libos+rm: Add recursive removal of directories

apps/rm.cpp

@@ -4,12 +4,16 @@
 Result<int> luna_main(int argc, char** argv)
 {
     StringView path;
+    bool recursive;
 
     os::ArgumentParser parser;
     parser.add_positional_argument(path, "path"_sv, true);
+    parser.add_switch_argument(recursive, 'r', "recursive"_sv);
     parser.parse(argc, argv);
 
-    TRY(os::FileSystem::remove(path));
+    if (!recursive) TRY(os::FileSystem::remove(path));
+    else
+        TRY(os::FileSystem::remove_tree(path));
 
     return 0;
 }

libos/include/os/FileSystem.h

@@ -14,6 +14,10 @@ namespace os
         Result<void> create_directory(StringView path, mode_t mode);
 
         Result<void> remove(StringView path);
+        Result<void> removeat(int dirfd, StringView path);
+
+        Result<void> remove_tree(StringView path);
+        Result<void> remove_tree_at(int dirfd, StringView path);
 
         Result<String> working_directory();
         Result<String> home_directory();

libos/src/FileSystem.cpp

@@ -1,6 +1,7 @@
 #include <luna/String.h>
 #include <os/FileSystem.h>
 
+#include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <pwd.h>
@@ -38,11 +39,50 @@ namespace os::FileSystem
 
     Result<void> remove(StringView path)
     {
-        long rc = syscall(SYS_unlinkat, AT_FDCWD, path.chars(), 0);
+        return removeat(AT_FDCWD, path);
+    }
+
+    Result<void> removeat(int dirfd, StringView path)
+    {
+        long rc = syscall(SYS_unlinkat, dirfd, path.chars(), 0);
 
         return Result<void>::from_syscall(rc);
     }
 
+    Result<void> remove_tree(StringView path)
+    {
+        return remove_tree_at(AT_FDCWD, path);
+    }
+
+    Result<void> remove_tree_at(int dirfd, StringView path)
+    {
+        auto rc = removeat(dirfd, path);
+        if (!rc.has_error()) return {};
+        if (rc.error() != ENOTEMPTY) return rc.release_error();
+
+        DIR* dp = opendir(path.chars());
+        if (!dp) return err(errno);
+
+        Vector<String> entries;
+
+        // FIXME: This is done because the kernel doesn't appreciate us deleting entries while iterating over
+        // directories. This means that we have to iterate first, then delete.
+
+        struct dirent* ent;
+        while ((ent = readdir(dp)))
+        {
+            if ("."_sv == ent->d_name || ".."_sv == ent->d_name) continue;
+            auto entry = TRY(String::from_cstring(ent->d_name));
+            TRY(entries.try_append(move(entry)));
+        }
+
+        for (const auto& entry : entries) { TRY(remove_tree_at(dp->_fd, entry.view())); }
+
+        closedir(dp);
+
+        return removeat(dirfd, path);
+    }
+
     Result<String> working_directory()
     {
         char* ptr = getcwd(NULL, 0);