ANDROID: ashmem_rust: add GET/SET_NAME

Add the first ioctl to the ashmem device. The `Ashmem` struct is
augmented with a mutex to hold the name.

The Rust bindings helper is updated to pull in constants from the
existing C header. For now, only ASHMEM_NAME_LEN is needed, but later
patches will need more stuff from the C header.

Bug: 370906207
Change-Id: I7fbbce12e1fa7c4fb811fcb2561806795ba2bd0f
Signed-off-by: Alice Ryhl <aliceryhl@google.com>

drivers/staging/android/ashmem_rust.rs

@@ -12,13 +12,18 @@
 
 use core::pin::Pin;
 use kernel::{
-    c_str,
+    bindings, c_str,
     error::Result,
     fs::File,
+    ioctl::_IOC_SIZE,
     miscdevice::{MiscDevice, MiscDeviceOptions, MiscDeviceRegistration},
     prelude::*,
+    sync::{new_mutex, Mutex},
+    uaccess::{UserSlice, UserSliceReader, UserSliceWriter},
 };
 
+const ASHMEM_NAME_LEN: usize = bindings::ASHMEM_NAME_LEN as usize;
+
 module! {
     type: AshmemModule,
     name: "ashmem_rust",
@@ -48,13 +53,81 @@ impl kernel::Module for AshmemModule {
 
 /// Represents an open ashmem file.
 #[pin_data]
-struct Ashmem {}
+struct Ashmem {
+    #[pin]
+    inner: Mutex<AshmemInner>,
+}
+
+struct AshmemInner {
+    /// If set, then this holds the ashmem name without the dev/ashmem/ prefix. No zero terminator.
+    name: Option<Vec<u8>>,
+}
 
 #[vtable]
 impl MiscDevice for Ashmem {
     type Ptr = Pin<Box<Self>>;
 
     fn open(_: &File, _: &MiscDeviceRegistration<Ashmem>) -> Result<Pin<Box<Self>>> {
-        Box::try_pin_init(Ashmem {}, GFP_KERNEL)
+        Box::try_pin_init(
+            try_pin_init! {
+                Ashmem {
+                    inner <- new_mutex!(AshmemInner {
+                        name: None,
+                    }),
+                }
+            },
+            GFP_KERNEL,
+        )
+    }
+
+    fn ioctl(me: Pin<&Ashmem>, _file: &File, cmd: u32, arg: usize) -> Result<isize> {
+        let size = _IOC_SIZE(cmd);
+        match cmd {
+            bindings::ASHMEM_SET_NAME => me.set_name(UserSlice::new(arg, size).reader()),
+            bindings::ASHMEM_GET_NAME => me.get_name(UserSlice::new(arg, size).writer()),
+            _ => Err(EINVAL),
+        }
+    }
+}
+
+impl Ashmem {
+    fn set_name(&self, mut reader: UserSliceReader) -> Result<isize> {
+        let mut local_name = [0u8; ASHMEM_NAME_LEN];
+        reader.read_slice(&mut local_name)?;
+
+        // Find the zero terminator. If the zero terminator is missing, the string is truncated to
+        // `ASHMEM_NAME_LEN-1` so that `get_name` can return it and has enough space to add a zero
+        // terminator.
+        let len = local_name
+            .iter()
+            .position(|&c| c == 0)
+            .unwrap_or(local_name.len() - 1);
+
+        let mut v = Vec::with_capacity(len, GFP_KERNEL)?;
+        v.extend_from_slice(&local_name[..len], GFP_KERNEL)?;
+
+        let mut asma = self.inner.lock();
+        // TODO: fail if `mmap` is already called
+        asma.name = Some(v);
+        Ok(0)
+    }
+
+    fn get_name(&self, mut writer: UserSliceWriter) -> Result<isize> {
+        let mut local_name = [0u8; ASHMEM_NAME_LEN];
+        let asma = self.inner.lock();
+        let name = asma.name.as_deref().unwrap_or(b"dev/ashmem");
+        let len = name.len();
+        let len_with_nul = len + 1;
+        if local_name.len() <= len_with_nul {
+            // This shouldn't happen in practice since `set_name` will refuse to store a string
+            // that is too long.
+            return Err(EINVAL);
+        }
+        local_name[..len].copy_from_slice(name);
+        local_name[len_with_nul] = 0;
+        drop(asma);
+
+        writer.write_slice(&local_name[..len_with_nul])?;
+        Ok(0)
     }
 }

rust/bindings/bindings_helper.h

@@ -45,3 +45,7 @@ const gfp_t RUST_CONST_HELPER_GFP_NOWAIT = GFP_NOWAIT;
 const gfp_t RUST_CONST_HELPER___GFP_ZERO = __GFP_ZERO;
 const gfp_t RUST_CONST_HELPER___GFP_HIGHMEM = ___GFP_HIGHMEM;
 const blk_features_t RUST_CONST_HELPER_BLK_FEAT_ROTATIONAL = BLK_FEAT_ROTATIONAL;
+
+#ifdef CONFIG_ASHMEM_RUST
+#include "../../drivers/staging/android/ashmem.h"
+#endif