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// Copyright 2020 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 vfs2
import (
"gvisor.dev/gvisor/pkg/sentry/arch"
"gvisor.dev/gvisor/pkg/sentry/kernel"
"gvisor.dev/gvisor/pkg/sentry/syscalls/linux"
"gvisor.dev/gvisor/pkg/sentry/vfs"
"gvisor.dev/gvisor/pkg/syserror"
"gvisor.dev/gvisor/pkg/usermem"
"gvisor.dev/gvisor/pkg/waiter"
)
const (
// EventMaskRead contains events that can be triggered on reads.
EventMaskRead = waiter.EventIn | waiter.EventHUp | waiter.EventErr
)
// Read implements linux syscall read(2). Note that we try to get a buffer that
// is exactly the size requested because some applications like qemu expect
// they can do large reads all at once. Bug for bug. Same for other read
// calls below.
func Read(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
fd := args[0].Int()
addr := args[1].Pointer()
size := args[2].SizeT()
file := t.GetFileVFS2(fd)
if file == nil {
return 0, nil, syserror.EBADF
}
defer file.DecRef()
// Check that the size is legitimate.
si := int(size)
if si < 0 {
return 0, nil, syserror.EINVAL
}
// Get the destination of the read.
dst, err := t.SingleIOSequence(addr, si, usermem.IOOpts{
AddressSpaceActive: true,
})
if err != nil {
return 0, nil, err
}
n, err := read(t, file, dst, vfs.ReadOptions{})
t.IOUsage().AccountReadSyscall(n)
return uintptr(n), nil, linux.HandleIOErrorVFS2(t, n != 0, err, kernel.ERESTARTSYS, "read", file)
}
func read(t *kernel.Task, file *vfs.FileDescription, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
n, err := file.Read(t, dst, opts)
if err != syserror.ErrWouldBlock {
return n, err
}
// Register for notifications.
w, ch := waiter.NewChannelEntry(nil)
file.EventRegister(&w, EventMaskRead)
total := n
for {
// Shorten dst to reflect bytes previously read.
dst = dst.DropFirst(int(n))
// Issue the request and break out if it completes with anything other than
// "would block".
n, err := file.Read(t, dst, opts)
total += n
if err != syserror.ErrWouldBlock {
break
}
if err := t.Block(ch); err != nil {
break
}
}
file.EventUnregister(&w)
return total, err
}
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