tailscale/metrics/fds_linux.go

110 lines
2.7 KiB
Go

// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package metrics
import (
"fmt"
"log"
"syscall"
"unsafe"
"golang.org/x/sys/unix"
)
func currentFDs() int {
fd, err := openProcSelfFD()
if err != nil {
return 0
}
defer syscall.Close(fd)
count := 0
const blockSize = 8 << 10
buf := make([]byte, blockSize) // stack-allocated; doesn't escape
bufp := 0 // starting read position in buf
nbuf := 0 // end valid data in buf
dirent := &syscall.Dirent{}
for {
if bufp >= nbuf {
bufp = 0
nbuf, err = readDirent(fd, buf)
if err != nil {
log.Printf("currentFDs: readDirent: %v", err)
return 0
}
if nbuf <= 0 {
return count
}
}
consumed, name := parseDirEnt(dirent, buf[bufp:nbuf])
bufp += consumed
if len(name) == 0 || string(name) == "." || string(name) == ".." {
continue
}
count++
}
}
func direntNamlen(dirent *syscall.Dirent) int {
const fixedHdr = uint16(unsafe.Offsetof(syscall.Dirent{}.Name))
limit := dirent.Reclen - fixedHdr
const dirNameLen = 256 // sizeof syscall.Dirent.Name
if limit > dirNameLen {
limit = dirNameLen
}
for i := uint16(0); i < limit; i++ {
if dirent.Name[i] == 0 {
return int(i)
}
}
panic("failed to find terminating 0 byte in dirent")
}
func parseDirEnt(dirent *syscall.Dirent, buf []byte) (consumed int, name []byte) {
// golang.org/issue/37269
copy(unsafe.Slice((*byte)(unsafe.Pointer(dirent)), unsafe.Sizeof(syscall.Dirent{})), buf)
if v := unsafe.Offsetof(dirent.Reclen) + unsafe.Sizeof(dirent.Reclen); uintptr(len(buf)) < v {
panic(fmt.Sprintf("buf size of %d smaller than dirent header size %d", len(buf), v))
}
if len(buf) < int(dirent.Reclen) {
panic(fmt.Sprintf("buf size %d < record length %d", len(buf), dirent.Reclen))
}
consumed = int(dirent.Reclen)
if dirent.Ino == 0 { // File absent in directory.
return
}
name = unsafe.Slice((*byte)(unsafe.Pointer(&dirent.Name[0])), direntNamlen(dirent))
return
}
var procSelfFDName = []byte("/proc/self/fd\x00")
func openProcSelfFD() (fd int, err error) {
var dirfd int = unix.AT_FDCWD
for {
r0, _, e1 := syscall.Syscall(unix.SYS_OPENAT, uintptr(dirfd),
uintptr(unsafe.Pointer(&procSelfFDName[0])), 0)
if e1 == 0 {
return int(r0), nil
}
if e1 == syscall.EINTR {
// Since https://golang.org/doc/go1.14#runtime we
// need to loop on EINTR on more places.
continue
}
return 0, syscall.Errno(e1)
}
}
func readDirent(fd int, buf []byte) (n int, err error) {
for {
nbuf, err := syscall.ReadDirent(fd, buf)
if err != syscall.EINTR {
return nbuf, err
}
}
}