tmpfs: Implement FileInode read() and write()

kernel/src/fs/VFS.h

@@ -21,6 +21,11 @@ namespace VFS
 
         virtual Result<SharedPtr<Inode>> create_subdirectory(const char* name) = 0;
 
+        // File-specific methods
+        virtual Result<usize> read(u8* buf, usize offset, usize length) const = 0;
+
+        virtual Result<usize> write(const u8* buf, usize offset, usize length) = 0;
+
         // Generic methods
         virtual FileSystem& fs() const = 0;
 

kernel/src/fs/tmpfs/FileSystem.cpp

@@ -81,4 +81,37 @@ namespace TmpFS
 
         return inode;
     }
+
+    Result<usize> FileInode::read(u8* buf, usize offset, usize length) const
+    {
+        if (length == 0) return 0;
+
+        if (offset > m_data_buffer.size()) return 0;
+        if (offset + length > m_data_buffer.size()) length = m_data_buffer.size() - offset;
+
+        memcpy(buf, m_data_buffer.data() + offset, length);
+
+        return length;
+    }
+
+    Result<usize> FileInode::write(const u8* buf, usize offset, usize length)
+    {
+        if (length == 0) return 0;
+
+        if (offset > m_data_buffer.size())
+        {
+            // Fill the in-between space with zeroes.
+            usize old_size = m_data_buffer.size();
+            usize zeroes = offset - old_size;
+
+            TRY(m_data_buffer.try_resize(offset));
+
+            memset(m_data_buffer.data() + old_size, 0, zeroes);
+        }
+
+        u8* slice = TRY(m_data_buffer.slice(offset, length));
+        memcpy(slice, buf, length);
+
+        return length;
+    }
 }

kernel/src/fs/tmpfs/FileSystem.h

@@ -2,6 +2,7 @@
 #include "fs/VFS.h"
 #include <luna/Atomic.h>
 #include <luna/Badge.h>
+#include <luna/Buffer.h>
 #include <luna/StaticString.h>
 #include <luna/Vector.h>
 
@@ -58,10 +59,15 @@ namespace TmpFS
             return m_inode_number;
         }
 
+        Result<usize> read(u8*, usize, usize) const override;
+
+        Result<usize> write(const u8*, usize, usize) override;
+
         virtual ~FileInode() = default;
 
       private:
         VFS::FileSystem* m_fs;
+        Buffer m_data_buffer;
         usize m_inode_number;
     };
 
@@ -87,6 +93,16 @@ namespace TmpFS
 
         Result<SharedPtr<VFS::Inode>> find(const char* name) const override;
 
+        Result<usize> read(u8*, usize, usize) const override
+        {
+            return err(EISDIR);
+        }
+
+        Result<usize> write(const u8*, usize, usize) override
+        {
+            return err(EISDIR);
+        }
+
         VFS::FileSystem& fs() const override
         {
             return *m_fs;

kernel/src/main.cpp

@@ -75,6 +75,14 @@ static Result<void> try_init_vfs()
 
     kinfoln("/etc/passwd's inode number: %zu", passwd.inode_number());
 
+    const char* data = "hello, world!";
+    TRY(passwd.write((const u8*)data, 0, 14));
+
+    char output[14];
+    TRY(passwd.read((u8*)output, 0, 14));
+
+    kinfoln("/etc/passwd contents: '%s'", output);
+
     return {};
 }
 

libluna/include/luna/Buffer.h

@@ -15,7 +15,9 @@ class Buffer
 
     Result<void> try_resize(usize new_size);
 
-    Result<u8*> create_slice_at_end(usize size);
+    Result<u8*> slice_at_end(usize size);
+
+    Result<u8*> slice(usize offset, usize size);
 
     u8* data()
     {
@@ -27,6 +29,16 @@ class Buffer
         return m_data;
     }
 
+    u8* end()
+    {
+        return m_data + m_size;
+    }
+
+    const u8* end() const
+    {
+        return m_data + m_size;
+    }
+
     usize size() const
     {
         return m_size;

libluna/src/Buffer.cpp

@@ -32,9 +32,15 @@ Result<void> Buffer::try_resize(usize new_size)
     return {};
 }
 
-Result<u8*> Buffer::create_slice_at_end(usize size)
+Result<u8*> Buffer::slice_at_end(usize size)
 {
     usize old_size = m_size;
     TRY(try_resize(m_size + size));
     return m_data + old_size;
 }
+
+Result<u8*> Buffer::slice(usize offset, usize size)
+{
+    if (offset + size > m_size) { TRY(try_resize(offset + size)); }
+    return m_data + offset;
+}