Implement the syscall `shmget`

kernel/src/syscall/shmget.rs

@@ -12,4 +12,72 @@ use crate::{
 };
 
 pub fn sys_shmget(key: i32, size: usize, flags: i32, ctx: &Context) -> Result<SyscallReturn> {
+    const IPC_PRIVATE: i32 = 0;
+    const INODE_MODE_MASK: i32 = 0o777;
+    if key < 0 {
+        return_errno!(Errno::EINVAL);
+    }
+    if size <= SHMMIN || size > SHMMAX {
+        return_errno!(Errno::EINVAL);
+    }
+
+    let mode = InodeMode::from_bits_truncate((flags & INODE_MODE_MASK) as u16);
+    let flags = IpcFlags::from_bits_truncate(flags as u32);
+
+    debug!(
+        "[sys_shmget] key = {}, size = {}, flags = {:?}",
+        key, size, flags
+    );
+    let uid = Uid::new_root();
+    let gid = Gid::new_root();
+    let cpid = ctx.process.pid();
+
+    let manager = SHM_OBJ_MANAGER.get().ok_or(Errno::EINVAL)?;
+
+    let shmid = if key == IPC_PRIVATE {
+        // If key is IPC_PRIVATE, create an anonymous shared memory segment
+        manager.write().create_shm_anonymous(size, mode, cpid)?
+    } else {
+        let shm_key = key as u32;
+        let shmid = manager.read().get_shmid_by_key(shm_key);
+
+        if let Some(existing_shmid) = shmid {
+            let shm_obj = manager
+                .read()
+                .get_shm_obj(existing_shmid)
+                .ok_or(Errno::ENOENT)?;
+            let mode = shm_obj.mode()?;
+
+            if size > shm_obj.size() {
+                return_errno!(Errno::EINVAL);
+            }
+
+            if u32::from(uid) == shm_obj.uid()? {
+                if !mode.contains(InodeMode::S_IRUSR) {
+                    return_errno!(Errno::EACCES);
+                }
+            } else if u32::from(gid) == shm_obj.gid()? {
+                if !mode.contains(InodeMode::S_IRGRP) {
+                    return_errno!(Errno::EACCES);
+                }
+            } else if !mode.contains(InodeMode::S_IROTH) {
+                return_errno!(Errno::EACCES);
+            }
+
+            if flags.contains(IpcFlags::IPC_CREAT) && flags.contains(IpcFlags::IPC_EXCL) {
+                // Setting both IPC_CREAT and IPC_EXCL means to create a new segment, thus fail when it already exists
+                return_errno!(Errno::EEXIST);
+            }
+
+            existing_shmid
+        } else if flags.contains(IpcFlags::IPC_CREAT) {
+            // Create a new shared memory segment
+            manager.write().create_shm(shm_key, size, mode, cpid)?
+        } else {
+            // If IPC_CREAT is not set, the segment must exist
+            return_errno!(Errno::ENOENT);
+        }
+    };
+
+    Ok(SyscallReturn::Return(shmid as _))
 }