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// Copyright 2018 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 linux
import (
"gvisor.dev/gvisor/pkg/errors/linuxerr"
"gvisor.dev/gvisor/pkg/sentry/arch"
"gvisor.dev/gvisor/pkg/sentry/kernel"
)
const (
_SYSLOG_ACTION_READ_ALL = 3
_SYSLOG_ACTION_SIZE_BUFFER = 10
)
// logBufLen is the default syslog buffer size on Linux.
const logBufLen = 1 << 17
// Syslog implements part of Linux syscall syslog.
//
// Only the unprivileged commands are implemented, allowing applications to
// read a fun dmesg.
func Syslog(t *kernel.Task, sysno uintptr, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
command := args[0].Int()
buf := args[1].Pointer()
size := int(args[2].Int())
switch command {
case _SYSLOG_ACTION_READ_ALL:
if size < 0 {
return 0, nil, linuxerr.EINVAL
}
if size > logBufLen {
size = logBufLen
}
log := t.Kernel().Syslog().Log()
if len(log) > size {
log = log[:size]
}
n, err := t.CopyOutBytes(buf, log)
return uintptr(n), nil, err
case _SYSLOG_ACTION_SIZE_BUFFER:
return logBufLen, nil, nil
default:
return 0, nil, linuxerr.ENOSYS
}
}
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