Userland: Reimplement the mount command

This new version can do three things:

* When invoked as `mount`, it will print out a list of mounted filesystem,
* When invoked as `mount -a`, it will try to mount filesystems
  listed in /etc/fstab,
* When invoked as `mount device mountpoint -t fstype`, it will mount that
  device on that mountpoint. If not specified, fstype defaults to ext2.

Userland/mount.cpp

@@ -1,28 +1,114 @@
+#include <AK/JsonArray.h>
+#include <AK/JsonObject.h>
+#include <AK/JsonValue.h>
 #include <LibCore/CArgsParser.h>
+#include <LibCore/CFile.h>
 #include <stdio.h>
 #include <unistd.h>
 
+bool mount_all()
+{
+    // Mount all filesystems listed in /etc/fstab.
+    dbg() << "Mounting all filesystems...";
+
+    CFile fstab { "/etc/fstab" };
+    if (!fstab.open(CIODevice::OpenMode::ReadOnly)) {
+        fprintf(stderr, "Failed to open /etc/fstab: %s\n", fstab.error_string());
+        return false;
+    }
+
+    bool all_ok = true;
+    while (fstab.can_read_line()) {
+        ByteBuffer buffer = fstab.read_line(1024);
+        StringView line_view = (const char*)buffer.data();
+
+        // Trim the trailing newline, if any.
+        if (line_view.length() > 0 && line_view[line_view.length() - 1] == '\n')
+            line_view = line_view.substring_view(0, line_view.length() - 1);
+        String line = line_view;
+
+        Vector<String> parts = line.split('\t');
+        if (parts.size() < 3) {
+            fprintf(stderr, "Invalid fstab entry: %s\n", line.characters());
+            all_ok = false;
+            continue;
+        }
+
+        const char* devname = parts[0].characters();
+        const char* mountpoint = parts[1].characters();
+        const char* fstype = parts[2].characters();
+
+        if (strcmp(mountpoint, "/") == 0) {
+            dbg() << "Skipping mounting root";
+            continue;
+        }
+
+        dbg() << "Mounting " << devname << "(" << fstype << ")"
+              << " on " << mountpoint;
+        int rc = mount(devname, mountpoint, fstype);
+        if (rc != 0) {
+            fprintf(stderr, "Failed to mount %s (%s) on %s: %s\n", devname, fstype, mountpoint, strerror(errno));
+            all_ok = false;
+            continue;
+        }
+    }
+
+    return all_ok;
+}
+
+bool print_mounts()
+{
+    // Output info about currently mounted filesystems.
+    CFile df("/proc/df");
+    if (!df.open(CIODevice::ReadOnly)) {
+        fprintf(stderr, "Failed to open /proc/df: %s\n", df.error_string());
+        return false;
+    }
+
+    auto content = df.read_all();
+    auto json = JsonValue::from_string(content).as_array();
+
+    json.for_each([](auto& value) {
+        auto fs_object = value.as_object();
+        auto class_name = fs_object.get("class_name").to_string();
+        auto mount_point = fs_object.get("mount_point").to_string();
+        auto device = fs_object.get("device").as_string_or(class_name);
+
+        printf("%s on %s type %s\n", device.characters(), mount_point.characters(), class_name.characters());
+    });
+
+    return true;
+}
+
 int main(int argc, char** argv)
 {
     CArgsParser args_parser("mount");
     args_parser.add_arg("devname", "device path");
     args_parser.add_arg("mountpoint", "mount point");
-    args_parser.add_arg("fstype", "file system type");
+    args_parser.add_arg("t", "fstype", "file system type");
+    args_parser.add_arg("a", "mount all systems listed in /etc/fstab");
     CArgsParserResult args = args_parser.parse(argc, argv);
 
-    if (argc < 3 || argc > 4) {
-        args_parser.print_usage();
+    if (args.is_present("a")) {
+        return mount_all() ? 0 : 1;
+    }
+
+    switch (args.get_single_values().size()) {
+    case 0:
+        return print_mounts() ? 0 : 1;
+    case 2: {
+        String devname = args.get_single_values()[0];
+        String mountpoint = args.get_single_values()[1];
+        String fstype = args.is_present("t") ? args.get("t") : "ext2";
+
+        if (mount(devname.characters(), mountpoint.characters(), fstype.characters()) < 0) {
+            perror("mount");
+            return 1;
+        }
         return 0;
     }
-
-    const char* devname = argv[1];
-    const char* mountpoint = argv[2];
-    const char* fstype = argc == 4 ? argv[3] : "ext2";
-
-    if (mount(devname, mountpoint, fstype) < 0) {
-        perror("mount");
+    default:
+        args_parser.print_usage();
         return 1;
     }
-
-    return 0;
 }