feat(syscall/fs): handle non-cwd fd {open,chdir}

* Handle non-AT_FDCWD file descriptors for {open,chdir} system calls.
  The updated signature and behaviour has also been updated in the mlibc
  patches.

Signed-off-by: Anhad Singh <[email protected]>

patches/mlibc/jinx-working-patch.patch

@@ -15,3 +15,58 @@ index 3474615..d06f130 100644
  }
 
  char **backtrace_symbols(void *const *, int) {
+diff --git mlibc-clean/sysdeps/aero/generic/aero.cpp mlibc-workdir/sysdeps/aero/generic/aero.cpp
+index 80f9c6f..897986d 100644
+--- mlibc-clean/sysdeps/aero/generic/aero.cpp
++++ mlibc-workdir/sysdeps/aero/generic/aero.cpp
+@@ -200,14 +200,19 @@ int sys_getcwd(char *buffer, size_t size) {
+     return 0;
+ }
+
+-int sys_chdir(const char *path) {
+-    auto result = syscall(SYS_CHDIR, path, strlen(path));
++static int sys_chdir_impl(int fd, const char *path) {
++  auto ret = syscall(SYS_CHDIR, fd, path, strlen(path));
++  if(int e = sc_error(ret); e)
++    return e;
++  return 0;
++}
+
+-    if (result < 0) {
+-        return -result;
+-    }
++int sys_chdir(const char *path) {
++  return sys_chdir_impl(AT_FDCWD, path);
++}
+
+-    return 0;
++int sys_fchdir(int fd) {
++  return sys_chdir_impl(fd, "");
+ }
+
+ int sys_gethostname(char *buffer, size_t bufsize) {
+diff --git mlibc-clean/sysdeps/aero/generic/filesystem.cpp mlibc-workdir/sysdeps/aero/generic/filesystem.cpp
+index 95c49b9..9416be7 100644
+--- mlibc-clean/sysdeps/aero/generic/filesystem.cpp
++++ mlibc-workdir/sysdeps/aero/generic/filesystem.cpp
+@@ -69,13 +69,14 @@ int sys_seek(int fd, off_t offset, int whence, off_t *new_offset) {
+ }
+
+ int sys_open(const char *filename, int flags, mode_t mode, int *fd) {
+-    auto result = syscall(SYS_OPEN, 0, filename, strlen(filename), flags);
+-
+-    if (result < 0) {
+-        return -result;
+-    }
++    return sys_openat(AT_FDCWD, filename, flags, mode, fd);
++}
+
+-    *fd = result;
++int sys_openat(int dirfd, const char *path, int flags, mode_t mode, int *fd) {
++    auto ret = syscall(SYS_OPEN, dirfd, path, strlen(path), flags, mode);
++    if (int e = sc_error(ret); e)
++        return e;
++    *fd = ret;
+     return 0;
+ }
+

src/aero_kernel/src/syscall/fs.rs

@@ -102,22 +102,19 @@ pub fn read(fd: FileDescriptor, buffer: &mut [u8]) -> Result<usize, SyscallError
 }
 
 #[syscall]
-pub fn open(fd: usize, path: &Path, mode: usize) -> Result<usize, SyscallError> {
-    let dir = match fd as isize {
-        0 => {
-            if !path.is_absolute() {
-                scheduler::get_scheduler().current_task().cwd_dirent()
-            } else {
-                crate::fs::root_dir().clone()
-            }
-        }
-
-        _ => {
-            todo!()
+pub fn open(fd: usize, path: &Path, flags: usize, _mode: usize) -> Result<usize, SyscallError> {
+    let current_thread = scheduler::current_thread();
+    let at = match fd as isize {
+        AT_FDCWD if !path.is_absolute() => current_thread.cwd_dirent(),
+        _ if !path.is_absolute() => {
+            let ent = FileDescriptor::from_usize(fd).handle()?.inode.clone();
+            assert!(ent.inode().metadata()?.is_directory());
+            ent
         }
+        _ => fs::root_dir().clone(),
     };
 
-    let mut flags = OpenFlags::from_bits(mode).ok_or(SyscallError::EINVAL)?;
+    let mut flags = OpenFlags::from_bits(flags).ok_or(SyscallError::EINVAL)?;
 
     if !flags.intersects(OpenFlags::O_RDONLY | OpenFlags::O_RDWR | OpenFlags::O_WRONLY) {
         flags.insert(OpenFlags::O_RDONLY);
@@ -129,7 +126,7 @@ pub fn open(fd: usize, path: &Path, mode: usize) -> Result<usize, SyscallError>
         lookup_mode = LookupMode::Create;
     }
 
-    let inode = fs::lookup_path_with(dir, path, lookup_mode, true)?;
+    let inode = fs::lookup_path_with(at, path, lookup_mode, true)?;
 
     if flags.contains(OpenFlags::O_DIRECTORY) && !inode.inode().metadata()?.is_directory() {
         return Err(SyscallError::ENOTDIR);
@@ -139,9 +136,7 @@ pub fn open(fd: usize, path: &Path, mode: usize) -> Result<usize, SyscallError>
         inode.inode().truncate(0)?;
     }
 
-    Ok(scheduler::current_thread()
-        .file_table
-        .open_file(inode.clone(), flags)?)
+    Ok(current_thread.file_table.open_file(inode.clone(), flags)?)
 }
 
 #[syscall]
@@ -183,15 +178,29 @@ pub fn close(fd: FileDescriptor) -> Result<usize, SyscallError> {
 }
 
 #[syscall]
-pub fn chdir(path: &str) -> Result<usize, SyscallError> {
-    let inode = fs::lookup_path(Path::new(path))?;
+pub fn chdir(fd: usize, path: &Path) -> Result<usize, SyscallError> {
+    let current_thread = scheduler::current_thread();
+    let at = match fd as isize {
+        AT_FDCWD if !path.is_absolute() => current_thread.cwd_dirent(),
+        _ if !path.is_absolute() => {
+            let ent = FileDescriptor::from_usize(fd).handle()?.inode.clone();
+            assert!(ent.inode().metadata()?.is_directory());
+            ent
+        }
+        _ => fs::root_dir().clone(),
+    };
 
-    if !inode.inode().metadata()?.is_directory() {
-        // A component of path is not a directory.
+    if path.is_empty() {
+        current_thread.set_cwd(at);
+        return Ok(0);
+    }
+
+    let ent = fs::lookup_path_with(at, path, LookupMode::None, true)?;
+    if !ent.inode().metadata()?.is_directory() {
         return Err(SyscallError::ENOTDIR);
     }
 
-    scheduler::get_scheduler().current_task().set_cwd(inode);
+    current_thread.set_cwd(ent);
     Ok(0)
 }
 

src/aero_kernel/src/syscall/mod.rs

@@ -207,12 +207,12 @@ pub fn generic_do_syscall(
         SYS_GETPGID => process::getpgid(b),
 
         SYS_READ => fs::read(b, c, d),
-        SYS_OPEN => fs::open(b, c, d, e),
+        SYS_OPEN => fs::open(b, c, d, e, f),
         SYS_CLOSE => fs::close(b),
         SYS_WRITE => fs::write(b, c, d),
         SYS_GETDENTS => fs::getdents(b, c, d),
         SYS_GETCWD => fs::getcwd(b, c),
-        SYS_CHDIR => fs::chdir(b, c),
+        SYS_CHDIR => fs::chdir(b, c, d),
         SYS_MKDIR_AT => fs::mkdirat(b, c, d),
         SYS_RMDIR => fs::rmdir(b, c),
         SYS_IOCTL => fs::ioctl(b, c, d),