// Copyright 2019 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package kernfs

import (
	"fmt"

	"gvisor.dev/gvisor/pkg/abi/linux"
	"gvisor.dev/gvisor/pkg/atomicbitops"
	"gvisor.dev/gvisor/pkg/context"
	"gvisor.dev/gvisor/pkg/errors/linuxerr"
	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
	"gvisor.dev/gvisor/pkg/sentry/vfs"
	"gvisor.dev/gvisor/pkg/usermem"
	"gvisor.dev/gvisor/pkg/waiter"
)

// DataSourceProvider represents a dynamic data source provider for DynamicBytesFile.
type DataSourceProvider interface {
	DataSource(ctx context.Context) (vfs.DynamicBytesSource, error)
}

// DynamicBytesFile implements kernfs.Inode and represents a read-only file
// whose contents are backed by a vfs.DynamicBytesSource. If data additionally
// implements vfs.WritableDynamicBytesSource, the file also supports dispatching
// writes to the implementer, but note that this will not update the source data.
//
// Must be instantiated with NewDynamicBytesFile or initialized with Init
// before first use.
//
// +stateify savable
type DynamicBytesFile struct {
	InodeAttrs
	InodeNoStatFS
	InodeNoopRefCount
	InodeNotAnonymous
	InodeNotDirectory
	InodeNotSymlink
	InodeWatches
	InodeFSOwned

	locks vfs.FileLocks
	// data can additionally implement vfs.WritableDynamicBytesSource to support
	// writes. This field cannot be changed to a different bytes source after
	// Init.
	data vfs.DynamicBytesSource

	// dataSourceProvider is used to get the data source when the file is opened.
	// If it is nil, the data source is fixed to the value in the data field.
	dataSourceProvider DataSourceProvider
}

var _ Inode = (*DynamicBytesFile)(nil)

// Init initializes a dynamic bytes file.
func (f *DynamicBytesFile) Init(ctx context.Context, creds *auth.Credentials, devMajor, devMinor uint32, ino uint64, data vfs.DynamicBytesSource, perm linux.FileMode) {
	if perm&^linux.PermissionsMask != 0 {
		panic(fmt.Sprintf("Only permission mask must be set: %x", perm&linux.PermissionsMask))
	}
	f.InodeAttrs.Init(ctx, creds, devMajor, devMinor, ino, linux.ModeRegular|perm)
	f.data = data
}

// InitWithIDs initializes a dynamic bytes file with the given owner UIDs and GIDs.
func (f *DynamicBytesFile) InitWithIDs(ctx context.Context, uid auth.KUID, gid auth.KGID, devMajor, devMinor uint32, ino uint64, data vfs.DynamicBytesSource, perm linux.FileMode) {
	if perm&^linux.PermissionsMask != 0 {
		panic(fmt.Sprintf("Only permission mask must be set: %x", perm&linux.PermissionsMask))
	}
	f.InodeAttrs.InitWithIDs(ctx, uid, gid, devMajor, devMinor, ino, linux.ModeRegular|perm)
	f.data = data
}

// Open implements Inode.Open.
func (f *DynamicBytesFile) Open(ctx context.Context, rp *vfs.ResolvingPath, d *Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
	data, err := f.Data(ctx)
	if err != nil {
		return nil, err
	}

	if src, ok := data.(vfs.PollableDynamicBytesSource); ok {
		if poller := src.GetDynamicBytesPoller(ctx); poller != nil {
			// Pollable fd
			fd := &PollableDynamicBytesFD{}
			if err := fd.Init(rp.Mount(), d, data, &f.locks, opts.Flags, rp.Credentials(), poller); err != nil {
				return nil, err
			}

			return &fd.vfsfd, nil
		}
	}

	// Non-pollable fd
	fd := &DynamicBytesFD{}
	if err := fd.Init(rp.Mount(), d, data, &f.locks, opts.Flags, rp.Credentials()); err != nil {
		return nil, err
	}

	return &fd.vfsfd, nil
}

// SetStat implements Inode.SetStat. By default DynamicBytesFile doesn't allow
// inode attributes to be changed. Override SetStat() making it call
// f.InodeAttrs to allow it.
func (*DynamicBytesFile) SetStat(context.Context, *vfs.Filesystem, *auth.Credentials, vfs.SetStatOptions) error {
	return linuxerr.EPERM
}

// Locks returns the file locks for this file.
func (f *DynamicBytesFile) Locks() *vfs.FileLocks {
	return &f.locks
}

// SetDataSourceProvider sets a DataSourceProvider for the file.
func (f *DynamicBytesFile) SetDataSourceProvider(p DataSourceProvider) {
	f.dataSourceProvider = p
}

// Data returns the underlying data source.
func (f *DynamicBytesFile) Data(ctx context.Context) (vfs.DynamicBytesSource, error) {
	if f.dataSourceProvider != nil {
		return f.dataSourceProvider.DataSource(ctx)
	}
	return f.data, nil
}

// DynamicBytesFD implements vfs.FileDescriptionImpl for an FD backed by a
// DynamicBytesFile.
//
// Must be initialized with Init before first use.
//
// +stateify savable
type DynamicBytesFD struct {
	vfs.FileDescriptionDefaultImpl
	vfs.DynamicBytesFileDescriptionImpl
	vfs.LockFD

	vfsfd vfs.FileDescription
	inode Inode
}

// Init initializes a DynamicBytesFD.
func (fd *DynamicBytesFD) Init(m *vfs.Mount, d *Dentry, data vfs.DynamicBytesSource, locks *vfs.FileLocks, flags uint32, creds *auth.Credentials) error {
	return fd.InitWithImpl(fd, m, d, data, locks, flags, creds)
}

// InitWithImpl initializes a DynamicBytesFD, registering impl as the
// vfs.FileDescriptionImpl. Use it when embedding DynamicBytesFD in another
// file description implementation: pass the outer implementation so that its
// method overrides are honored.
func (fd *DynamicBytesFD) InitWithImpl(impl vfs.FileDescriptionImpl, m *vfs.Mount, d *Dentry, data vfs.DynamicBytesSource, locks *vfs.FileLocks, flags uint32, creds *auth.Credentials) error {
	fd.LockFD.Init(locks)
	if err := fd.vfsfd.Init(impl, flags, creds, m, d.VFSDentry(),
		&vfs.FileDescriptionOptions{
			DenySpliceIn: true,
		},
	); err != nil {
		return err
	}
	fd.inode = d.inode
	fd.DynamicBytesFileDescriptionImpl.Init(&fd.vfsfd, data)
	return nil
}

// VFSFileDescription returns a pointer to the vfs.FileDescription
// representing this object.
func (fd *DynamicBytesFD) VFSFileDescription() *vfs.FileDescription {
	return &fd.vfsfd
}

// Seek implements vfs.FileDescriptionImpl.Seek.
func (fd *DynamicBytesFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
	return fd.DynamicBytesFileDescriptionImpl.Seek(ctx, offset, whence)
}

// Read implements vfs.FileDescriptionImpl.Read.
func (fd *DynamicBytesFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
	return fd.DynamicBytesFileDescriptionImpl.Read(ctx, dst, opts)
}

// PRead implements vfs.FileDescriptionImpl.PRead.
func (fd *DynamicBytesFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
	return fd.DynamicBytesFileDescriptionImpl.PRead(ctx, dst, offset, opts)
}

// Write implements vfs.FileDescriptionImpl.Write.
func (fd *DynamicBytesFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
	return fd.DynamicBytesFileDescriptionImpl.Write(ctx, src, opts)
}

// PWrite implements vfs.FileDescriptionImpl.PWrite.
func (fd *DynamicBytesFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
	return fd.DynamicBytesFileDescriptionImpl.PWrite(ctx, src, offset, opts)
}

// Release implements vfs.FileDescriptionImpl.Release.
func (fd *DynamicBytesFD) Release(context.Context) {}

// Stat implements vfs.FileDescriptionImpl.Stat.
func (fd *DynamicBytesFD) Stat(ctx context.Context, opts vfs.StatOptions) (linux.Statx, error) {
	fs := fd.vfsfd.VirtualDentry().Mount().Filesystem()
	return fd.inode.Stat(ctx, fs, opts)
}

// SetStat implements vfs.FileDescriptionImpl.SetStat.
func (fd *DynamicBytesFD) SetStat(context.Context, vfs.SetStatOptions) error {
	// DynamicBytesFiles are immutable.
	return linuxerr.EPERM
}

// PollableDynamicBytesFD represents a DynamicBytesFD that can be monitored
// for changes using select, poll, or epoll.
//
// +stateify savable
type PollableDynamicBytesFD struct {
	DynamicBytesFD

	poller       *vfs.DynamicBytesPoller
	pollSnapshot atomicbitops.Uint64
}

// Init initializes a PollableDynamicBytesFD.
func (fd *PollableDynamicBytesFD) Init(m *vfs.Mount, d *Dentry, data vfs.DynamicBytesSource, locks *vfs.FileLocks, flags uint32, creds *auth.Credentials, poller *vfs.DynamicBytesPoller) error {
	fd.LockFD.Init(locks)
	if err := fd.vfsfd.Init(fd, flags, creds, m, d.VFSDentry(),
		&vfs.FileDescriptionOptions{DenySpliceIn: true}); err != nil {
		return err
	}
	fd.inode = d.inode
	fd.DynamicBytesFileDescriptionImpl.Init(&fd.vfsfd, data)
	fd.poller = poller
	fd.pollSnapshot.Store(poller.Seq())
	return nil
}

// Epollable implements FileDescriptionImpl.Epollable.
func (fd *PollableDynamicBytesFD) Epollable() bool {
	return true
}

// Readiness implements waiter.Waitable.Readiness.
func (fd *PollableDynamicBytesFD) Readiness(mask waiter.EventMask) waiter.EventMask {
	cur := fd.poller.Seq()
	events := waiter.ReadableEvents | waiter.WritableEvents
	if cur != fd.pollSnapshot.Load() {
		fd.pollSnapshot.Store(cur)
		events = waiter.ReadableEvents | vfs.DynamicBytesPollEvents
	}
	return events & mask
}

// EventRegister implements waiter.Waitable.EventRegister.
func (fd *PollableDynamicBytesFD) EventRegister(e *waiter.Entry) error {
	fd.poller.EventRegister(e)
	return nil
}

// EventUnregister implements waiter.Waitable.EventUnregister.
func (fd *PollableDynamicBytesFD) EventUnregister(e *waiter.Entry) {
	fd.poller.EventUnregister(e)
}
