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Kernel: Implement O_DIRECT open() flag to bypass disk caches

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Files opened with O_DIRECT will now bypass the disk cache in read/write
operations (though metadata operations will still hit the disk cache.)

This will allow us to test actual disk performance instead of testing
disk *cache* performance, if that's what we want. :^)

There's room for improvment here, we're very aggressively flushing any
dirty cache entries for the specific block before reading/writing that
block. This is done by walking the entire cache, which may be slow.
This commit is contained in:
Andreas Kling 2019-11-05 19:35:12 +01:00
parent 3de3daf765
commit 59ed235c85
7 changed files with 59 additions and 18 deletions
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9
Kernel/FileSystem/DiskBackedFileSystem.h
View file

@ -21,14 +21,15 @@ public:
protected:
explicit DiskBackedFS(NonnullRefPtr<DiskDevice>&&);
bool read_block(unsigned index, u8* buffer) const;
bool read_blocks(unsigned index, unsigned count, u8* buffer) const;
bool read_block(unsigned index, u8* buffer, FileDescription* = nullptr) const;
bool read_blocks(unsigned index, unsigned count, u8* buffer, FileDescription* = nullptr) const;
bool write_block(unsigned index, const u8*);
bool write_blocks(unsigned index, unsigned count, const u8*);
bool write_block(unsigned index, const u8*, FileDescription* = nullptr);
bool write_blocks(unsigned index, unsigned count, const u8*, FileDescription* = nullptr);
private:
DiskCache& cache() const;
void flush_specific_block_if_needed(unsigned index);
NonnullRefPtr<DiskDevice> m_device;
mutable OwnPtr<DiskCache> m_cache;