Source code
Revision control
Copy as Markdown
Other Tools
#![cfg(target_os = "android")]
//! Provides a wrapper around Android's ASharedMemory API.
//!
//! ashmem has existed in Android as a non-public API for some time.
//! Originally accessed via ioctl, it was later available via libcutils as ashmem_create_region etc.
//! ASharedMemory is the new public API, but it isn't available until API 26 (Android 8).
//! Builds targeting Android 10 (API 29) are no longer permitted to access ashmem via the ioctl interface.
//! This makes life for a portable program difficult - you can't reliably use the old or new interface during this transition period.
//! We try to dynamically load the new API first, then fall back to the ioctl interface.
//!
//! References:
//! - [Linux ashmem.h definitions](https://elixir.bootlin.com/linux/v5.11.8/source/drivers/staging/android/uapi/ashmem.h)
#[macro_use]
extern crate ioctl_sys;
const __ASHMEMIOC: u32 = 0x77;
static mut LIBANDROID_ASHAREDMEMORY_CREATE: Option<
extern "C" fn(*const libc::c_char, libc::size_t) -> libc::c_int,
> = None;
static mut LIBANDROID_ASHAREDMEMORY_GETSIZE: Option<extern "C" fn(libc::c_int) -> libc::size_t> =
None;
static mut LIBANDROID_ASHAREDMEMORY_SETPROT: Option<
extern "C" fn(libc::c_int, libc::c_int) -> libc::c_int,
> = None;
unsafe fn maybe_init() {
const LIBANDROID_NAME: *const libc::c_char = "libandroid.so\0".as_ptr() as *const libc::c_char;
const LIBANDROID_ASHAREDMEMORY_CREATE_NAME: *const libc::c_char =
"ASharedMemory_create\0".as_ptr() as _;
const LIBANDROID_ASHAREDMEMORY_GETSIZE_NAME: *const libc::c_char =
"ASharedMemory_getSize\0".as_ptr() as _;
const LIBANDROID_ASHAREDMEMORY_SETPROT_NAME: *const libc::c_char =
"ASharedMemory_setProt\0".as_ptr() as _;
static ONCE: std::sync::Once = std::sync::Once::new();
ONCE.call_once(|| {
// Leak the handle, there's no safe time to close it.
let handle = libc::dlopen(LIBANDROID_NAME, libc::RTLD_LAZY | libc::RTLD_LOCAL);
if handle.is_null() {
return;
}
LIBANDROID_ASHAREDMEMORY_CREATE =
std::mem::transmute(libc::dlsym(handle, LIBANDROID_ASHAREDMEMORY_CREATE_NAME));
LIBANDROID_ASHAREDMEMORY_GETSIZE =
std::mem::transmute(libc::dlsym(handle, LIBANDROID_ASHAREDMEMORY_GETSIZE_NAME));
LIBANDROID_ASHAREDMEMORY_SETPROT =
std::mem::transmute(libc::dlsym(handle, LIBANDROID_ASHAREDMEMORY_SETPROT_NAME));
});
}
/// See [ASharedMemory_create NDK documentation](https://developer.android.com/ndk/reference/group/memory#asharedmemory_create)
///
/// # Safety
///
/// Directly calls C or kernel APIs.
#[allow(non_snake_case)]
pub unsafe fn ASharedMemory_create(name: *const libc::c_char, size: libc::size_t) -> libc::c_int {
const ASHMEM_NAME_DEF: *const libc::c_char = "/dev/ashmem\0".as_ptr() as _;
const ASHMEM_NAME_LEN: usize = 256;
const ASHMEM_SET_NAME: libc::c_int = iow!(
__ASHMEMIOC,
1,
std::mem::size_of::<[libc::c_char; ASHMEM_NAME_LEN]>()
) as _;
const ASHMEM_SET_SIZE: libc::c_int =
iow!(__ASHMEMIOC, 3, std::mem::size_of::<libc::size_t>()) as _;
maybe_init();
if let Some(fun) = LIBANDROID_ASHAREDMEMORY_CREATE {
return fun(name, size);
}
let fd = libc::open(ASHMEM_NAME_DEF, libc::O_RDWR, 0o600);
if fd < 0 {
return fd;
}
if !name.is_null() {
// NOTE: libcutils uses a local stack copy of `name`.
let r = libc::ioctl(fd, ASHMEM_SET_NAME, name);
if r != 0 {
libc::close(fd);
return -1;
}
}
let r = libc::ioctl(fd, ASHMEM_SET_SIZE, size);
if r != 0 {
libc::close(fd);
return -1;
}
fd
}
/// See [ASharedMemory_getSize NDK documentation](https://developer.android.com/ndk/reference/group/memory#asharedmemory_getsize)
///
/// # Safety
///
/// Directly calls C or kernel APIs.
#[allow(non_snake_case)]
pub unsafe fn ASharedMemory_getSize(fd: libc::c_int) -> libc::size_t {
const ASHMEM_GET_SIZE: libc::c_int = io!(__ASHMEMIOC, 4) as _;
maybe_init();
if let Some(fun) = LIBANDROID_ASHAREDMEMORY_GETSIZE {
return fun(fd);
}
libc::ioctl(fd, ASHMEM_GET_SIZE) as libc::size_t
}
/// See [ASharedMemory_setProt NDK documentation](https://developer.android.com/ndk/reference/group/memory#asharedmemory_setprot)
///
/// # Safety
///
/// Directly calls C or kernel APIs.
#[allow(non_snake_case)]
pub unsafe fn ASharedMemory_setProt(fd: libc::c_int, prot: libc::c_int) -> libc::c_int {
const ASHMEM_SET_PROT_MASK: libc::c_int =
iow!(__ASHMEMIOC, 5, std::mem::size_of::<libc::c_ulong>()) as _;
maybe_init();
if let Some(fun) = LIBANDROID_ASHAREDMEMORY_SETPROT {
return fun(fd, prot);
}
let r = libc::ioctl(fd, ASHMEM_SET_PROT_MASK, prot);
if r != 0 {
return -1;
}
r
}
#[cfg(test)]
mod tests {
#[test]
fn basic() {
unsafe {
let name = std::ffi::CString::new("/test-ashmem").unwrap();
let fd = super::ASharedMemory_create(name.as_ptr(), 128);
assert!(fd >= 0);
assert_eq!(super::ASharedMemory_getSize(fd), 128);
assert_eq!(super::ASharedMemory_setProt(fd, 0), 0);
libc::close(fd);
}
}
#[test]
fn anonymous() {
unsafe {
let fd = super::ASharedMemory_create(std::ptr::null(), 128);
assert!(fd >= 0);
libc::close(fd);
}
}
}