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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/AnonymousFile.cpp
View file

@ -1,5 +1,5 @@
/*
* Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2021-2022, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@ -17,12 +17,12 @@ AnonymousFile::AnonymousFile(NonnullLockRefPtr<Memory::AnonymousVMObject> vmobje
AnonymousFile::~AnonymousFile() = default;
ErrorOr<Memory::Region*> AnonymousFile::mmap(Process&, Memory::AddressSpace& address_space, OpenFileDescription&, Memory::VirtualRange const& range, u64 offset, int prot, bool shared)
ErrorOr<NonnullLockRefPtr<Memory::VMObject>> AnonymousFile::vmobject_for_mmap(Process&, Memory::VirtualRange const&, u64& offset, bool)
{
if (offset != 0)
return EINVAL;
return address_space.allocate_region_with_vmobject(range, m_vmobject, offset, {}, prot, shared);
return m_vmobject;
}
ErrorOr<NonnullOwnPtr<KString>> AnonymousFile::pseudo_path(OpenFileDescription const&) const

4
Kernel/FileSystem/AnonymousFile.h
View file

@ -1,5 +1,5 @@
/*
* Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2021-2022, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@ -20,7 +20,7 @@ public:
virtual ~AnonymousFile() override;
virtual ErrorOr<Memory::Region*> mmap(Process&, Memory::AddressSpace&, OpenFileDescription&, Memory::VirtualRange const&, u64 offset, int prot, bool shared) override;
virtual ErrorOr<NonnullLockRefPtr<Memory::VMObject>> vmobject_for_mmap(Process&, Memory::VirtualRange const&, u64& offset, bool shared) override;
private:
virtual StringView class_name() const override { return "AnonymousFile"sv; }

2
Kernel/FileSystem/File.cpp
View file

@ -35,7 +35,7 @@ ErrorOr<void> File::ioctl(OpenFileDescription&, unsigned, Userspace<void*>)
return ENOTTY;
}
ErrorOr<Memory::Region*> File::mmap(Process&, Memory::AddressSpace&, OpenFileDescription&, Memory::VirtualRange const&, u64, int, bool)
ErrorOr<NonnullLockRefPtr<Memory::VMObject>> File::vmobject_for_mmap(Process&, Memory::VirtualRange const&, u64&, bool)
{
return ENODEV;
}

6
Kernel/FileSystem/File.h
View file

@ -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.

13
Kernel/FileSystem/InodeFile.cpp
View file

@ -1,5 +1,5 @@
/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2018-2022, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@ -85,16 +85,11 @@ ErrorOr<void> InodeFile::ioctl(OpenFileDescription& description, unsigned reques
}
}
ErrorOr<Memory::Region*> InodeFile::mmap(Process&, Memory::AddressSpace& address_space, OpenFileDescription& description, Memory::VirtualRange const& range, u64 offset, int prot, bool shared)
ErrorOr<NonnullLockRefPtr<Memory::VMObject>> InodeFile::vmobject_for_mmap(Process&, Memory::VirtualRange const&, u64&, bool shared)
{
// FIXME: If PROT_EXEC, check that the underlying file system isn't mounted noexec.
LockRefPtr<Memory::InodeVMObject> vmobject;
if (shared)
vmobject = TRY(Memory::SharedInodeVMObject::try_create_with_inode(inode()));
else
vmobject = TRY(Memory::PrivateInodeVMObject::try_create_with_inode(inode()));
auto path = TRY(description.pseudo_path());
return address_space.allocate_region_with_vmobject(range, vmobject.release_nonnull(), offset, path->view(), prot, shared);
return TRY(Memory::SharedInodeVMObject::try_create_with_inode(inode()));
return TRY(Memory::PrivateInodeVMObject::try_create_with_inode(inode()));
}
ErrorOr<NonnullOwnPtr<KString>> InodeFile::pseudo_path(OpenFileDescription const&) const

4
Kernel/FileSystem/InodeFile.h
View file

@ -1,5 +1,5 @@
/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2018-2022, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@ -33,7 +33,7 @@ public:
virtual ErrorOr<size_t> read(OpenFileDescription&, u64, UserOrKernelBuffer&, size_t) override;
virtual ErrorOr<size_t> write(OpenFileDescription&, u64, UserOrKernelBuffer const&, size_t) override;
virtual ErrorOr<void> ioctl(OpenFileDescription&, unsigned request, Userspace<void*> arg) override;
virtual ErrorOr<Memory::Region*> mmap(Process&, Memory::AddressSpace&, OpenFileDescription&, Memory::VirtualRange const&, u64 offset, int prot, bool shared) override;
virtual ErrorOr<NonnullLockRefPtr<Memory::VMObject>> vmobject_for_mmap(Process&, Memory::VirtualRange const&, u64& offset, bool shared) override;
virtual ErrorOr<struct stat> stat() const override { return inode().metadata().stat(); }
virtual ErrorOr<NonnullOwnPtr<KString>> pseudo_path(OpenFileDescription const&) const override;

4
Kernel/FileSystem/OpenFileDescription.cpp
View file

@ -374,9 +374,9 @@ InodeMetadata OpenFileDescription::metadata() const
return {};
}
ErrorOr<Memory::Region*> OpenFileDescription::mmap(Process& process, Memory::AddressSpace& address_space, Memory::VirtualRange const& range, u64 offset, int prot, bool shared)
ErrorOr<NonnullLockRefPtr<Memory::VMObject>> OpenFileDescription::vmobject_for_mmap(Process& process, Memory::VirtualRange const& range, u64& offset, bool shared)
{
return m_file->mmap(process, address_space, *this, range, offset, prot, shared);
return m_file->vmobject_for_mmap(process, range, offset, shared);
}
ErrorOr<void> OpenFileDescription::truncate(u64 length)

2
Kernel/FileSystem/OpenFileDescription.h
View file

@ -92,7 +92,7 @@ public:
RefPtr<Custody> custody();
RefPtr<Custody const> custody() const;
ErrorOr<Memory::Region*> mmap(Process&, Memory::AddressSpace&, Memory::VirtualRange const&, u64 offset, int prot, bool shared);
ErrorOr<NonnullLockRefPtr<Memory::VMObject>> vmobject_for_mmap(Process&, Memory::VirtualRange const&, u64& offset, bool shared);
bool is_blocking() const;
void set_blocking(bool b);