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moby--moby/pkg/mount/mountinfo_linux.go
Kir Kolyshkin c611f18a7f pkg/mount/mountinfo_linux: parser speed up
The mountinfo parser implemented via `fmt.Sscanf()` is slower than the one
using `strings.Split()` and `strconv.Atoi()`. This rewrite helps to speed it
up to a factor of 8x, here is a result from go bench:

> BenchmarkParsingScanf-4      	     300	  22294112 ns/op
> BenchmarkParsingSplit-4      	    3000	   2780703 ns/op

I tried other approaches, such as using `fmt.Sscanf()` for the first
three (integer) fields and `strings.Split()` for the rest, but it slows
things down considerably:

> BenchmarkParsingMixed-4      	    1000	   8827058 ns/op

Note the old code uses `fmt.Sscanf`, when a linear search for '-' field,
when a split for the last 3 fields. The new code relies on a single
split.

I have also added more comments to aid in future development.

Finally, the test data is fixed to now have white space before the first field.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
2018-04-19 14:49:42 -07:00

132 lines
3.9 KiB
Go

package mount // import "github.com/docker/docker/pkg/mount"
import (
"bufio"
"fmt"
"io"
"os"
"strconv"
"strings"
)
func parseInfoFile(r io.Reader, filter FilterFunc) ([]*Info, error) {
s := bufio.NewScanner(r)
out := []*Info{}
for s.Scan() {
if err := s.Err(); err != nil {
return nil, err
}
/*
36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
(1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11)
(1) mount ID: unique identifier of the mount (may be reused after umount)
(2) parent ID: ID of parent (or of self for the top of the mount tree)
(3) major:minor: value of st_dev for files on filesystem
(4) root: root of the mount within the filesystem
(5) mount point: mount point relative to the process's root
(6) mount options: per mount options
(7) optional fields: zero or more fields of the form "tag[:value]"
(8) separator: marks the end of the optional fields
(9) filesystem type: name of filesystem of the form "type[.subtype]"
(10) mount source: filesystem specific information or "none"
(11) super options: per super block options
*/
text := s.Text()
fields := strings.Split(text, " ")
numFields := len(fields)
if numFields < 10 {
// should be at least 10 fields
return nil, fmt.Errorf("Parsing '%s' failed: not enough fields (%d)", text, numFields)
}
p := &Info{}
// ignore any numbers parsing errors, as there should not be any
p.ID, _ = strconv.Atoi(fields[0])
p.Parent, _ = strconv.Atoi(fields[1])
mm := strings.Split(fields[2], ":")
if len(mm) != 2 {
return nil, fmt.Errorf("Parsing '%s' failed: unexpected minor:major pair %s", text, mm)
}
p.Major, _ = strconv.Atoi(mm[0])
p.Minor, _ = strconv.Atoi(mm[1])
p.Root = fields[3]
p.Mountpoint = fields[4]
p.Opts = fields[5]
var skip, stop bool
if filter != nil {
// filter out entries we're not interested in
skip, stop = filter(p)
if skip {
continue
}
}
// one or more optional fields, when a separator (-)
i := 6
for ; i < numFields && fields[i] != "-"; i++ {
switch i {
case 6:
p.Optional = fields[6]
default:
/* NOTE there might be more optional fields before the such as
fields[7]...fields[N] (where N < sepIndex), although
as of Linux kernel 4.15 the only known ones are
mount propagation flags in fields[6]. The correct
behavior is to ignore any unknown optional fields.
*/
break
}
}
if i == numFields {
return nil, fmt.Errorf("Parsing '%s' failed: missing separator ('-')", text)
}
// There should be 3 fields after the separator...
if i+4 > numFields {
return nil, fmt.Errorf("Parsing '%s' failed: not enough fields after a separator", text)
}
// ... but in Linux <= 3.9 mounting a cifs with spaces in a share name
// (like "//serv/My Documents") _may_ end up having a space in the last field
// of mountinfo (like "unc=//serv/My Documents"). Since kernel 3.10-rc1, cifs
// option unc= is ignored, so a space should not appear. In here we ignore
// those "extra" fields caused by extra spaces.
p.Fstype = fields[i+1]
p.Source = fields[i+2]
p.VfsOpts = fields[i+3]
out = append(out, p)
if stop {
break
}
}
return out, nil
}
// Parse /proc/self/mountinfo because comparing Dev and ino does not work from
// bind mounts
func parseMountTable(filter FilterFunc) ([]*Info, error) {
f, err := os.Open("/proc/self/mountinfo")
if err != nil {
return nil, err
}
defer f.Close()
return parseInfoFile(f, filter)
}
// PidMountInfo collects the mounts for a specific process ID. If the process
// ID is unknown, it is better to use `GetMounts` which will inspect
// "/proc/self/mountinfo" instead.
func PidMountInfo(pid int) ([]*Info, error) {
f, err := os.Open(fmt.Sprintf("/proc/%d/mountinfo", pid))
if err != nil {
return nil, err
}
defer f.Close()
return parseInfoFile(f, nil)
}