From c8961a6cbde04603398d1db92b8a26147453f3a7 Mon Sep 17 00:00:00 2001
From: Ayush Ranjan <ayushranjan@google.com>
Date: Fri, 9 Aug 2019 13:07:06 -0700
Subject: ext: Move to pkg/sentry/fsimpl.

fsimpl is the keeper of all filesystem implementations in VFS2.

PiperOrigin-RevId: 262617869
---
 pkg/sentry/fsimpl/ext/symlink.go | 111 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 111 insertions(+)
 create mode 100644 pkg/sentry/fsimpl/ext/symlink.go

(limited to 'pkg/sentry/fsimpl/ext/symlink.go')

diff --git a/pkg/sentry/fsimpl/ext/symlink.go b/pkg/sentry/fsimpl/ext/symlink.go
new file mode 100644
index 000000000..e06548a98
--- /dev/null
+++ b/pkg/sentry/fsimpl/ext/symlink.go
@@ -0,0 +1,111 @@
+// 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 ext
+
+import (
+	"gvisor.dev/gvisor/pkg/sentry/context"
+	"gvisor.dev/gvisor/pkg/sentry/memmap"
+	"gvisor.dev/gvisor/pkg/sentry/usermem"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/syserror"
+)
+
+// symlink represents a symlink inode.
+type symlink struct {
+	inode  inode
+	target string // immutable
+}
+
+// newSymlink is the symlink constructor. It reads out the symlink target from
+// the inode (however it might have been stored).
+func newSymlink(inode inode) (*symlink, error) {
+	var file *symlink
+	var link []byte
+
+	// If the symlink target is lesser than 60 bytes, its stores in inode.Data().
+	// Otherwise either extents or block maps will be used to store the link.
+	size := inode.diskInode.Size()
+	if size < 60 {
+		link = inode.diskInode.Data()[:size]
+	} else {
+		// Create a regular file out of this inode and read out the target.
+		regFile, err := newRegularFile(inode)
+		if err != nil {
+			return nil, err
+		}
+
+		link = make([]byte, size)
+		if n, err := regFile.impl.ReadAt(link, 0); uint64(n) < size {
+			return nil, err
+		}
+	}
+
+	file = &symlink{inode: inode, target: string(link)}
+	file.inode.impl = file
+	return file, nil
+}
+
+func (in *inode) isSymlink() bool {
+	_, ok := in.impl.(*symlink)
+	return ok
+}
+
+// symlinkFD represents a symlink file description and implements implements
+// vfs.FileDescriptionImpl. which may only be used if open options contains
+// O_PATH. For this reason most of the functions return EBADF.
+type symlinkFD struct {
+	fileDescription
+}
+
+// Compiles only if symlinkFD implements vfs.FileDescriptionImpl.
+var _ vfs.FileDescriptionImpl = (*symlinkFD)(nil)
+
+// Release implements vfs.FileDescriptionImpl.Release.
+func (fd *symlinkFD) Release() {}
+
+// PRead implements vfs.FileDescriptionImpl.PRead.
+func (fd *symlinkFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
+	return 0, syserror.EBADF
+}
+
+// Read implements vfs.FileDescriptionImpl.Read.
+func (fd *symlinkFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
+	return 0, syserror.EBADF
+}
+
+// PWrite implements vfs.FileDescriptionImpl.PWrite.
+func (fd *symlinkFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
+	return 0, syserror.EBADF
+}
+
+// Write implements vfs.FileDescriptionImpl.Write.
+func (fd *symlinkFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
+	return 0, syserror.EBADF
+}
+
+// IterDirents implements vfs.FileDescriptionImpl.IterDirents.
+func (fd *symlinkFD) IterDirents(ctx context.Context, cb vfs.IterDirentsCallback) error {
+	return syserror.ENOTDIR
+}
+
+// Seek implements vfs.FileDescriptionImpl.Seek.
+func (fd *symlinkFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
+	return 0, syserror.EBADF
+}
+
+// IterDirents implements vfs.FileDescriptionImpl.IterDirents.
+func (fd *symlinkFD) ConfigureMMap(ctx context.Context, opts memmap.MMapOpts) error {
+	return syserror.EBADF
+}
-- 
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