diff --git a/Cargo.lock b/Cargo.lock
index c380aa737..4188a8166 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -199,8 +199,11 @@ dependencies = [
  "aster-time",
  "aster-util",
  "aster-virtio",
+ "atomic",
  "bitflags 1.3.2",
  "bitvec",
+ "bytemuck",
+ "bytemuck_derive",
  "controlled",
  "core2",
  "cpio-decoder",
@@ -308,6 +311,15 @@ dependencies = [
  "x86_64",
 ]
 
+[[package]]
+name = "atomic"
+version = "0.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8d818003e740b63afc82337e3160717f4f63078720a810b7b903e70a5d1d2994"
+dependencies = [
+ "bytemuck",
+]
+
 [[package]]
 name = "atomic-polyfill"
 version = "0.1.11"
@@ -364,9 +376,9 @@ dependencies = [
 
 [[package]]
 name = "bytemuck"
-version = "1.14.0"
+version = "1.14.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "374d28ec25809ee0e23827c2ab573d729e293f281dfe393500e7ad618baa61c6"
+checksum = "a2ef034f05691a48569bd920a96c81b9d91bbad1ab5ac7c4616c1f6ef36cb79f"
 dependencies = [
  "bytemuck_derive",
 ]
diff --git a/kernel/aster-nix/Cargo.toml b/kernel/aster-nix/Cargo.toml
index 3f2ada40f..45f88f69b 100644
--- a/kernel/aster-nix/Cargo.toml
+++ b/kernel/aster-nix/Cargo.toml
@@ -65,6 +65,9 @@ bitvec = { version = "1.0", default-features = false, features = ["alloc"] }
 static_assertions = "1.1.0"
 inherit-methods-macro = { git = "https://github.com/asterinas/inherit-methods-macro", rev = "98f7e3e" }
 getset = "0.1.2"
+atomic = "0.6"
+bytemuck = "1.14.3"
+bytemuck_derive = "1.5.0"
 
 [dependencies.lazy_static]
 version = "1.0"
diff --git a/kernel/aster-nix/src/fs/procfs/mod.rs b/kernel/aster-nix/src/fs/procfs/mod.rs
index 2c0833a17..ebf390494 100644
--- a/kernel/aster-nix/src/fs/procfs/mod.rs
+++ b/kernel/aster-nix/src/fs/procfs/mod.rs
@@ -112,8 +112,7 @@ impl DirOps for RootDirOps {
         let mut cached_children = this.cached_children().write();
         cached_children.put_entry_if_not_found("self", || SelfSymOps::new_inode(this_ptr.clone()));
 
-        let processes = process_table::get_all_processes();
-        for process in processes {
+        for process in process_table::process_table().iter() {
             let pid = process.pid().to_string();
             cached_children.put_entry_if_not_found(&pid, || {
                 PidDirOps::new_inode(process.clone(), this_ptr.clone())
diff --git a/kernel/aster-nix/src/process/clone.rs b/kernel/aster-nix/src/process/clone.rs
index 7f2ab8bc5..a9108c177 100644
--- a/kernel/aster-nix/src/process/clone.rs
+++ b/kernel/aster-nix/src/process/clone.rs
@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: MPL-2.0
 
+use core::sync::atomic::Ordering;
+
 use aster_frame::{cpu::UserContext, user::UserSpace, vm::VmIo};
 use aster_rights::Full;
 
@@ -260,6 +262,9 @@ fn clone_child_process(parent_context: UserContext, clone_args: CloneArgs) -> Re
         *sigmask
     };
 
+    // inherit parent's nice value
+    let child_nice = current.nice().load(Ordering::Relaxed);
+
     let child_tid = allocate_tid();
 
     let child = {
@@ -286,7 +291,8 @@ fn clone_child_process(parent_context: UserContext, clone_args: CloneArgs) -> Re
             .file_table(child_file_table)
             .fs(child_fs)
             .umask(child_umask)
-            .sig_dispositions(child_sig_dispositions);
+            .sig_dispositions(child_sig_dispositions)
+            .nice(child_nice);
 
         process_builder.build()?
     };
diff --git a/kernel/aster-nix/src/process/kill.rs b/kernel/aster-nix/src/process/kill.rs
index 6b7372397..2222a9aa9 100644
--- a/kernel/aster-nix/src/process/kill.rs
+++ b/kernel/aster-nix/src/process/kill.rs
@@ -89,13 +89,12 @@ pub fn tgkill(tid: Tid, tgid: Pid, signal: Option<UserSignal>) -> Result<()> {
 /// if it is authorized to send the signal to the target group.
 pub fn kill_all(signal: Option<UserSignal>) -> Result<()> {
     let current = current!();
-    let processes = process_table::get_all_processes();
-    for process in processes {
-        if Arc::ptr_eq(&current, &process) || process.is_init_process() {
+    for process in process_table::process_table().iter() {
+        if Arc::ptr_eq(&current, process) || process.is_init_process() {
             continue;
         }
 
-        kill_process(&process, signal)?;
+        kill_process(process, signal)?;
     }
 
     Ok(())
diff --git a/kernel/aster-nix/src/process/posix_thread/mod.rs b/kernel/aster-nix/src/process/posix_thread/mod.rs
index ccdfc01c2..1cf9a0225 100644
--- a/kernel/aster-nix/src/process/posix_thread/mod.rs
+++ b/kernel/aster-nix/src/process/posix_thread/mod.rs
@@ -246,7 +246,7 @@ impl PosixThread {
     }
 
     /// Gets the read-only credentials of the thread.
-    pub(in crate::process) fn credentials(&self) -> Credentials<ReadOp> {
+    pub fn credentials(&self) -> Credentials<ReadOp> {
         self.credentials.dup().restrict()
     }
 
diff --git a/kernel/aster-nix/src/process/process/builder.rs b/kernel/aster-nix/src/process/process/builder.rs
index b1fce90ba..3408e7e34 100644
--- a/kernel/aster-nix/src/process/process/builder.rs
+++ b/kernel/aster-nix/src/process/process/builder.rs
@@ -11,6 +11,7 @@ use crate::{
         signal::sig_disposition::SigDispositions,
         Credentials,
     },
+    sched::nice::Nice,
     thread::Thread,
 };
 
@@ -31,6 +32,7 @@ pub struct ProcessBuilder<'a> {
     resource_limits: Option<ResourceLimits>,
     sig_dispositions: Option<Arc<Mutex<SigDispositions>>>,
     credentials: Option<Credentials>,
+    nice: Option<Nice>,
 }
 
 impl<'a> ProcessBuilder<'a> {
@@ -49,6 +51,7 @@ impl<'a> ProcessBuilder<'a> {
             resource_limits: None,
             sig_dispositions: None,
             credentials: None,
+            nice: None,
         }
     }
 
@@ -102,6 +105,11 @@ impl<'a> ProcessBuilder<'a> {
         self
     }
 
+    pub fn nice(&mut self, nice: Nice) -> &mut Self {
+        self.nice = Some(nice);
+        self
+    }
+
     fn check_build(&self) -> Result<()> {
         if self.main_thread_builder.is_some() {
             debug_assert!(self.parent.upgrade().is_some());
@@ -136,6 +144,7 @@ impl<'a> ProcessBuilder<'a> {
             resource_limits,
             sig_dispositions,
             credentials,
+            nice,
         } = self;
 
         let process_vm = process_vm.or_else(|| Some(ProcessVm::alloc())).unwrap();
@@ -160,6 +169,8 @@ impl<'a> ProcessBuilder<'a> {
             .or_else(|| Some(Arc::new(Mutex::new(SigDispositions::new()))))
             .unwrap();
 
+        let nice = nice.or_else(|| Some(Nice::default())).unwrap();
+
         let process = {
             let threads = Vec::new();
             Arc::new(Process::new(
@@ -173,6 +184,7 @@ impl<'a> ProcessBuilder<'a> {
                 umask,
                 sig_dispositions,
                 resource_limits,
+                nice,
             ))
         };
 
diff --git a/kernel/aster-nix/src/process/process/mod.rs b/kernel/aster-nix/src/process/process/mod.rs
index d16c22386..7792c97f9 100644
--- a/kernel/aster-nix/src/process/process/mod.rs
+++ b/kernel/aster-nix/src/process/process/mod.rs
@@ -16,6 +16,7 @@ use crate::{
     device::tty::open_ntty_as_controlling_terminal,
     fs::{file_table::FileTable, fs_resolver::FsResolver, utils::FileCreationMask},
     prelude::*,
+    sched::nice::Nice,
     thread::{allocate_tid, Thread},
     vm::vmar::Vmar,
 };
@@ -27,6 +28,7 @@ mod session;
 mod terminal;
 
 use aster_rights::Full;
+use atomic::Atomic;
 pub use builder::ProcessBuilder;
 pub use job_control::JobControl;
 pub use process_group::ProcessGroup;
@@ -72,6 +74,10 @@ pub struct Process {
     umask: Arc<RwLock<FileCreationMask>>,
     /// resource limits
     resource_limits: Mutex<ResourceLimits>,
+    /// Scheduling priority nice value
+    /// According to POSIX.1, the nice value is a per-process attribute,
+    /// the threads in a process should share a nice value.
+    nice: Atomic<Nice>,
 
     // Signal
     /// Sig dispositions
@@ -91,6 +97,7 @@ impl Process {
         umask: Arc<RwLock<FileCreationMask>>,
         sig_dispositions: Arc<Mutex<SigDispositions>>,
         resource_limits: ResourceLimits,
+        nice: Nice,
     ) -> Self {
         let children_pauser = {
             // SIGCHID does not interrupt pauser. Child process will
@@ -114,6 +121,7 @@ impl Process {
             umask,
             sig_dispositions,
             resource_limits: Mutex::new(resource_limits),
+            nice: Atomic::new(nice),
         }
     }
 
@@ -206,7 +214,11 @@ impl Process {
         &self.resource_limits
     }
 
-    fn main_thread(&self) -> Option<Arc<Thread>> {
+    pub fn nice(&self) -> &Atomic<Nice> {
+        &self.nice
+    }
+
+    pub fn main_thread(&self) -> Option<Arc<Thread>> {
         self.threads
             .lock()
             .iter()
@@ -602,6 +614,7 @@ mod test {
             Arc::new(RwLock::new(FileCreationMask::default())),
             Arc::new(Mutex::new(SigDispositions::default())),
             ResourceLimits::default(),
+            Nice::default(),
         ))
     }
 
diff --git a/kernel/aster-nix/src/process/process/process_group.rs b/kernel/aster-nix/src/process/process/process_group.rs
index b0d7e056c..eeaa7bdd8 100644
--- a/kernel/aster-nix/src/process/process/process_group.rs
+++ b/kernel/aster-nix/src/process/process/process_group.rs
@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: MPL-2.0
 
+use alloc::collections::btree_map::Values;
+
 use super::{Pgid, Pid, Process, Session};
 use crate::{prelude::*, process::signal::signals::Signal};
 
@@ -68,6 +70,13 @@ impl ProcessGroup {
         self.pgid
     }
 
+    /// Acquires a lock on the process group.
+    pub fn lock(&self) -> ProcessGroupGuard {
+        ProcessGroupGuard {
+            inner: self.inner.lock(),
+        }
+    }
+
     /// Broadcasts signal to all processes in the group.
     ///
     /// This method should only be used to broadcast fault signal and kernel signal.
@@ -89,3 +98,32 @@ impl ProcessGroup {
         self.inner.lock().session.upgrade()
     }
 }
+
+/// A scoped lock for a process group.
+///
+/// It provides some public methods to prevent the exposure of the inner type.
+pub struct ProcessGroupGuard<'a> {
+    inner: MutexGuard<'a, Inner>,
+}
+
+impl<'a> ProcessGroupGuard<'a> {
+    /// Returns an iterator over the processes in the group.
+    pub fn iter(&self) -> ProcessGroupIter {
+        ProcessGroupIter {
+            inner: self.inner.processes.values(),
+        }
+    }
+}
+
+/// An iterator over the processes of the process group.
+pub struct ProcessGroupIter<'a> {
+    inner: Values<'a, Pid, Arc<Process>>,
+}
+
+impl<'a> Iterator for ProcessGroupIter<'a> {
+    type Item = &'a Arc<Process>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner.next()
+    }
+}
diff --git a/kernel/aster-nix/src/process/process_table.rs b/kernel/aster-nix/src/process/process_table.rs
index 499e8b3c3..a1c5c1656 100644
--- a/kernel/aster-nix/src/process/process_table.rs
+++ b/kernel/aster-nix/src/process/process_table.rs
@@ -4,6 +4,8 @@
 //! This table can be used to get process with pid.
 //! TODO: progress group, thread all need similar mapping
 
+use alloc::collections::btree_map::Values;
+
 use super::{Pgid, Pid, Process, ProcessGroup, Session, Sid};
 use crate::{
     events::{Events, Observer, Subject},
@@ -26,13 +28,40 @@ pub(super) fn process_table_mut() -> MutexGuard<'static, BTreeMap<Pid, Arc<Proce
     PROCESS_TABLE.lock()
 }
 
-/// Gets all processes
-pub fn get_all_processes() -> Vec<Arc<Process>> {
-    PROCESS_TABLE
-        .lock()
-        .iter()
-        .map(|(_, process)| process.clone())
-        .collect()
+/// Acquires a lock on the process table and returns a `ProcessTable`.
+pub fn process_table() -> ProcessTable<'static> {
+    ProcessTable {
+        inner: PROCESS_TABLE.lock(),
+    }
+}
+
+/// A wrapper for the mutex-protected process table.
+///
+/// It provides the `iter` method to iterator over the processes in the table.
+pub struct ProcessTable<'a> {
+    inner: MutexGuard<'a, BTreeMap<Pid, Arc<Process>>>,
+}
+
+impl<'a> ProcessTable<'a> {
+    /// Returns an iterator over the processes in the table.
+    pub fn iter(&self) -> ProcessTableIter {
+        ProcessTableIter {
+            inner: self.inner.values(),
+        }
+    }
+}
+
+/// An iterator over the processes of the process table.
+pub struct ProcessTableIter<'a> {
+    inner: Values<'a, Pid, Arc<Process>>,
+}
+
+impl<'a> Iterator for ProcessTableIter<'a> {
+    type Item = &'a Arc<Process>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner.next()
+    }
 }
 
 // ************ Process Group *************
diff --git a/kernel/aster-nix/src/sched/mod.rs b/kernel/aster-nix/src/sched/mod.rs
index bfa1437c3..60593247b 100644
--- a/kernel/aster-nix/src/sched/mod.rs
+++ b/kernel/aster-nix/src/sched/mod.rs
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: MPL-2.0
 
+pub mod nice;
 mod priority_scheduler;
 
 // There may be multiple scheduling policies in the system,
diff --git a/kernel/aster-nix/src/sched/nice.rs b/kernel/aster-nix/src/sched/nice.rs
new file mode 100644
index 000000000..837e42120
--- /dev/null
+++ b/kernel/aster-nix/src/sched/nice.rs
@@ -0,0 +1,111 @@
+// SPDX-License-Identifier: MPL-2.0
+
+use bytemuck_derive::NoUninit;
+
+use crate::prelude::*;
+
+/// The process scheduling nice value.
+///
+/// The nice value is an attribute that can be used to influence the
+/// CPU scheduler to favor or disfavor a process in scheduling decisions.
+///
+/// It is a value in the range -20 to 19, with -20 being the highest priority
+/// and 19 being the lowest priority. The smaller values give a process a higher
+/// scheduling priority.
+#[repr(transparent)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, NoUninit)]
+pub struct Nice {
+    value: i8,
+}
+
+impl Nice {
+    /// The minimum nice, whose value is -20.
+    pub const MIN: Self = Self { value: -20 };
+
+    /// The maximum nice, whose value is 19.
+    pub const MAX: Self = Self { value: 19 };
+
+    /// Creates a new `Nice` from the raw value.
+    ///
+    /// Values given beyond the permissible range are automatically adjusted
+    /// to the nearest boundary value.
+    pub fn new(raw: i8) -> Self {
+        if raw > Self::MAX.to_raw() {
+            Self::MAX
+        } else if raw < Self::MIN.to_raw() {
+            Self::MIN
+        } else {
+            Self { value: raw }
+        }
+    }
+
+    /// Converts to the raw value.
+    pub fn to_raw(self) -> i8 {
+        self.value
+    }
+}
+
+#[allow(clippy::derivable_impls)]
+impl Default for Nice {
+    fn default() -> Self {
+        Self {
+            // The default nice value is 0
+            value: 0,
+        }
+    }
+}
+
+impl From<Priority> for Nice {
+    fn from(priority: Priority) -> Self {
+        Self {
+            value: 20 - priority.to_raw() as i8,
+        }
+    }
+}
+
+/// The process scheduling priority value.
+///
+/// It is a value in the range 1 (corresponding to a nice value of 19)
+/// to 40 (corresponding to a nice value of -20), with 1 being the lowest priority
+/// and 40 being the highest priority. The greater values give a process a higher
+/// scheduling priority.
+#[repr(transparent)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, NoUninit)]
+pub struct Priority {
+    value: u8,
+}
+
+impl Priority {
+    /// The minimum priority, whose value is 1.
+    pub const MIN: Self = Self { value: 1 };
+
+    /// The maximum priority, whose value is 40.
+    pub const MAX: Self = Self { value: 40 };
+
+    /// Creates a new `Priority` from the raw value.
+    ///
+    /// Values given beyond the permissible range are automatically adjusted
+    /// to the nearest boundary value.
+    pub fn new(raw: u8) -> Self {
+        if raw > Self::MAX.to_raw() {
+            Self::MAX
+        } else if raw < Self::MIN.to_raw() {
+            Self::MIN
+        } else {
+            Self { value: raw }
+        }
+    }
+
+    /// Converts to the raw value.
+    pub fn to_raw(self) -> u8 {
+        self.value
+    }
+}
+
+impl From<Nice> for Priority {
+    fn from(nice: Nice) -> Self {
+        Self {
+            value: (20 - nice.to_raw()) as u8,
+        }
+    }
+}
diff --git a/kernel/aster-nix/src/syscall/mod.rs b/kernel/aster-nix/src/syscall/mod.rs
index af227248d..16052d7e0 100644
--- a/kernel/aster-nix/src/syscall/mod.rs
+++ b/kernel/aster-nix/src/syscall/mod.rs
@@ -72,6 +72,7 @@ use crate::{
         rt_sigreturn::sys_rt_sigreturn,
         sched_yield::sys_sched_yield,
         select::sys_select,
+        set_get_priority::{sys_get_priority, sys_set_priority},
         set_robust_list::sys_set_robust_list,
         set_tid_address::sys_set_tid_address,
         setpgid::sys_setpgid,
@@ -163,6 +164,7 @@ mod rt_sigreturn;
 mod sched_yield;
 mod select;
 mod sendto;
+mod set_get_priority;
 mod set_robust_list;
 mod set_tid_address;
 mod setfsgid;
@@ -321,6 +323,8 @@ define_syscall_nums!(
     SYS_SIGALTSTACK = 131,
     SYS_STATFS = 137,
     SYS_FSTATFS = 138,
+    SYS_GET_PRIORITY = 140,
+    SYS_SET_PRIORITY = 141,
     SYS_PRCTL = 157,
     SYS_ARCH_PRCTL = 158,
     SYS_SYNC = 162,
@@ -505,6 +509,8 @@ pub fn syscall_dispatch(
         SYS_SIGALTSTACK => syscall_handler!(2, sys_sigaltstack, args),
         SYS_STATFS => syscall_handler!(2, sys_statfs, args),
         SYS_FSTATFS => syscall_handler!(2, sys_fstatfs, args),
+        SYS_GET_PRIORITY => syscall_handler!(2, sys_get_priority, args),
+        SYS_SET_PRIORITY => syscall_handler!(3, sys_set_priority, args),
         SYS_PRCTL => syscall_handler!(5, sys_prctl, args),
         SYS_ARCH_PRCTL => syscall_handler!(2, sys_arch_prctl, args, context),
         SYS_SYNC => syscall_handler!(0, sys_sync),
diff --git a/kernel/aster-nix/src/syscall/set_get_priority.rs b/kernel/aster-nix/src/syscall/set_get_priority.rs
new file mode 100644
index 000000000..c849c5c16
--- /dev/null
+++ b/kernel/aster-nix/src/syscall/set_get_priority.rs
@@ -0,0 +1,149 @@
+// SPDX-License-Identifier: MPL-2.0
+
+use core::sync::atomic::Ordering;
+
+use super::{SyscallReturn, SYS_GET_PRIORITY, SYS_SET_PRIORITY};
+use crate::{
+    log_syscall_entry,
+    prelude::*,
+    process::{credentials, posix_thread::PosixThreadExt, process_table, Pgid, Pid, Process, Uid},
+    sched::nice::Nice,
+};
+
+pub fn sys_set_priority(which: i32, who: u32, prio: i32) -> Result<SyscallReturn> {
+    log_syscall_entry!(SYS_SET_PRIORITY);
+    let prio_target = PriorityTarget::new(which, who)?;
+    let new_nice = {
+        let norm_prio = if prio > i8::MAX as i32 {
+            i8::MAX
+        } else if prio < i8::MIN as i32 {
+            i8::MIN
+        } else {
+            prio as i8
+        };
+        Nice::new(norm_prio)
+    };
+
+    debug!(
+        "set_priority prio_target: {:?}, new_nice: {:?}",
+        prio_target, new_nice
+    );
+
+    let processes = get_processes(prio_target)?;
+    for process in processes.iter() {
+        process.nice().store(new_nice, Ordering::Relaxed);
+    }
+
+    Ok(SyscallReturn::Return(0))
+}
+
+pub fn sys_get_priority(which: i32, who: u32) -> Result<SyscallReturn> {
+    log_syscall_entry!(SYS_GET_PRIORITY);
+    let prio_target = PriorityTarget::new(which, who)?;
+    debug!("get_priority prio_target: {:?}", prio_target);
+
+    let processes = get_processes(prio_target)?;
+    let highest_prio = {
+        let mut nice = Nice::MAX;
+        for process in processes.iter() {
+            let proc_nice = process.nice().load(Ordering::Relaxed);
+            // Returns the highest priority enjoyed by the processes
+            if proc_nice < nice {
+                nice = proc_nice;
+            }
+        }
+
+        // The system call returns nice values translated to the range 40 to 1,
+        // since a negative return value would be interpreted as an error.
+        20 - nice.to_raw()
+    };
+
+    Ok(SyscallReturn::Return(highest_prio as _))
+}
+
+fn get_processes(prio_target: PriorityTarget) -> Result<Vec<Arc<Process>>> {
+    Ok(match prio_target {
+        PriorityTarget::Process(pid) => {
+            let process = process_table::get_process(&pid).ok_or(Error::new(Errno::ESRCH))?;
+            vec![process]
+        }
+        PriorityTarget::ProcessGroup(pgid) => {
+            let process_group =
+                process_table::get_process_group(&pgid).ok_or(Error::new(Errno::ESRCH))?;
+            let processes: Vec<Arc<Process>> = process_group.lock().iter().cloned().collect();
+            if processes.is_empty() {
+                return_errno!(Errno::ESRCH);
+            }
+            processes
+        }
+        PriorityTarget::User(uid) => {
+            // Get the processes that are running under the specified user
+            let processes: Vec<Arc<Process>> = process_table::process_table()
+                .iter()
+                .filter(|process| {
+                    let Some(main_thread) = process.main_thread() else {
+                        return false;
+                    };
+                    let Some(posix_thread) = main_thread.as_posix_thread() else {
+                        return false;
+                    };
+                    uid == posix_thread.credentials().ruid()
+                })
+                .cloned()
+                .collect();
+            if processes.is_empty() {
+                return_errno!(Errno::ESRCH);
+            }
+            processes
+        }
+    })
+}
+
+#[derive(Debug)]
+enum PriorityTarget {
+    Process(Pid),
+    ProcessGroup(Pgid),
+    User(Uid),
+}
+
+impl PriorityTarget {
+    fn new(which: i32, who: u32) -> Result<Self> {
+        let which = Which::try_from(which)
+            .map_err(|_| Error::with_message(Errno::EINVAL, "invalid which value"))?;
+        Ok(match which {
+            Which::PRIO_PROCESS => {
+                let pid = if who == 0 {
+                    current!().pid()
+                } else {
+                    who as Pid
+                };
+                Self::Process(pid)
+            }
+            Which::PRIO_PGRP => {
+                let pgid = if who == 0 {
+                    current!().pgid()
+                } else {
+                    who as Pgid
+                };
+                Self::ProcessGroup(pgid)
+            }
+            Which::PRIO_USER => {
+                let uid = if who == 0 {
+                    credentials().ruid()
+                } else {
+                    Uid::new(who)
+                };
+                Self::User(uid)
+            }
+        })
+    }
+}
+
+#[allow(non_camel_case_types)]
+#[derive(Clone, Debug, TryFromInt)]
+#[repr(i32)]
+enum Which {
+    PRIO_PROCESS = 0,
+    PRIO_PGRP = 1,
+    PRIO_USER = 2,
+}