AK: Make MappedFile store why it is invalid

This makes AK::MappedFile save the errno either open() or mmap() failed
with.

2 files changed, 12 insertions, 2 deletions

diff --git a/AK/MappedFile.cpp b/AK/MappedFile.cpp
index 3f3afb8691..7fcc2c5410 100644
--- a/AK/MappedFile.cpp
+++ b/AK/MappedFile.cpp
@@ -41,6 +41,7 @@ MappedFile::MappedFile(const StringView& file_name)
     int fd = open_with_path_length(file_name.characters_without_null_termination(), file_name.length(), O_RDONLY | O_CLOEXEC, 0);
 
     if (fd == -1) {
+        m_errno = errno;
         perror("open");
         return;
     }
@@ -50,8 +51,10 @@ MappedFile::MappedFile(const StringView& file_name)
     m_size = st.st_size;
     m_map = mmap(nullptr, m_size, PROT_READ, MAP_SHARED, fd, 0);
 
-    if (m_map == MAP_FAILED)
+    if (m_map == MAP_FAILED) {
+        m_errno = errno;
         perror("mmap");
+    }
 
 #ifdef DEBUG_MAPPED_FILE
     dbgprintf("MappedFile{%s} := { fd=%d, m_size=%u, m_map=%p }\n", file_name.characters(), fd, m_size, m_map);
diff --git a/AK/MappedFile.h b/AK/MappedFile.h
index bdf3b78406..a7649e78a5 100644
--- a/AK/MappedFile.h
+++ b/AK/MappedFile.h
@@ -33,8 +33,9 @@ namespace AK {
 
 class MappedFile {
     AK_MAKE_NONCOPYABLE(MappedFile);
+
 public:
-    MappedFile() {}
+    MappedFile() { }
     explicit MappedFile(const StringView& file_name);
     MappedFile(MappedFile&&);
     ~MappedFile();
@@ -42,6 +43,11 @@ public:
     MappedFile& operator=(MappedFile&&);
 
     bool is_valid() const { return m_map != (void*)-1; }
+    int errno_if_invalid() const
+    {
+        ASSERT(!is_valid());
+        return m_errno;
+    }
     void unmap();
 
     void* data() { return m_map; }
@@ -51,6 +57,7 @@ public:
 private:
     size_t m_size { 0 };
     void* m_map { (void*)-1 };
+    int m_errno { 0 };
 };
 
 }