Add `proc/self/mounts` and `proc/mounts`

kernel/src/device/mod.rs

@@ -36,7 +36,12 @@ pub fn init_in_first_process(ctx: &Context) -> Result<()> {
 
     // Mount devtmpfs.
     let dev_path = path_resolver.lookup(&FsPath::try_from("/dev")?)?;
-    dev_path.mount(RamFs::new(), PerMountFlags::default(), ctx)?;
+    dev_path.mount(
+        RamFs::new(),
+        PerMountFlags::default(),
+        Some("ramfs".to_string()),
+        ctx,
+    )?;
 
     tty::init_in_first_process()?;
     pty::init_in_first_process(&path_resolver, ctx)?;

kernel/src/device/pty/mod.rs

@@ -24,7 +24,12 @@ pub fn init_in_first_process(path_resolver: &PathResolver, ctx: &Context) -> Res
     let dev = path_resolver.lookup(&FsPath::try_from("/dev")?)?;
     // Create the "pts" directory and mount devpts on it.
     let devpts_path = dev.new_fs_child("pts", InodeType::Dir, mkmod!(a+rx, u+w))?;
-    let devpts_mount = devpts_path.mount(DevPts::new(), PerMountFlags::default(), ctx)?;
+    let devpts_mount = devpts_path.mount(
+        DevPts::new(),
+        PerMountFlags::default(),
+        Some("devpts".to_string()),
+        ctx,
+    )?;
 
     DEV_PTS.call_once(|| Path::new_fs_root(devpts_mount));
 

kernel/src/device/shm.rs

@@ -18,7 +18,12 @@ pub fn init_in_first_process(path_resolver: &PathResolver, ctx: &Context) -> Res
     // Create the "shm" directory under "/dev" and mount a ramfs on it.
     let shm_path =
         dev_path.new_fs_child("shm", InodeType::Dir, chmod!(InodeMode::S_ISVTX, a+rwx))?;
-    shm_path.mount(RamFs::new(), PerMountFlags::default(), ctx)?;
+    shm_path.mount(
+        RamFs::new(),
+        PerMountFlags::default(),
+        Some("tmpfs".to_string()),
+        ctx,
+    )?;
     log::debug!("Mount RamFs at \"/dev/shm\"");
     Ok(())
 }

kernel/src/fs/path/dentry.rs

@@ -18,7 +18,7 @@ use crate::{
 };
 
 /// A `Dentry` represents a cached filesystem node in the VFS tree.
-pub(super) struct Dentry {
+pub(in crate::fs) struct Dentry {
     inode: Arc<dyn Inode>,
     type_: InodeType,
     name_and_parent: NameAndParent,
@@ -203,7 +203,7 @@ impl Dentry {
     }
 
     /// Gets the absolute path name of this `Dentry` within the filesystem.
-    pub(super) fn path_name(&self) -> String {
+    pub(in crate::fs) fn path_name(&self) -> String {
         let mut path_name = self.name().to_string();
         let mut current_dir = self.this();
 

kernel/src/fs/path/mod.rs

@@ -78,7 +78,7 @@ impl Path {
         Self::new(mount, dentry)
     }
 
-    fn new(mount: Arc<Mount>, dentry: Arc<Dentry>) -> Self {
+    pub(in crate::fs) fn new(mount: Arc<Mount>, dentry: Arc<Dentry>) -> Self {
         Self { mount, dentry }
     }
 
@@ -87,6 +87,11 @@ impl Path {
         &self.mount
     }
 
+    /// Gets the dentry of current `Path`.
+    pub(in crate::fs) fn dentry(&self) -> &Arc<Dentry> {
+        &self.dentry
+    }
+
     /// Returns true if the current `Path` is the root of its mount.
     pub fn is_mount_root(&self) -> bool {
         Arc::ptr_eq(&self.dentry, self.mount.root_dentry())
@@ -203,6 +208,7 @@ impl Path {
         &self,
         fs: Arc<dyn FileSystem>,
         flags: PerMountFlags,
+        source: Option<String>,
         ctx: &Context,
     ) -> Result<Arc<Mount>> {
         if self.type_() != InodeType::Dir {
@@ -222,7 +228,7 @@ impl Path {
             return_errno_with_message!(Errno::EINVAL, "the path is not in this mount namespace");
         }
 
-        let child_mount = self.mount.do_mount(fs, flags, &self.dentry)?;
+        let child_mount = self.mount.do_mount(fs, flags, &self.dentry, source)?;
 
         Ok(child_mount)
     }

kernel/src/fs/path/mount.rs

@@ -160,6 +160,15 @@ pub struct Mount {
     mountpoint: RwLock<Option<Arc<Dentry>>>,
     /// The associated FS.
     fs: Arc<dyn FileSystem>,
+    /// The mount source (e.g., a device path like "/dev/vda" or a filesystem name like "proc").
+    ///
+    /// The source is stored in `Mount` instead of requiring each filesystem to provide it.
+    /// If a filesystem does not provide a source, it falls back to the value stored in `Mount`.
+    /// This behavior aligns with that of Linux. Concrete examples can be found here:
+    /// <https://github.com/asterinas/asterinas/pull/2929#discussion_r2729739818>.
+    ///
+    /// Reference: <https://elixir.bootlin.com/linux/v6.17/source/fs/mount.h#L68>
+    source: Option<String>,
     /// The parent mount node.
     parent: RwLock<Option<Weak<Mount>>>,
     /// Child mount nodes which are mounted on one dentry of self.
@@ -186,7 +195,8 @@ impl Mount {
         fs: Arc<dyn FileSystem>,
         mnt_ns: Weak<MountNamespace>,
     ) -> Arc<Self> {
-        Self::new(fs, PerMountFlags::default(), None, mnt_ns)
+        let source = fs.name().to_string();
+        Self::new(fs, PerMountFlags::default(), None, mnt_ns, Some(source))
     }
 
     /// Creates a pseudo mount node with an associated FS.
@@ -194,7 +204,7 @@ impl Mount {
     /// This pseudo mount is not mounted on other mount nodes, has no parent, and does not
     /// belong to any mount namespace.
     pub(in crate::fs) fn new_pseudo(fs: Arc<dyn FileSystem>) -> Arc<Self> {
-        Self::new(fs, PerMountFlags::KERNMOUNT, None, Weak::new())
+        Self::new(fs, PerMountFlags::KERNMOUNT, None, Weak::new(), None)
     }
 
     /// The internal constructor.
@@ -210,6 +220,7 @@ impl Mount {
         flags: PerMountFlags,
         parent_mount: Option<Weak<Mount>>,
         mnt_ns: Weak<MountNamespace>,
+        source: Option<String>,
     ) -> Arc<Self> {
         let id = ID_ALLOCATOR.get().unwrap().lock().alloc().unwrap();
 
@@ -221,6 +232,7 @@ impl Mount {
             children: RwLock::new(HashMap::new()),
             propagation: RwLock::new(MountPropType::default()),
             fs,
+            source,
             mnt_ns,
             flags: AtomicPerMountFlags::new(flags),
             this: weak_self.clone(),
@@ -232,6 +244,11 @@ impl Mount {
         self.id
     }
 
+    /// Returns the mount source.
+    pub(in crate::fs) fn source(&self) -> Option<&str> {
+        self.fs.source().or(self.source.as_deref())
+    }
+
     /// Mounts a fs on the mountpoint, it will create a new child mount node.
     ///
     /// If the given mountpoint has already been mounted, then its mounted child mount
@@ -242,19 +259,28 @@ impl Mount {
     /// It is allowed to mount a fs even if the fs has been provided to another
     /// mountpoint. It is the fs's responsibility to ensure the data consistency.
     ///
+    /// If the source is provided by user, it will be recorded in the new mount.
+    ///
     /// Return the mounted child mount.
     pub(super) fn do_mount(
         self: &Arc<Self>,
         fs: Arc<dyn FileSystem>,
         flags: PerMountFlags,
         mountpoint: &Arc<Dentry>,
+        source: Option<String>,
     ) -> Result<Arc<Self>> {
         if mountpoint.type_() != InodeType::Dir {
             return_errno!(Errno::ENOTDIR);
         }
 
         let key = mountpoint.key();
-        let child_mount = Self::new(fs, flags, Some(Arc::downgrade(self)), self.mnt_ns.clone());
+        let child_mount = Self::new(
+            fs,
+            flags,
+            Some(Arc::downgrade(self)),
+            self.mnt_ns.clone(),
+            source,
+        );
         self.children.write().insert(key, child_mount.clone());
         child_mount.set_mountpoint(mountpoint);
 
@@ -296,6 +322,7 @@ impl Mount {
             children: RwLock::new(HashMap::new()),
             propagation: RwLock::new(MountPropType::default()),
             fs: self.fs.clone(),
+            source: self.source.clone(),
             mnt_ns: new_ns.cloned().unwrap_or_else(|| self.mnt_ns.clone()),
             flags: AtomicPerMountFlags::new(self.flags.load(Ordering::Relaxed)),
             this: weak_self.clone(),
@@ -405,12 +432,12 @@ impl Mount {
     }
 
     /// Gets the root `Dentry` of this mount node.
-    pub(super) fn root_dentry(&self) -> &Arc<Dentry> {
+    pub(in crate::fs) fn root_dentry(&self) -> &Arc<Dentry> {
         &self.root_dentry
     }
 
     /// Gets the mountpoint `Dentry` of this mount node if any.
-    pub(super) fn mountpoint(&self) -> Option<Arc<Dentry>> {
+    pub(in crate::fs) fn mountpoint(&self) -> Option<Arc<Dentry>> {
         self.mountpoint.read().clone()
     }
 
@@ -481,7 +508,7 @@ impl Mount {
     }
 
     /// Gets the parent mount node if any.
-    pub(super) fn parent(&self) -> Option<Weak<Self>> {
+    pub(in crate::fs) fn parent(&self) -> Option<Weak<Self>> {
         self.parent.read().as_ref().cloned()
     }
 
@@ -491,11 +518,11 @@ impl Mount {
     }
 
     /// Gets the associated FS.
-    pub(super) fn fs(&self) -> &Arc<dyn FileSystem> {
+    pub(in crate::fs) fn fs(&self) -> &Arc<dyn FileSystem> {
         &self.fs
     }
 
-    pub(super) fn flags(&self) -> PerMountFlags {
+    pub(in crate::fs) fn flags(&self) -> PerMountFlags {
         self.flags.load(Ordering::Relaxed)
     }
 

kernel/src/fs/path/resolver.rs

@@ -2,15 +2,14 @@
 
 use alloc::str;
 
-use aster_util::printer::VmPrinter;
 use ostd::task::Task;
 
-use super::Path;
+use super::{Mount, Path};
 use crate::{
     fs::{
         file_table::{FileDesc, get_file_fast},
-        path::{MountNamespace, PerMountFlags},
+        path::MountNamespace,
-        utils::{FsFlags, InodeType, NAME_MAX, PATH_MAX, Permission, SYMLINKS_MAX, SymbolicLink},
+        utils::{InodeType, NAME_MAX, PATH_MAX, Permission, SYMLINKS_MAX, SymbolicLink},
     },
     prelude::*,
     process::posix_thread::AsThreadLocal,
@@ -253,122 +252,43 @@ impl AbsPathResult {
 
 // Mount info reading implementation
 impl PathResolver {
-    /// Reads the information of the mounts visible to this resolver.
+    /// Collects the mounts visible to this resolver.
     ///
     /// Here, the visible mounts are defined as follows:
     /// 1. If the resolver's root is a mount point, the visible mounts are the mount of the
     ///    resolver's root directory and all of its descendant mounts in the mount tree.
     /// 2. If the resolver's root is not a mount point, the visible mounts are all descendant
     ///    mounts that are mounted under the resolver's root directory.
-    pub fn read_mount_info(&self, offset: usize, writer: &mut VmWriter) -> Result<usize> {
+    ///
-        let mut printer = VmPrinter::new_skip(writer, offset);
+    /// The mounts are collected in depth-first order.
-
+    pub(in crate::fs) fn collect_visible_mounts(&self) -> Vec<Arc<Mount>> {
-        let mut stack = Vec::new();
+        let mut visible = Vec::new();
-        if self.root.is_mount_root() {
+        let mut stack = vec![self.root.mount.clone()];
-            stack.push(self.root.mount.clone());
+        let is_root_mount_root = self.root.is_mount_root();
-        } else {
-            // The root is not a mount root, so we need to find the visible child mounts.
-            let children = self.root.mount.children.read();
-            for child_mount in children.values() {
-                if child_mount
-                    .mountpoint()
-                    .is_some_and(|dentry| dentry.is_equal_or_descendant_of(&self.root.dentry))
-                {
-                    stack.push(child_mount.clone());
-                }
-            }
-        }
 
         while let Some(mount) = stack.pop() {
-            let mount_id = mount.id();
+            let is_root_mount = Arc::ptr_eq(&mount, &self.root.mount);
-            let parent = mount.parent().and_then(|parent| parent.upgrade());
-            let parent_id = parent.as_ref().map_or(mount_id, |p| p.id());
-            let root = mount.root_dentry().path_name();
-            let mount_point = if let Some(parent) = parent {
-                if let Some(mount_point_dentry) = mount.mountpoint() {
-                    self.make_abs_path(&Path::new(parent, mount_point_dentry))
-                        .into_string()
-                } else {
-                    "".to_string()
-                }
-            } else {
-                // No parent means it's the root of the namespace.
-                "/".to_string()
-            };
-            let mount_flags = mount.flags();
-            let fs_type = mount.fs().name();
-            let fs_flags = mount.fs().flags();
 
-            // The following fields are dummy for now.
+            // Add the root mount only if `self` is at the mount root.
-            let major = 0;
+            if !is_root_mount || is_root_mount_root {
-            let minor = 0;
+                visible.push(mount.clone());
-            let source = "none";
+            }
-
-            let entry = MountInfoEntry {
-                mount_id,
-                parent_id,
-                major,
-                minor,
-                root: &root,
-                mount_point: &mount_point,
-                mount_flags,
-                fs_type,
-                source,
-                fs_flags,
-            };
-
-            writeln!(printer, "{}", entry)?;
 
             let children = mount.children.read();
             for child_mount in children.values() {
+                if is_root_mount && !is_root_mount_root {
+                    let Some(mountpoint) = child_mount.mountpoint() else {
+                        continue;
+                    };
+                    if !mountpoint.is_equal_or_descendant_of(&self.root.dentry) {
+                        continue;
+                    }
+                }
                 stack.push(child_mount.clone());
             }
         }
 
-        Ok(printer.bytes_written())
+        visible
-    }
-}
-
-/// A single entry in the mountinfo file.
-struct MountInfoEntry<'a> {
-    /// A unique ID for the mount (but not guaranteed to be unique across reboots).
-    mount_id: usize,
-    /// The ID of the parent mount (or self if it has no parent).
-    parent_id: usize,
-    /// The major device ID of the filesystem.
-    major: u32,
-    /// The minor device ID of the filesystem.
-    minor: u32,
-    /// The root of the mount within the filesystem.
-    root: &'a str,
-    /// The mount point relative to the process's root directory.
-    mount_point: &'a str,
-    /// Per-mount flags.
-    mount_flags: PerMountFlags,
-    /// The type of the filesystem in the form "type[.subtype]".
-    fs_type: &'a str,
-    /// Filesystem-specific information or "none".
-    source: &'a str,
-    /// Per-filesystem flags.
-    fs_flags: FsFlags,
-}
-
-impl core::fmt::Display for MountInfoEntry<'_> {
-    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
-        write!(
-            f,
-            "{} {} {}:{} {} {} {} - {} {} {}",
-            self.mount_id,
-            self.parent_id,
-            self.major,
-            self.minor,
-            &self.root,
-            &self.mount_point,
-            &self.mount_flags,
-            &self.fs_type,
-            &self.source,
-            &self.fs_flags,
-        )
     }
 }
 

kernel/src/fs/procfs/mod.rs

@@ -11,6 +11,7 @@ use self::{
     cpuinfo::CpuInfoFileOps,
     loadavg::LoadAvgFileOps,
     meminfo::MemInfoFileOps,
+    mounts::MountsSymOps,
     pid::PidDirOps,
     self_::SelfSymOps,
     sys::SysDirOps,
@@ -41,6 +42,7 @@ mod cpuinfo;
 mod filesystems;
 mod loadavg;
 mod meminfo;
+mod mounts;
 mod pid;
 mod self_;
 mod stat;
@@ -159,6 +161,7 @@ impl RootDirOps {
         ("filesystems", FileSystemsFileOps::new_inode),
         ("loadavg", LoadAvgFileOps::new_inode),
         ("meminfo", MemInfoFileOps::new_inode),
+        ("mounts", MountsSymOps::new_inode),
         ("self", SelfSymOps::new_inode),
         ("stat", StatFileOps::new_inode),
         ("sys", SysDirOps::new_inode),

kernel/src/fs/procfs/mounts.rs

@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: MPL-2.0
+
+use crate::{
+    fs::{
+        procfs::{ProcSymBuilder, SymOps},
+        utils::{Inode, SymbolicLink, mkmod},
+    },
+    prelude::*,
+};
+
+/// Represents the inode at `/proc/mounts`.
+pub struct MountsSymOps;
+
+impl MountsSymOps {
+    pub fn new_inode(parent: Weak<dyn Inode>) -> Arc<dyn Inode> {
+        // Reference:
+        // <https://elixir.bootlin.com/linux/v6.16.5/source/fs/proc/root.c#L291>
+        // <https://elixir.bootlin.com/linux/v6.16.5/source/fs/proc/generic.c#L466>
+        ProcSymBuilder::new(Self, mkmod!(a+rwx))
+            .parent(parent)
+            .build()
+            .unwrap()
+    }
+}
+
+impl SymOps for MountsSymOps {
+    fn read_link(&self) -> Result<SymbolicLink> {
+        Ok(SymbolicLink::Plain("self/mounts".to_string()))
+    }
+}

kernel/src/fs/procfs/pid/task/mod.rs

@@ -12,8 +12,8 @@ use crate::{
                 cgroup::CgroupFileOps, cmdline::CmdlineFileOps, comm::CommFileOps,
                 environ::EnvironFileOps, exe::ExeSymOps, fd::FdDirOps, gid_map::GidMapFileOps,
                 maps::MapsFileOps, mem::MemFileOps, mountinfo::MountInfoFileOps,
-                oom_score_adj::OomScoreAdjFileOps, stat::StatFileOps, status::StatusFileOps,
+                mounts::MountsFileOps, oom_score_adj::OomScoreAdjFileOps, stat::StatFileOps,
-                uid_map::UidMapFileOps,
+                status::StatusFileOps, uid_map::UidMapFileOps,
             },
             template::{
                 DirOps, ProcDir, ProcDirBuilder, lookup_child_from_table,
@@ -37,6 +37,7 @@ mod gid_map;
 mod maps;
 mod mem;
 mod mountinfo;
+mod mounts;
 mod oom_score_adj;
 mod stat;
 mod status;
@@ -115,6 +116,7 @@ impl TidDirOps {
         ("status", StatusFileOps::new_inode),
         ("uid_map", UidMapFileOps::new_inode),
         ("maps", MapsFileOps::new_inode),
+        ("mounts", MountsFileOps::new_inode),
     ];
 }
 

kernel/src/fs/procfs/pid/task/mountinfo.rs

@@ -1,15 +1,84 @@
 // SPDX-License-Identifier: MPL-2.0
 
+use aster_util::printer::VmPrinter;
+
 use super::TidDirOps;
 use crate::{
     fs::{
+        path::{Mount, Path, PathResolver, PerMountFlags},
         procfs::template::{FileOps, ProcFileBuilder},
-        utils::{Inode, mkmod},
+        utils::{FsFlags, Inode, mkmod},
     },
     prelude::*,
     process::posix_thread::AsPosixThread,
 };
 
+/// A helper function to create the mount point path for a given mount (used by `mounts` and `mountinfo`).
+pub(super) fn make_mount_point_path(
+    is_resolver_root_mount: bool,
+    parent: Option<&Arc<Mount>>,
+    mount: &Mount,
+    path_resolver: &PathResolver,
+) -> String {
+    if is_resolver_root_mount {
+        "/".to_string()
+    } else if let Some(parent) = parent {
+        if let Some(mount_point_dentry) = mount.mountpoint() {
+            path_resolver
+                .make_abs_path(&Path::new(parent.clone(), mount_point_dentry))
+                .into_string()
+        } else {
+            "".to_string()
+        }
+    } else {
+        // No parent means it's the root of the namespace.
+        "/".to_string()
+    }
+}
+
+/// A single entry in the mountinfo file.
+struct MountInfoEntry<'a> {
+    /// A unique ID for the mount (but not guaranteed to be unique across reboots).
+    mount_id: usize,
+    /// The ID of the parent mount (or self if it has no parent).
+    parent_id: usize,
+    /// The major device ID of the filesystem.
+    major: u32,
+    /// The minor device ID of the filesystem.
+    minor: u32,
+    /// The root of the mount within the filesystem.
+    root: &'a str,
+    /// The mount point relative to the process's root directory.
+    mount_point: &'a str,
+    /// Per-mount flags.
+    mount_flags: PerMountFlags,
+    /// The type of the filesystem in the form "type[.subtype]".
+    fs_type: &'a str,
+    /// Filesystem-specific information or "none".
+    source: &'a str,
+    /// Per-filesystem flags.
+    fs_flags: FsFlags,
+}
+
+impl core::fmt::Display for MountInfoEntry<'_> {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        write!(
+            f,
+            "{} {} {}:{} {} {} {} - {} {} {}",
+            self.mount_id,
+            self.parent_id,
+            self.major,
+            self.minor,
+            &self.root,
+            &self.mount_point,
+            &self.mount_flags,
+            &self.fs_type,
+            &self.source,
+            &self.fs_flags,
+        )
+    }
+}
+
 /// Represents the inode at `/proc/[pid]/task/[tid]/mountinfo` (and also `/proc/[pid]/mountinfo`).
 pub struct MountInfoFileOps(TidDirOps);
 
@@ -21,6 +90,62 @@ impl MountInfoFileOps {
             .build()
             .unwrap()
     }
+
+    /// Reads mount information for `/proc/[pid]/mountinfo`.
+    ///
+    /// Provides detailed mount information including mount IDs, parent relationships,
+    /// and device numbers.
+    fn read_mount_info(
+        &self,
+        path_resolver: &PathResolver,
+        offset: usize,
+        writer: &mut VmWriter,
+    ) -> Result<usize> {
+        let mut printer = VmPrinter::new_skip(writer, offset);
+
+        for mount in path_resolver.collect_visible_mounts() {
+            let mount_id = mount.id();
+            let parent = mount.parent().and_then(|parent| parent.upgrade());
+            let parent_id = parent.as_ref().map_or(mount_id, |p| p.id());
+            let is_resolver_root_mount = Arc::ptr_eq(&mount, path_resolver.root().mount_node());
+            let root = if is_resolver_root_mount {
+                path_resolver.root().dentry().path_name()
+            } else {
+                mount.root_dentry().path_name()
+            };
+            let mount_point = make_mount_point_path(
+                is_resolver_root_mount,
+                parent.as_ref(),
+                mount.as_ref(),
+                path_resolver,
+            );
+            let mount_flags = mount.flags();
+            let fs_type = mount.fs().name();
+            let source = mount.source().unwrap_or("none");
+            let fs_flags = mount.fs().flags();
+
+            // The following fields are dummy for now.
+            let major = 0;
+            let minor = 0;
+
+            let entry = MountInfoEntry {
+                mount_id,
+                parent_id,
+                major,
+                minor,
+                root: &root,
+                mount_point: &mount_point,
+                mount_flags,
+                fs_type,
+                source,
+                fs_flags,
+            };
+
+            writeln!(printer, "{}", entry)?;
+        }
+
+        Ok(printer.bytes_written())
+    }
 }
 
 impl FileOps for MountInfoFileOps {
@@ -30,7 +155,6 @@ impl FileOps for MountInfoFileOps {
 
         let fs = posix_thread.read_fs();
         let path_resolver = fs.resolver().read();
-
+        self.read_mount_info(&path_resolver, offset, writer)
-        path_resolver.read_mount_info(offset, writer)
     }
 }

kernel/src/fs/procfs/pid/task/mounts.rs

@@ -0,0 +1,121 @@
+// SPDX-License-Identifier: MPL-2.0
+
+use aster_util::printer::VmPrinter;
+
+use super::TidDirOps;
+use crate::{
+    fs::{
+        path::{PathResolver, PerMountFlags},
+        procfs::{
+            pid::task::mountinfo::make_mount_point_path,
+            template::{FileOps, ProcFileBuilder},
+        },
+        utils::{Inode, mkmod},
+    },
+    prelude::*,
+    process::posix_thread::AsPosixThread,
+};
+
+/// A single entry in the mounts file.
+struct MountEntry<'a> {
+    /// Filesystem-specific information or "none".
+    source: &'a str,
+    /// Mount point relative to the process's root directory.
+    mount_point: &'a str,
+    /// The type of the filesystem in the form "type[.subtype]".
+    fs_type: &'a str,
+    /// Per-mount flags.
+    mount_flags: PerMountFlags,
+    /// The dump field is used by the dump(8) program to determine which
+    /// filesystems need to be dumped.
+    dump: u32,
+    /// The fsck(8) program uses this field.
+    pass: u32,
+}
+
+impl core::fmt::Display for MountEntry<'_> {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        write!(
+            f,
+            "{} {} {} {} {} {}",
+            &self.source,
+            &self.mount_point,
+            &self.fs_type,
+            &self.mount_flags,
+            &self.dump,
+            &self.pass,
+        )
+    }
+}
+
+/// Represents the inode at `/proc/[pid]/task/[tid]/mounts` (and also `/proc/[pid]/mounts`).
+pub struct MountsFileOps(TidDirOps);
+
+impl MountsFileOps {
+    pub fn new_inode(dir: &TidDirOps, parent: Weak<dyn Inode>) -> Arc<dyn Inode> {
+        // Reference: <https://elixir.bootlin.com/linux/v6.16.5/source/fs/proc/base.c#L3351>
+        ProcFileBuilder::new(Self(dir.clone()), mkmod!(a+r))
+            .parent(parent)
+            .build()
+            .unwrap()
+    }
+
+    /// Reads mount information for `/proc/[pid]/mounts` and `/proc/mounts`.
+    ///
+    /// Provides a simplified view of mounted filesystems in the traditional
+    /// `/etc/fstab` format.
+    fn read_mounts(
+        &self,
+        path_resolver: &PathResolver,
+        offset: usize,
+        writer: &mut VmWriter,
+    ) -> Result<usize> {
+        let mut printer = VmPrinter::new_skip(writer, offset);
+
+        for mount in path_resolver.collect_visible_mounts() {
+            let parent = mount.parent().and_then(|parent| parent.upgrade());
+            let is_resolver_root_mount = Arc::ptr_eq(&mount, path_resolver.root().mount_node());
+            let mount_point = make_mount_point_path(
+                is_resolver_root_mount,
+                parent.as_ref(),
+                mount.as_ref(),
+                path_resolver,
+            );
+            let mount_flags = mount.flags();
+            let fs_type = mount.fs().name();
+            let source = mount.source().unwrap_or("none");
+
+            // The dump and pass fields are hardcoded to 0, because the kernel considers them
+            // userspace policy (managed by /etc/fstab) and does not store them in the VFS layer.
+            // This behavior is consistent with Linux.
+            //
+            // Reference: <https://elixir.bootlin.com/linux/v6.16.5/source/fs/proc_namespace.c#L130>.
+            let dump = 0;
+            let pass = 0;
+
+            let entry = MountEntry {
+                source,
+                mount_point: &mount_point,
+                fs_type,
+                mount_flags,
+                dump,
+                pass,
+            };
+
+            writeln!(printer, "{}", entry)?;
+        }
+
+        Ok(printer.bytes_written())
+    }
+}
+
+impl FileOps for MountsFileOps {
+    fn read_at(&self, offset: usize, writer: &mut VmWriter) -> Result<usize> {
+        let thread = self.0.thread();
+        let posix_thread = thread.as_posix_thread().unwrap();
+
+        let fs = posix_thread.read_fs();
+        let path_resolver = fs.resolver().read();
+        self.read_mounts(&path_resolver, offset, writer)
+    }
+}

kernel/src/fs/utils/fs.rs

@@ -150,6 +150,11 @@ pub trait FileSystem: Any + Sync + Send {
     /// Gets the name of this FS type such as `"ext4"` or `"sysfs"`.
     fn name(&self) -> &'static str;
 
+    /// Gets the source of this file system, e.g., the device name or user-provided source string.
+    fn source(&self) -> Option<&str> {
+        None
+    }
+
     /// Syncs the file system.
     fn sync(&self) -> Result<()>;
 

kernel/src/syscall/mount.rs

@@ -6,7 +6,7 @@ use super::SyscallReturn;
 use crate::{
     fs::{
         path::{AT_FDCWD, FsPath, MountPropType, Path, PerMountFlags},
-        registry::FsProperties,
+        registry::{FsProperties, FsType},
         utils::{FileSystem, FsFlags, InodeType},
     },
     prelude::*,
@@ -192,22 +192,44 @@ fn do_new_mount(
         return_errno_with_message!(Errno::ENOTDIR, "mountpoint must be directory");
     };
 
-    let fs_type = ctx
+    let fs_type = {
-        .user_space()
+        let fs_type_cstr = ctx
-        .read_cstring(fs_type_addr, MAX_FILENAME_LEN)?;
+            .user_space()
-    if fs_type.is_empty() {
+            .read_cstring(fs_type_addr, MAX_FILENAME_LEN)?;
-        return_errno_with_message!(Errno::EINVAL, "fs_type is empty");
+        if fs_type_cstr.is_empty() {
-    }
+            return_errno_with_message!(Errno::EINVAL, "empty file system type");
-    let fs = get_fs(src_name_addr, flags, fs_type, data_addr, ctx)?;
+        }
-    target_path.mount(fs, flags.into(), ctx)?;
+
+        let fs_type_str = fs_type_cstr
+            .to_str()
+            .map_err(|_| Error::with_message(Errno::ENODEV, "invalid file system type"))?;
+        crate::fs::registry::look_up(fs_type_str).ok_or(Error::with_message(
+            Errno::ENODEV,
+            "the filesystem is not configured in the kernel",
+        ))?
+    };
+
+    let source = if src_name_addr == 0 {
+        None
+    } else {
+        let source = ctx
+            .user_space()
+            .read_cstring(src_name_addr, MAX_FILENAME_LEN)?
+            .to_string_lossy()
+            .into_owned();
+        Some(source)
+    };
+
+    let fs = open_fs(source.as_deref(), flags, fs_type, data_addr, ctx)?;
+    target_path.mount(fs, flags.into(), source, ctx)?;
     Ok(())
 }
 
-/// Gets the filesystem by fs_type and devname.
+/// Gets the filesystem by fs_type and dev_name.
-fn get_fs(
+fn open_fs(
-    src_name_addr: Vaddr,
+    dev_name: Option<&str>,
     flags: MountFlags,
-    fs_type: CString,
+    fs_type: &dyn FsType,
     data_addr: Vaddr,
     ctx: &Context,
 ) -> Result<Arc<dyn FileSystem>> {
@@ -218,18 +240,10 @@ fn get_fs(
         Some(user_space.read_cstring(data_addr, MAX_FILENAME_LEN)?)
     };
 
-    let fs_type = fs_type
-        .to_str()
-        .map_err(|_| Error::with_message(Errno::ENODEV, "invalid file system type"))?;
-    let fs_type = crate::fs::registry::look_up(fs_type).ok_or(Error::with_message(
-        Errno::ENODEV,
-        "the filesystem is not configured in the kernel",
-    ))?;
-
     let disk = if fs_type.properties().contains(FsProperties::NEED_DISK) {
-        let devname = user_space.read_cstring(src_name_addr, MAX_FILENAME_LEN)?;
+        let dev_name = dev_name
-        let path = devname.to_string_lossy();
+            .ok_or_else(|| Error::with_message(Errno::EINVAL, "the source is not specified"))?;
-        let fs_path = FsPath::from_fd_and_path(AT_FDCWD, path.as_ref())?;
+        let fs_path = FsPath::from_fd_and_path(AT_FDCWD, dev_name)?;
         let path = ctx
             .thread_local
             .borrow_fs()

test/initramfs/src/syscall/gvisor/blocklists/proc_test

@@ -7,7 +7,6 @@ ProcCpuinfo.RequiredFieldsArePresent
 ProcCpuinfo.DeniesWriteNonRoot
 ProcFilesystems.OverflowID
 ProcFilesystems.PresenceOfShmMaxMniAll
-ProcMounts.IsSymlink
 ProcPid.AccessDeny
 ProcPidCwd.Subprocess
 ProcPidRoot.Subprocess
@@ -31,8 +30,6 @@ ProcSelfFdInfo.Flags
 # TODO: Mappings created with only `PROT_WRITE` should be shown as `-w-`.
 ProcSelfMaps.Map2
 ProcSelfMaps.MapUnmap
-ProcSelfMounts.ContainsProcfsEntry
-ProcSelfMounts.RequiredFieldsArePresent
 ProcSelfRoot.IsRoot
 ProcSelfStat.PopulateWriteRSS
 ProcSysKernelHostname.Exists