Kernel: Expose info about source devices of mounts in /proc/df

Author: https://github.com/bugaevc
Commit: https://github.com/SerenityOS/serenity/commit/fde8f7f538b
Pull-request: https://github.com/SerenityOS/serenity/pull/456
Reviewed-by: https://github.com/awesomekling ✅

Kernel/Devices/Device.cpp

@@ -14,7 +14,12 @@ Device::~Device()
     VFS::the().unregister_device({}, *this);
 }
 
-String Device::absolute_path(const FileDescription&) const
+String Device::absolute_path() const
 {
     return String::format("device:%u,%u (%s)", m_major, m_minor, class_name());
 }
+
+String Device::absolute_path(const FileDescription&) const
+{
+    return absolute_path();
+}

Kernel/Devices/Device.h

@@ -20,6 +20,7 @@ public:
     unsigned minor() const { return m_minor; }
 
     virtual String absolute_path(const FileDescription&) const override;
+    virtual String absolute_path() const;
 
     uid_t uid() const { return m_uid; }
     uid_t gid() const { return m_gid; }

Kernel/FileSystem/DiskBackedFileSystem.h

@@ -7,6 +7,8 @@ class DiskBackedFS : public FS {
 public:
     virtual ~DiskBackedFS() override;
 
+    virtual bool is_disk_backed() const override { return true; }
+
     DiskDevice& device() { return *m_device; }
     const DiskDevice& device() const { return *m_device; }
 

Kernel/FileSystem/FileSystem.h

@@ -65,6 +65,8 @@ public:
 
     int block_size() const { return m_block_size; }
 
+    virtual bool is_disk_backed() const { return false; }
+
 protected:
     FS();
 

Kernel/FileSystem/ProcFS.cpp

@@ -9,6 +9,7 @@
 #include <AK/JsonValue.h>
 #include <Kernel/Arch/i386/CPU.h>
 #include <Kernel/FileSystem/Custody.h>
+#include <Kernel/FileSystem/DiskBackedFileSystem.h>
 #include <Kernel/FileSystem/FileDescription.h>
 #include <Kernel/FileSystem/VirtualFileSystem.h>
 #include <Kernel/KBufferBuilder.h>
@@ -502,7 +503,13 @@ Optional<KBuffer> procfs$df(InodeIdentifier)
         fs_object.set("mount_point", mount.absolute_path());
         fs_object.set("block_size", fs.block_size());
         fs_object.set("readonly", fs.is_readonly());
-        json.append(fs_object);
+
+        if (fs.is_disk_backed())
+            fs_object.set("device", static_cast<const DiskBackedFS&>(fs).device().absolute_path());
+        else
+            fs_object.set("device", nullptr);
+
+        json.append(move(fs_object));
     });
     return json.serialized<KBufferBuilder>();
 }