_perf_link_supported,
+        is_probe_read_kernel_supported, is_prog_id_supported, is_prog_name_supported,
+        retry_with_verifier_logs,
     },
     util::{bytes_of, bytes_of_slice, nr_cpus, page_size},
 };
@@ -80,8 +80,6 @@ fn detect_features() -> Features {
         is_bpf_cookie_supported(),
         is_prog_id_supported(BPF_MAP_TYPE_CPUMAP),
         is_prog_id_supported(BPF_MAP_TYPE_DEVMAP),
-        is_info_map_ids_supported(),
-        is_info_gpl_compatible_supported(),
         btf,
     );
     debug!("BPF Feature Detection: {:#?}", f);

aya/src/programs/info.rs

@@ -8,14 +8,17 @@ use std::{
 };
 
 use aya_obj::generated::{bpf_prog_info, bpf_prog_type};
+use once_cell::race::OnceBool;
 
 use super::{
     utils::{boot_time, get_fdinfo},
     ProgramError, ProgramFd,
 };
 use crate::{
     sys::{
-        bpf_get_object, bpf_prog_get_fd_by_id, bpf_prog_get_info_by_fd, iter_prog_ids, SyscallError,
+        bpf_get_object, bpf_prog_get_fd_by_id, bpf_prog_get_info_by_fd,
+        feature_probe::{is_prog_info_license_supported, is_prog_info_map_ids_supported},
+        iter_prog_ids, SyscallError,
     },
     util::bytes_of_bpf_name,
     FEATURES,
@@ -108,10 +111,15 @@ impl ProgramInfo {
     ///
     /// Introduced in kernel v4.15.
     pub fn map_ids(&self) -> Result<Option<Vec<u32>>, ProgramError> {
-        if FEATURES.prog_info_map_ids() {
+        if self.0.nr_map_ids > 0 {
             let mut map_ids = vec![0u32; self.0.nr_map_ids as usize];
             bpf_prog_get_info_by_fd(self.fd()?.as_fd(), &mut map_ids)?;
-            Ok(Some(map_ids))
+            return Ok(Some(map_ids));
+        }
+
+        static CACHE: OnceBool = OnceBool::new();
+        if CACHE.get_or_init(|| matches!(is_prog_info_map_ids_supported(), Ok(true))) {
+            Ok(Some(vec![]))
         } else {
             Ok(None)
         }
@@ -140,9 +148,16 @@ impl ProgramInfo {
     ///
     /// Introduced in kernel v4.18.
     pub fn gpl_compatible(&self) -> Option<bool> {
-        FEATURES
-            .prog_info_gpl_compatible()
-            .then_some(self.0.gpl_compatible() != 0)
+        if self.0.gpl_compatible() != 0 {
+            return Some(true);
+        }
+
+        static CACHE: OnceBool = OnceBool::new();
+        if CACHE.get_or_init(|| matches!(is_prog_info_license_supported(), Ok(true))) {
+            Some(false)
+        } else {
+            None
+        }
     }
 
     /// The BTF ID for the program.

aya/src/sys/bpf.rs

@@ -29,7 +29,7 @@ use crate::{
     programs::links::LinkRef,
     sys::{syscall, Syscall, SyscallError},
     util::KernelVersion,
-    Btf, Pod, VerifierLogLevel, FEATURES,
+    Btf, Pod, VerifierLogLevel,
 };
 
 pub(crate) fn bpf_create_iter(link_fd: BorrowedFd<'_>) -> io::Result<crate::MockableFd> {
@@ -595,7 +595,7 @@ pub(crate) fn bpf_prog_get_info_by_fd(
     // An `E2BIG` error can occur on kernels below v4.15 when handing over a large struct where the
     // extra space is not all-zero bytes.
     bpf_obj_get_info_by_fd(fd, |info: &mut bpf_prog_info| {
-        if FEATURES.prog_info_map_ids() {
+        if !map_ids.is_empty() {
             info.nr_map_ids = map_ids.len() as _;
             info.map_ids = map_ids.as_mut_ptr() as _;
         }
@@ -753,34 +753,6 @@ where
     op(&mut attr)
 }
 
-/// Tests whether `nr_map_ids` & `map_ids` fields in `bpf_prog_info` is available.
-pub(crate) fn is_info_map_ids_supported() -> bool {
-    with_trivial_prog(|attr| {
-        let prog_fd = match bpf_prog_load(attr) {
-            Ok(fd) => fd,
-            Err(_) => return false,
-        };
-        bpf_obj_get_info_by_fd(prog_fd.as_fd(), |info: &mut bpf_prog_info| {
-            info.nr_map_ids = 1
-        })
-        .is_ok()
-    })
-}
-
-/// Tests whether `gpl_compatible` field in `bpf_prog_info` is available.
-pub(crate) fn is_info_gpl_compatible_supported() -> bool {
-    with_trivial_prog(|attr| {
-        let prog_fd = match bpf_prog_load(attr) {
-            Ok(fd) => fd,
-            Err(_) => return false,
-        };
-        if let Ok::<bpf_prog_info, _>(info) = bpf_obj_get_info_by_fd(prog_fd.as_fd(), |_| {}) {
-            return info.gpl_compatible() != 0;
-        }
-        false
-    })
-}
-
 pub(crate) fn is_probe_read_kernel_supported() -> bool {
     let mut attr = unsafe { mem::zeroed::<bpf_attr>() };
     let u = unsafe { &mut attr.__bindgen_anon_3 };
@@ -1090,7 +1062,7 @@ fn sys_bpf(cmd: bpf_cmd, attr: &mut bpf_attr) -> io::Result<c_long> {
     })
 }
 
-fn unit_sys_bpf(cmd: bpf_cmd, attr: &mut bpf_attr) -> io::Result<()> {
+pub(super) fn unit_sys_bpf(cmd: bpf_cmd, attr: &mut bpf_attr) -> io::Result<()> {
     sys_bpf(cmd, attr).map(|code| assert_eq!(code, 0))
 }
 

aya/src/sys/feature_probe.rs

@@ -5,17 +5,18 @@ use std::{io::ErrorKind, mem, os::fd::AsRawFd};
 use aya_obj::{
     btf::{Btf, BtfError, BtfKind},
     generated::{
-        bpf_attach_type, bpf_attr, bpf_cmd, bpf_map_type, BPF_F_MMAPABLE, BPF_F_NO_PREALLOC,
-        BPF_F_SLEEPABLE,
+        bpf_attach_type, bpf_attr, bpf_cmd, bpf_map_type, bpf_prog_info, BPF_F_MMAPABLE,
+        BPF_F_NO_PREALLOC, BPF_F_SLEEPABLE,
     },
 };
 use libc::{E2BIG, EBADF, EINVAL};
 
-use super::{bpf_prog_load, fd_sys_bpf, with_trivial_prog, SyscallError};
+use super::{bpf_prog_load, fd_sys_bpf, unit_sys_bpf, with_trivial_prog, SyscallError};
 use crate::{
     maps::MapType,
     programs::{ProgramError, ProgramType},
     util::{page_size, KernelVersion},
+    MockableFd,
 };
 
 /// Whether the host kernel supports the [`ProgramType`].
@@ -226,6 +227,26 @@ pub fn is_map_supported(map_type: MapType) -> Result<bool, SyscallError> {
     }
 }
 
+/// Whether `nr_map_ids` & `map_ids` fields in `bpf_prog_info` are supported.
+pub(crate) fn is_prog_info_map_ids_supported() -> Result<bool, ProgramError> {
+    let fd = create_minimal_program(ProgramType::SocketFilter, &mut [])?;
+    // SAFETY: all-zero byte-pattern valid for `bpf_prog_info`
+    let mut info = unsafe { mem::zeroed::<bpf_prog_info>() };
+    info.nr_map_ids = 1;
+
+    probe_bpf_info(fd, info).map_err(ProgramError::from)
+}
+
+/// Tests whether `bpf_prog_info.gpl_compatible` field is supported.
+pub(crate) fn is_prog_info_license_supported() -> Result<bool, ProgramError> {
+    let fd = create_minimal_program(ProgramType::SocketFilter, &mut [])?;
+    // SAFETY: all-zero byte-pattern valid for `bpf_prog_info`
+    let mut info = unsafe { mem::zeroed::<bpf_prog_info>() };
+    info.set_gpl_compatible(1);
+
+    probe_bpf_info(fd, info).map_err(ProgramError::from)
+}
+
 /// Create a minimal program with the specified type.
 /// Types not created for `Extension` and `StructOps`.
 fn create_minimal_program(
@@ -281,3 +302,25 @@ fn create_minimal_program(
         })
     })
 }
+
+/// Probes program and map info.
+fn probe_bpf_info<T>(fd: MockableFd, info: T) -> Result<bool, SyscallError> {
+    // SAFETY: all-zero byte-pattern valid for `bpf_attr`
+    let mut attr = unsafe { mem::zeroed::<bpf_attr>() };
+    attr.info.bpf_fd = fd.as_raw_fd() as u32;
+    attr.info.info_len = mem::size_of_val(&info) as u32;
+    attr.info.info = &info as *const _ as u64;
+
+    let io_error = match unit_sys_bpf(bpf_cmd::BPF_OBJ_GET_INFO_BY_FD, &mut attr) {
+        Ok(()) => return Ok(true),
+        Err(io_error) => io_error,
+    };
+    match io_error.raw_os_error() {
+        // `E2BIG` from `bpf_check_uarg_tail_zero()`
+        Some(E2BIG) => Ok(false),
+        _ => Err(SyscallError {
+            call: "bpf_obj_get_info_by_fd",
+            io_error,
+        }),
+    }
+}

test/integration-test/src/tests/feature_probe.rs

@@ -7,8 +7,6 @@ use aya::{maps::MapType, programs::ProgramType, sys::feature_probe::*, util::Ker
 
 use super::load::RETRY_DURATION;
 
-use super::load::RETRY_DURATION;
-
 // TODO: Enable certain CONFIG_* options when compiling the image for VM tests.
 #[test]
 fn probe_supported_programs() {