sys::prctl: Adding set_vma_anon_name. (#2378)

to set a name for an `anonymous` region for Linux/Android.

Author: devnexen

changelog/2378.added.md

@@ -0,0 +1 @@
+Add prctl function `prctl_set_vma_anon_name` for Linux/Android.

src/sys/prctl.rs

@@ -9,9 +9,11 @@ use crate::errno::Errno;
 use crate::sys::signal::Signal;
 use crate::Result;
 
-use libc::{c_int, c_ulong};
+use libc::{c_int, c_ulong, c_void};
 use std::convert::TryFrom;
 use std::ffi::{CStr, CString};
+use std::num::NonZeroUsize;
+use std::ptr::NonNull;
 
 libc_enum! {
     /// The type of hardware memory corruption kill policy for the thread.
@@ -213,3 +215,14 @@ pub fn set_thp_disable(flag: bool) -> Result<()> {
 pub fn get_thp_disable() -> Result<bool> {
     prctl_get_bool(libc::PR_GET_THP_DISABLE)
 }
+
+/// Set an identifier (or reset it) to the address memory range.
+pub fn set_vma_anon_name(addr: NonNull<c_void>, length: NonZeroUsize, name: Option<&CStr>) -> Result<()> {
+    let nameref = match name {
+        Some(n) => n.as_ptr(),
+        _ => std::ptr::null()
+    };
+    let res = unsafe { libc::prctl(libc::PR_SET_VMA, libc::PR_SET_VMA_ANON_NAME, addr.as_ptr(), length, nameref) };
+
+    Errno::result(res).map(drop)
+}

test/sys/test_prctl.rs

@@ -122,4 +122,38 @@ mod test_prctl {
 
         prctl::set_thp_disable(original).unwrap();
     }
+
+    #[test]
+    fn test_set_vma_anon_name() {
+        use nix::errno::Errno;
+        use nix::sys::mman;
+        use std::num::NonZeroUsize;
+
+        const ONE_K: libc::size_t = 1024;
+        let sz = NonZeroUsize::new(ONE_K).unwrap();
+        let ptr = unsafe {
+            mman::mmap_anonymous(
+                None,
+                sz,
+                mman::ProtFlags::PROT_READ,
+                mman::MapFlags::MAP_SHARED,
+            )
+            .unwrap()
+        };
+        let err = prctl::set_vma_anon_name(
+            ptr,
+            sz,
+            Some(CStr::from_bytes_with_nul(b"[,$\0").unwrap()),
+        )
+        .unwrap_err();
+        assert_eq!(err, Errno::EINVAL);
+        // `CONFIG_ANON_VMA_NAME` kernel config might not be set
+        prctl::set_vma_anon_name(
+            ptr,
+            sz,
+            Some(CStr::from_bytes_with_nul(b"Nix\0").unwrap()),
+        )
+        .unwrap_or_default();
+        prctl::set_vma_anon_name(ptr, sz, None).unwrap_or_default();
+    }
 }