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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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33
Kernel/Syscalls/mmap.cpp
View file

@ -190,10 +190,17 @@ ErrorOr<FlatPtr> Process::sys$mmap(Userspace<Syscall::SC_mmap_params const*> use
if (map_stack && (!map_private || !map_anonymous))
return EINVAL;
Memory::VirtualRange requested_range { VirtualAddress { addr }, rounded_size };
if (addr && !(map_fixed || map_fixed_noreplace)) {
// If there's an address but MAP_FIXED wasn't specified, the address is just a hint.
requested_range = { {}, rounded_size };
}
Memory::Region* region = nullptr;
LockRefPtr<OpenFileDescription> description;
LockRefPtr<Memory::AnonymousVMObject> vmobject;
LockRefPtr<Memory::VMObject> vmobject;
u64 used_offset = 0;
if (map_anonymous) {
auto strategy = map_noreserve ? AllocationStrategy::None : AllocationStrategy::Reserve;
@ -206,6 +213,7 @@ ErrorOr<FlatPtr> Process::sys$mmap(Userspace<Syscall::SC_mmap_params const*> use
} else {
if (offset < 0)
return EINVAL;
used_offset = static_cast<u64>(offset);
if (static_cast<size_t>(offset) & ~PAGE_MASK)
return EINVAL;
description = TRY(open_file_description(fd));
@ -220,6 +228,8 @@ ErrorOr<FlatPtr> Process::sys$mmap(Userspace<Syscall::SC_mmap_params const*> use
}
if (description->inode())
TRY(validate_inode_mmap_prot(prot, *description->inode(), map_shared));
vmobject = TRY(description->vmobject_for_mmap(*this, requested_range, used_offset, map_shared));
}
return address_space().with([&](auto& space) -> ErrorOr<FlatPtr> {
@ -227,17 +237,16 @@ ErrorOr<FlatPtr> Process::sys$mmap(Userspace<Syscall::SC_mmap_params const*> use
if (map_fixed)
TRY(space->unmap_mmap_range(VirtualAddress(addr), size));
Memory::VirtualRange requested_range { VirtualAddress { addr }, rounded_size };
if (addr && !(map_fixed || map_fixed_noreplace)) {
// If there's an address but MAP_FIXED wasn't specified, the address is just a hint.
requested_range = { {}, rounded_size };
}
if (map_anonymous) {
region = TRY(space->allocate_region_with_vmobject(map_randomized ? Memory::RandomizeVirtualAddress::Yes : Memory::RandomizeVirtualAddress::No, requested_range.base(), requested_range.size(), alignment, vmobject.release_nonnull(), 0, {}, prot, map_shared));
} else {
region = TRY(description->mmap(*this, *space, requested_range, static_cast<u64>(offset), prot, map_shared));
}
region = TRY(space->allocate_region_with_vmobject(
map_randomized ? Memory::RandomizeVirtualAddress::Yes : Memory::RandomizeVirtualAddress::No,
requested_range.base(),
requested_range.size(),
alignment,
vmobject.release_nonnull(),
used_offset,
{},
prot,
map_shared));
if (!region)
return ENOMEM;