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Kernel: Simplify the File memory-mapping API

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Before this change, we had File::mmap() which did all the work of
setting up a VMObject, and then creating a Region in the current
process's address space.

This patch simplifies the interface by removing the region part.
Files now only have to return a suitable VMObject from
vmobject_for_mmap(), and then sys$mmap() itself will take care of
actually mapping it into the address space.

This fixes an issue where we'd try to block on I/O (for inode metadata
lookup) while holding the address space spinlock. It also reduces time
spent holding the address space lock.
This commit is contained in:
Andreas Kling 2022-08-23 18:51:18 +02:00
parent cf16b2c8e6
commit 30861daa93
15 changed files with 49 additions and 58 deletions
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6
Kernel/FileSystem/File.h
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@ -64,11 +64,11 @@ public:
// - Can be overridden in subclasses to implement arbitrary functionality.
// - Subclasses should take care to validate incoming addresses before dereferencing.
//
// mmap()
// vmobject_for_mmap()
//
// - Optional. If unimplemented, mmap() on this File will fail with -ENODEV.
// - Called by mmap() when userspace wants to memory-map this File somewhere.
// - Should create a Region in the Process and return it if successful.
// - Should return a VMObject suitable for mapping into the calling process.
class File
: public AtomicRefCounted<File>
@ -90,7 +90,7 @@ public:
virtual ErrorOr<size_t> read(OpenFileDescription&, u64, UserOrKernelBuffer&, size_t) = 0;
virtual ErrorOr<size_t> write(OpenFileDescription&, u64, UserOrKernelBuffer const&, size_t) = 0;
virtual ErrorOr<void> ioctl(OpenFileDescription&, unsigned request, Userspace<void*> arg);
virtual ErrorOr<Memory::Region*> mmap(Process&, Memory::AddressSpace&, OpenFileDescription&, Memory::VirtualRange const&, u64 offset, int prot, bool shared);
virtual ErrorOr<NonnullLockRefPtr<Memory::VMObject>> vmobject_for_mmap(Process&, Memory::VirtualRange const&, u64& offset, bool shared);
virtual ErrorOr<struct stat> stat() const { return EBADF; }
// Although this might be better described "name" or "description", these terms already have other meanings.