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ladybird/Kernel/FileSystem/MountFile.cpp

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Kernel+LibCore+LibC: Split the mount syscall into multiple syscalls This is a preparation before we can create a usable mechanism to use filesystem-specific mount flags. To keep some compatibility with userland code, LibC and LibCore mount functions are kept being usable, but now instead of doing an "atomic" syscall, they do multiple syscalls to perform the complete procedure of mounting a filesystem. The FileBackedFileSystem IntrusiveList in the VFS code is now changed to be protected by a Mutex, because when we mount a new filesystem, we need to check if a filesystem is already created for a given source_fd so we do a scan for that OpenFileDescription in that list. If we fail to find an already-created filesystem we create a new one and register it in the list if we successfully mounted it. We use a Mutex because we might need to initiate disk access during the filesystem creation, which will take other mutexes in other parts of the kernel, therefore making it not possible to take a spinlock while doing this.
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/*
* Copyright (c) 2022-2023, Liav A. <liavalb@hotmail.co.il>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/StringView.h>
#include <Kernel/API/FileSystem/MountSpecificFlags.h>
#include <Kernel/API/Ioctl.h>
#include <Kernel/API/POSIX/errno.h>
#include <Kernel/API/POSIX/unistd.h>
Kernel: Use FixedStringBuffer for fixed-length strings in syscalls Using the kernel stack is preferable, especially when the examined strings should be limited to a reasonable length. This is a small improvement, because if we don't actually move these strings then we don't need to own heap allocations for them during the syscall handler function scope. In addition to that, some kernel strings are known to be limited, like the hostname string, for these strings we also can use FixedStringBuffer to store and copy to and from these buffers, without using any heap allocations at all.
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#include <Kernel/API/Syscall.h>
Kernel+LibCore+LibC: Split the mount syscall into multiple syscalls This is a preparation before we can create a usable mechanism to use filesystem-specific mount flags. To keep some compatibility with userland code, LibC and LibCore mount functions are kept being usable, but now instead of doing an "atomic" syscall, they do multiple syscalls to perform the complete procedure of mounting a filesystem. The FileBackedFileSystem IntrusiveList in the VFS code is now changed to be protected by a Mutex, because when we mount a new filesystem, we need to check if a filesystem is already created for a given source_fd so we do a scan for that OpenFileDescription in that list. If we fail to find an already-created filesystem we create a new one and register it in the list if we successfully mounted it. We use a Mutex because we might need to initiate disk access during the filesystem creation, which will take other mutexes in other parts of the kernel, therefore making it not possible to take a spinlock while doing this.
2022-12-15 12:42:40 +03:00
#include <Kernel/FileSystem/Inode.h>
#include <Kernel/FileSystem/MountFile.h>
#include <Kernel/FileSystem/OpenFileDescription.h>
#include <Kernel/FileSystem/VirtualFileSystem.h>
#include <Kernel/Library/StdLib.h>
#include <Kernel/Memory/PrivateInodeVMObject.h>
#include <Kernel/Memory/SharedInodeVMObject.h>
Kernel: Use FixedStringBuffer for fixed-length strings in syscalls Using the kernel stack is preferable, especially when the examined strings should be limited to a reasonable length. This is a small improvement, because if we don't actually move these strings then we don't need to own heap allocations for them during the syscall handler function scope. In addition to that, some kernel strings are known to be limited, like the hostname string, for these strings we also can use FixedStringBuffer to store and copy to and from these buffers, without using any heap allocations at all.
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#include <Kernel/Tasks/Process.h>
Kernel+LibCore+LibC: Split the mount syscall into multiple syscalls This is a preparation before we can create a usable mechanism to use filesystem-specific mount flags. To keep some compatibility with userland code, LibC and LibCore mount functions are kept being usable, but now instead of doing an "atomic" syscall, they do multiple syscalls to perform the complete procedure of mounting a filesystem. The FileBackedFileSystem IntrusiveList in the VFS code is now changed to be protected by a Mutex, because when we mount a new filesystem, we need to check if a filesystem is already created for a given source_fd so we do a scan for that OpenFileDescription in that list. If we fail to find an already-created filesystem we create a new one and register it in the list if we successfully mounted it. We use a Mutex because we might need to initiate disk access during the filesystem creation, which will take other mutexes in other parts of the kernel, therefore making it not possible to take a spinlock while doing this.
2022-12-15 12:42:40 +03:00
namespace Kernel {
ErrorOr<NonnullLockRefPtr<MountFile>> MountFile::create(FileSystemInitializer const& file_system_initializer, int flags)
{
// NOTE: We should not open a MountFile if someone wants to either remount or bindmount.
// There's a check for this in the fsopen syscall entry handler, but here we just assert
// to ensure this never happens.
VERIFY(!(flags & MS_BIND));
VERIFY(!(flags & MS_REMOUNT));
auto mount_specific_data_buffer = TRY(KBuffer::try_create_with_size("Mount Specific Data"sv, PAGE_SIZE, Memory::Region::Access::ReadWrite, AllocationStrategy::AllocateNow));
return TRY(adopt_nonnull_lock_ref_or_enomem(new (nothrow) MountFile(file_system_initializer, flags, move(mount_specific_data_buffer))));
}
MountFile::MountFile(FileSystemInitializer const& file_system_initializer, int flags, NonnullOwnPtr<KBuffer> mount_specific_data)
: m_flags(flags)
, m_file_system_initializer(file_system_initializer)
{
m_mount_specific_data.with_exclusive([&](auto& our_mount_specific_data) {
our_mount_specific_data = move(mount_specific_data);
memset(our_mount_specific_data->data(), 0, our_mount_specific_data->size());
});
}
MountFile::~MountFile() = default;
ErrorOr<void> MountFile::ioctl(OpenFileDescription&, unsigned request, Userspace<void*> arg)
{
return m_mount_specific_data.with_exclusive([&](auto& our_mount_specific_data) -> ErrorOr<void> {
switch (request) {
case MOUNT_IOCTL_SET_MOUNT_SPECIFIC_FLAG: {
auto user_mount_specific_data = static_ptr_cast<MountSpecificFlag const*>(arg);
auto mount_specific_data = TRY(copy_typed_from_user(user_mount_specific_data));
if ((mount_specific_data.value_type == MountSpecificFlag::ValueType::SignedInteger || mount_specific_data.value_type == MountSpecificFlag::ValueType::UnsignedInteger) && mount_specific_data.value_length != 8)
return EDOM;
Kernel: Use FixedStringBuffer for fixed-length strings in syscalls Using the kernel stack is preferable, especially when the examined strings should be limited to a reasonable length. This is a small improvement, because if we don't actually move these strings then we don't need to own heap allocations for them during the syscall handler function scope. In addition to that, some kernel strings are known to be limited, like the hostname string, for these strings we also can use FixedStringBuffer to store and copy to and from these buffers, without using any heap allocations at all.
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Syscall::StringArgument user_key_string { reinterpret_cast<const char*>(mount_specific_data.key_string_addr), static_cast<size_t>(mount_specific_data.key_string_length) };
auto key_string = TRY(Process::get_syscall_name_string_fixed_buffer<MOUNT_SPECIFIC_FLAG_KEY_STRING_MAX_LENGTH>(user_key_string));
Kernel+LibCore+LibC: Split the mount syscall into multiple syscalls This is a preparation before we can create a usable mechanism to use filesystem-specific mount flags. To keep some compatibility with userland code, LibC and LibCore mount functions are kept being usable, but now instead of doing an "atomic" syscall, they do multiple syscalls to perform the complete procedure of mounting a filesystem. The FileBackedFileSystem IntrusiveList in the VFS code is now changed to be protected by a Mutex, because when we mount a new filesystem, we need to check if a filesystem is already created for a given source_fd so we do a scan for that OpenFileDescription in that list. If we fail to find an already-created filesystem we create a new one and register it in the list if we successfully mounted it. We use a Mutex because we might need to initiate disk access during the filesystem creation, which will take other mutexes in other parts of the kernel, therefore making it not possible to take a spinlock while doing this.
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if (mount_specific_data.value_type != MountSpecificFlag::ValueType::Boolean && mount_specific_data.value_length == 0)
return EINVAL;
if (mount_specific_data.value_type != MountSpecificFlag::ValueType::Boolean && mount_specific_data.value_addr == nullptr)
return EFAULT;
// NOTE: We put these limits in place because we assume that don't need to handle huge
// amounts of bytes when trying to handle a mount fs-specific flag.
// Anything larger than these constants (which could be changed if needed) is deemed to
// potentially cause OOM condition, and cannot represent any reasonable and "honest" data
// from userspace.
if (mount_specific_data.value_type != MountSpecificFlag::ValueType::ASCIIString && mount_specific_data.value_length > MOUNT_SPECIFIC_FLAG_NON_ASCII_STRING_TYPE_MAX_LENGTH)
return E2BIG;
if (mount_specific_data.value_type == MountSpecificFlag::ValueType::ASCIIString && mount_specific_data.value_length > MOUNT_SPECIFIC_FLAG_ASCII_STRING_TYPE_MAX_LENGTH)
return E2BIG;
// NOTE: We enforce that the passed argument will be either i64 or u64, so it will always be
// exactly 8 bytes. We do that to simplify handling of integers as well as to ensure ABI correctness
// in all possible cases.
switch (mount_specific_data.value_type) {
// NOTE: This is actually considered as simply boolean flag.
case MountSpecificFlag::ValueType::Boolean: {
VERIFY(m_file_system_initializer.handle_mount_boolean_flag);
Userspace<u64*> user_value_addr(reinterpret_cast<FlatPtr>(mount_specific_data.value_addr));
auto value_integer = TRY(copy_typed_from_user(user_value_addr));
if (value_integer != 0 && value_integer != 1)
return EDOM;
bool value = (value_integer == 1) ? true : false;
Kernel: Use FixedStringBuffer for fixed-length strings in syscalls Using the kernel stack is preferable, especially when the examined strings should be limited to a reasonable length. This is a small improvement, because if we don't actually move these strings then we don't need to own heap allocations for them during the syscall handler function scope. In addition to that, some kernel strings are known to be limited, like the hostname string, for these strings we also can use FixedStringBuffer to store and copy to and from these buffers, without using any heap allocations at all.
2023-07-17 19:22:01 +03:00
TRY(m_file_system_initializer.handle_mount_boolean_flag(our_mount_specific_data->bytes(), key_string.representable_view(), value));
Kernel+LibCore+LibC: Split the mount syscall into multiple syscalls This is a preparation before we can create a usable mechanism to use filesystem-specific mount flags. To keep some compatibility with userland code, LibC and LibCore mount functions are kept being usable, but now instead of doing an "atomic" syscall, they do multiple syscalls to perform the complete procedure of mounting a filesystem. The FileBackedFileSystem IntrusiveList in the VFS code is now changed to be protected by a Mutex, because when we mount a new filesystem, we need to check if a filesystem is already created for a given source_fd so we do a scan for that OpenFileDescription in that list. If we fail to find an already-created filesystem we create a new one and register it in the list if we successfully mounted it. We use a Mutex because we might need to initiate disk access during the filesystem creation, which will take other mutexes in other parts of the kernel, therefore making it not possible to take a spinlock while doing this.
2022-12-15 12:42:40 +03:00
return {};
}
case MountSpecificFlag::ValueType::UnsignedInteger: {
VERIFY(m_file_system_initializer.handle_mount_unsigned_integer_flag);
Userspace<u64*> user_value_addr(reinterpret_cast<FlatPtr>(mount_specific_data.value_addr));
auto value_integer = TRY(copy_typed_from_user(user_value_addr));
Kernel: Use FixedStringBuffer for fixed-length strings in syscalls Using the kernel stack is preferable, especially when the examined strings should be limited to a reasonable length. This is a small improvement, because if we don't actually move these strings then we don't need to own heap allocations for them during the syscall handler function scope. In addition to that, some kernel strings are known to be limited, like the hostname string, for these strings we also can use FixedStringBuffer to store and copy to and from these buffers, without using any heap allocations at all.
2023-07-17 19:22:01 +03:00
TRY(m_file_system_initializer.handle_mount_unsigned_integer_flag(our_mount_specific_data->bytes(), key_string.representable_view(), value_integer));
Kernel+LibCore+LibC: Split the mount syscall into multiple syscalls This is a preparation before we can create a usable mechanism to use filesystem-specific mount flags. To keep some compatibility with userland code, LibC and LibCore mount functions are kept being usable, but now instead of doing an "atomic" syscall, they do multiple syscalls to perform the complete procedure of mounting a filesystem. The FileBackedFileSystem IntrusiveList in the VFS code is now changed to be protected by a Mutex, because when we mount a new filesystem, we need to check if a filesystem is already created for a given source_fd so we do a scan for that OpenFileDescription in that list. If we fail to find an already-created filesystem we create a new one and register it in the list if we successfully mounted it. We use a Mutex because we might need to initiate disk access during the filesystem creation, which will take other mutexes in other parts of the kernel, therefore making it not possible to take a spinlock while doing this.
2022-12-15 12:42:40 +03:00
return {};
}
case MountSpecificFlag::ValueType::SignedInteger: {
VERIFY(m_file_system_initializer.handle_mount_signed_integer_flag);
Userspace<i64*> user_value_addr(reinterpret_cast<FlatPtr>(mount_specific_data.value_addr));
auto value_integer = TRY(copy_typed_from_user(user_value_addr));
Kernel: Use FixedStringBuffer for fixed-length strings in syscalls Using the kernel stack is preferable, especially when the examined strings should be limited to a reasonable length. This is a small improvement, because if we don't actually move these strings then we don't need to own heap allocations for them during the syscall handler function scope. In addition to that, some kernel strings are known to be limited, like the hostname string, for these strings we also can use FixedStringBuffer to store and copy to and from these buffers, without using any heap allocations at all.
2023-07-17 19:22:01 +03:00
TRY(m_file_system_initializer.handle_mount_signed_integer_flag(our_mount_specific_data->bytes(), key_string.representable_view(), value_integer));
Kernel+LibCore+LibC: Split the mount syscall into multiple syscalls This is a preparation before we can create a usable mechanism to use filesystem-specific mount flags. To keep some compatibility with userland code, LibC and LibCore mount functions are kept being usable, but now instead of doing an "atomic" syscall, they do multiple syscalls to perform the complete procedure of mounting a filesystem. The FileBackedFileSystem IntrusiveList in the VFS code is now changed to be protected by a Mutex, because when we mount a new filesystem, we need to check if a filesystem is already created for a given source_fd so we do a scan for that OpenFileDescription in that list. If we fail to find an already-created filesystem we create a new one and register it in the list if we successfully mounted it. We use a Mutex because we might need to initiate disk access during the filesystem creation, which will take other mutexes in other parts of the kernel, therefore making it not possible to take a spinlock while doing this.
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return {};
}
case MountSpecificFlag::ValueType::ASCIIString: {
VERIFY(m_file_system_initializer.handle_mount_ascii_string_flag);
auto value_string = TRY(try_copy_kstring_from_user(reinterpret_cast<FlatPtr>(mount_specific_data.value_addr), static_cast<size_t>(mount_specific_data.value_length)));
Kernel: Use FixedStringBuffer for fixed-length strings in syscalls Using the kernel stack is preferable, especially when the examined strings should be limited to a reasonable length. This is a small improvement, because if we don't actually move these strings then we don't need to own heap allocations for them during the syscall handler function scope. In addition to that, some kernel strings are known to be limited, like the hostname string, for these strings we also can use FixedStringBuffer to store and copy to and from these buffers, without using any heap allocations at all.
2023-07-17 19:22:01 +03:00
TRY(m_file_system_initializer.handle_mount_ascii_string_flag(our_mount_specific_data->bytes(), key_string.representable_view(), value_string->view()));
Kernel+LibCore+LibC: Split the mount syscall into multiple syscalls This is a preparation before we can create a usable mechanism to use filesystem-specific mount flags. To keep some compatibility with userland code, LibC and LibCore mount functions are kept being usable, but now instead of doing an "atomic" syscall, they do multiple syscalls to perform the complete procedure of mounting a filesystem. The FileBackedFileSystem IntrusiveList in the VFS code is now changed to be protected by a Mutex, because when we mount a new filesystem, we need to check if a filesystem is already created for a given source_fd so we do a scan for that OpenFileDescription in that list. If we fail to find an already-created filesystem we create a new one and register it in the list if we successfully mounted it. We use a Mutex because we might need to initiate disk access during the filesystem creation, which will take other mutexes in other parts of the kernel, therefore making it not possible to take a spinlock while doing this.
2022-12-15 12:42:40 +03:00
return {};
}
default:
return EINVAL;
}
}
default:
return EINVAL;
}
});
}
ErrorOr<NonnullOwnPtr<KString>> MountFile::pseudo_path(OpenFileDescription const&) const
{
return KString::try_create(":mount-file:"sv);
}
}
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