From 9a76ca1888668356478a1ed74c7f0511772c57eb Mon Sep 17 00:00:00 2001
From: LI Qing <geding.lq@antgroup.com>
Date: Thu, 13 May 2021 17:38:43 +0800
Subject: [PATCH] Add support for '/proc/[pid]/root'

---
 src/libos/src/fs/fs_view.rs          | 18 ++++++++++++------
 src/libos/src/fs/procfs/pid_inode.rs | 20 ++++++++++++++++++++
 test/procfs/main.c                   | 11 +++++++++++
 3 files changed, 43 insertions(+), 6 deletions(-)

diff --git a/src/libos/src/fs/fs_view.rs b/src/libos/src/fs/fs_view.rs
index 356025cb..248d38b2 100644
--- a/src/libos/src/fs/fs_view.rs
+++ b/src/libos/src/fs/fs_view.rs
@@ -3,14 +3,20 @@ use super::*;
 
 #[derive(Debug, Clone)]
 pub struct FsView {
+    root: String,
     cwd: String,
 }
 
 impl FsView {
     pub fn new() -> FsView {
-        Self {
-            cwd: "/".to_owned(),
-        }
+        let root = String::from("/");
+        let cwd = root.clone();
+        Self { root, cwd }
+    }
+
+    /// Get the root directory
+    pub fn root(&self) -> &str {
+        &self.root
     }
 
     /// Get the current working directory.
@@ -203,8 +209,8 @@ impl FsView {
 
 impl Default for FsView {
     fn default() -> Self {
-        Self {
-            cwd: "/".to_owned(),
-        }
+        let root = String::from("/");
+        let cwd = root.clone();
+        Self { root, cwd }
     }
 }
diff --git a/src/libos/src/fs/procfs/pid_inode.rs b/src/libos/src/fs/procfs/pid_inode.rs
index 630356fe..a1b01502 100644
--- a/src/libos/src/fs/procfs/pid_inode.rs
+++ b/src/libos/src/fs/procfs/pid_inode.rs
@@ -38,6 +38,10 @@ impl LockedPidDirINode {
         // fd
         let fd_inode = LockedProcFdDirINode::new(&file.process_ref, file.this.upgrade().unwrap());
         file.entries.insert(String::from("fd"), fd_inode);
+        // root
+        let root_inode = ProcRootSymINode::new(&file.process_ref);
+        file.entries.insert(String::from("root"), root_inode);
+
         Ok(())
     }
 }
@@ -166,6 +170,22 @@ impl ProcINode for ProcCwdSymINode {
     }
 }
 
+pub struct ProcRootSymINode(ProcessRef);
+
+impl ProcRootSymINode {
+    pub fn new(process_ref: &ProcessRef) -> Arc<dyn INode> {
+        Arc::new(SymLink::new(Self(Arc::clone(process_ref))))
+    }
+}
+
+impl ProcINode for ProcRootSymINode {
+    fn generate_data_in_bytes(&self) -> vfs::Result<Vec<u8>> {
+        let main_thread = self.0.main_thread().ok_or(FsError::EntryNotFound)?;
+        let fs = main_thread.fs().lock().unwrap();
+        Ok(fs.root().to_owned().into_bytes())
+    }
+}
+
 pub struct FdSymINode(FileRef);
 
 impl FdSymINode {
diff --git a/test/procfs/main.c b/test/procfs/main.c
index cc200bee..0a1ee0c9 100644
--- a/test/procfs/main.c
+++ b/test/procfs/main.c
@@ -66,6 +66,16 @@ static int test_readlink_from_proc_self_cwd() {
     return 0;
 }
 
+static int test_readlink_from_proc_self_root() {
+    char root_buf[PATH_MAX] = { 0 };
+    const char *proc_root = "/proc/self/root";
+
+    if (test_readlink_from_procfs(proc_root, root_buf, PATH_MAX, "/") < 0) {
+        THROW_ERROR("failed to call test_readlink_from_procfs");
+    }
+    return 0;
+}
+
 static int test_read_from_proc_self_cmdline() {
     char absolute_path[PATH_MAX] = { 0 };
     const char *proc_cmdline = "/proc/self/cmdline";
@@ -126,6 +136,7 @@ static int test_read_from_proc_cpuinfo() {
 static test_case_t test_cases[] = {
     TEST_CASE(test_readlink_from_proc_self_exe),
     TEST_CASE(test_readlink_from_proc_self_cwd),
+    TEST_CASE(test_readlink_from_proc_self_root),
     TEST_CASE(test_read_from_proc_self_cmdline),
     TEST_CASE(test_read_from_proc_meminfo),
     TEST_CASE(test_read_from_proc_cpuinfo),