Add ReadBufferFromFileBase::isRegularLocalFile()

src/IO/AsynchronousReadBufferFromFile.h

@@ -45,6 +45,8 @@ class AsynchronousReadBufferFromFile : public AsynchronousReadBufferFromFileDesc
     {
         return file_name;
     }
+
+    bool isRegularLocalFile(size_t * /* out_view_offset */) override { return true; }
 };
 
 /** Similar to AsynchronousReadBufferFromFile but also transparently shares open file descriptors.
@@ -79,6 +81,8 @@ class AsynchronousReadBufferFromFileWithDescriptorsCache : public AsynchronousRe
     {
         return file_name;
     }
+
+    bool isRegularLocalFile(size_t * /* out_view_offset */) override { return true; }
 };
 
 }

src/IO/MMapReadBufferFromFile.cpp

@@ -40,6 +40,13 @@ std::string MMapReadBufferFromFile::getFileName() const
 }
 
 
+bool MMapReadBufferFromFile::isRegularLocalFile(size_t * out_view_offset)
+{
+    *out_view_offset = mapped.getOffset();
+    return true;
+}
+
+
 MMapReadBufferFromFile::MMapReadBufferFromFile(const std::string & file_name_, size_t offset, size_t length_)
     : file_name(file_name_)
 {

src/IO/MMapReadBufferFromFile.h

@@ -27,6 +27,8 @@ class MMapReadBufferFromFile : public MMapReadBufferFromFileDescriptor
 
     std::string getFileName() const override;
 
+    bool isRegularLocalFile(size_t * out_view_offset) override;
+
 private:
     int fd = -1;
     std::string file_name;

src/IO/MMapReadBufferFromFileWithCache.h

@@ -20,6 +20,8 @@ class MMapReadBufferFromFileWithCache : public ReadBufferFromFileBase
     std::string getFileName() const override;
     off_t seek(off_t offset, int whence) override;
 
+    bool isRegularLocalFile(size_t * /* out_view_offset */) override { return true; }
+
 private:
     MMappedFileCache::MappedPtr mapped;
 

src/IO/ReadBufferFromFile.h

@@ -53,6 +53,8 @@ class ReadBufferFromFile : public ReadBufferFromFileDescriptor
     }
 
     size_t getFileOffsetOfBufferEnd() const override { return file_offset_of_buffer_end; }
+
+    bool isRegularLocalFile(size_t * /* out_view_offset */) override { return true; }
 };
 
 
@@ -103,6 +105,8 @@ class ReadBufferFromFilePReadWithDescriptorsCache : public ReadBufferFromFileDes
     {
         return file_name;
     }
+
+    bool isRegularLocalFile(size_t * /* out_view_offset */) override { return true; }
 };
 
 }

src/IO/ReadBufferFromFileBase.h

@@ -54,6 +54,12 @@ class ReadBufferFromFileBase : public BufferWithOwnMemory<SeekableReadBuffer>, p
 
     void setProgressCallback(ContextPtr context);
 
+    /// Returns true if this file is on local filesystem, and getFileName() is its path.
+    /// I.e. it can be read using open() or mmap(). If this buffer is a "view" into a subrange of the
+    /// file, *out_view_offset is set to the start of that subrange, i.e. the difference between actual
+    /// file offset and what getPosition() returns.
+    virtual bool isRegularLocalFile(size_t * /* out_view_offset */ = nullptr) { return false; }
+
 protected:
     std::optional<size_t> file_size;
     ProfileCallback profile_callback;