Merge pull request #29 from kolyshkin/openat2

mountinfo.Mounted: add fast path for Linux using openat2

.ci/Vagrantfile.fedora32

@@ -0,0 +1,31 @@
+# -*- mode: ruby -*-
+# vi: set ft=ruby :
+
+Vagrant.configure("2") do |config|
+# Fedora box is used for testing cgroup v2 support
+  config.vm.box = "fedora/32-cloud-base"
+  config.vm.provider :virtualbox do |v|
+    v.memory = 2048
+    v.cpus = 2
+  end
+  config.vm.provider :libvirt do |v|
+    v.memory = 2048
+    v.cpus = 2
+  end
+  config.vm.provision "shell", inline: <<-SHELL
+    set -e -u -o pipefail
+    # Work around dnf mirror failures by retrying a few times
+    for i in $(seq 0 2); do
+      sleep $i
+      cat << EOF | dnf -y shell && break
+config exclude kernel,kernel-core
+config install_weak_deps false
+update
+install make golang-go libseccomp-devel git-core
+ts run
+EOF
+    done
+    dnf clean all
+
+  SHELL
+end

.ci/install-vagrant.sh

@@ -0,0 +1,20 @@
+#!/bin/bash
+set -eux -o pipefail
+VAGRANT_VERSION="2.2.10"
+
+# Based on code from https://github.com/opencontainers/runc
+DEB="vagrant_${VAGRANT_VERSION}_$(uname -m).deb"
+wget "https://releases.hashicorp.com/vagrant/${VAGRANT_VERSION}/$DEB"
+apt-get update
+apt-get install -q -y \
+	bridge-utils \
+	dnsmasq-base \
+	ebtables \
+	libvirt-bin \
+	libvirt-dev \
+	qemu-kvm \
+	qemu-utils \
+	ruby-dev \
+	./"$DEB"
+rm -f "$DEB"
+vagrant plugin install vagrant-libvirt

.github/workflows/test.yml

@@ -4,7 +4,7 @@ jobs:
   test:
     strategy:
       matrix:
-        go-version: [1.13.x, 1.14.x]
+        go-version: [1.14.x, 1.15.x]
         platform: [ubuntu-latest, windows-latest]
     runs-on: ${{ matrix.platform }}
     steps:

.travis.yml

@@ -0,0 +1,15 @@
+dist: bionic
+os: linux
+language: minimal
+cache:
+  directories:
+  - /home/travis/.vagrant.d/boxes
+jobs:
+  include:
+    - name: "Fedora 32"
+      before_install:
+        - sudo .ci/install-vagrant.sh
+        - ln -sf .ci/Vagrantfile.fedora32 Vagrantfile
+        - sudo vagrant up && sudo mkdir -p /root/.ssh && sudo sh -c "vagrant ssh-config >> /root/.ssh/config"
+      script:
+        - sudo ssh default -t 'cd /vagrant && sudo make'

mountinfo/doc.go

@@ -14,9 +14,8 @@
 // parse filters while reading mountinfo. A filter can skip some entries, or stop
 // processing the rest of the file once the needed information is found.
 //
-// For functions that have path as an argument (such as Mounted or various filters),
-// the argument must be
-//  - an absolute path;
+// For mountinfo filters that accept path as an argument, the path must be:
+//  - absolute;
 //  - having all symlinks resolved;
 //  - being cleaned.
 //

mountinfo/go.mod

@@ -2,4 +2,4 @@ module github.com/moby/sys/mountinfo
 
 go 1.14
 
-require golang.org/x/sys v0.0.0-20200223170610-d5e6a3e2c0ae
+require golang.org/x/sys v0.0.0-20200909081042-eff7692f9009

mountinfo/go.sum

@@ -1,2 +1,2 @@
-golang.org/x/sys v0.0.0-20200223170610-d5e6a3e2c0ae h1:/WDfKMnPU+m5M4xB+6x4kaepxRw6jWvR5iDRdvjHgy8=
-golang.org/x/sys v0.0.0-20200223170610-d5e6a3e2c0ae/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20200909081042-eff7692f9009 h1:W0lCpv29Hv0UaM1LXb9QlBHLNP8UFfcKjblhVCWftOM=
+golang.org/x/sys v0.0.0-20200909081042-eff7692f9009/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=

mountinfo/mounted_linux.go

@@ -0,0 +1,58 @@
+package mountinfo
+
+import (
+	"os"
+	"path/filepath"
+
+	"golang.org/x/sys/unix"
+)
+
+// mountedByOpenat2 is a method of detecting a mount that works for all kinds
+// of mounts (incl. bind mounts), but requires a recent (v5.6+) linux kernel.
+func mountedByOpenat2(path string) (bool, error) {
+	dir, last := filepath.Split(path)
+
+	dirfd, err := unix.Openat2(unix.AT_FDCWD, dir, &unix.OpenHow{
+		Flags: unix.O_PATH | unix.O_CLOEXEC,
+	})
+	if err != nil {
+		if err == unix.ENOENT { // not a mount
+			return false, nil
+		}
+		return false, &os.PathError{Op: "openat2", Path: dir, Err: err}
+	}
+	fd, err := unix.Openat2(dirfd, last, &unix.OpenHow{
+		Flags:   unix.O_PATH | unix.O_CLOEXEC | unix.O_NOFOLLOW,
+		Resolve: unix.RESOLVE_NO_XDEV,
+	})
+	_ = unix.Close(dirfd)
+	switch err {
+	case nil: // definitely not a mount
+		_ = unix.Close(fd)
+		return false, nil
+	case unix.EXDEV: // definitely a mount
+		return true, nil
+	case unix.ENOENT: // not a mount
+		return false, nil
+	}
+	// not sure
+	return false, &os.PathError{Op: "openat2", Path: path, Err: err}
+}
+
+func mounted(path string) (bool, error) {
+	// Try a fast path, using openat2() with RESOLVE_NO_XDEV.
+	mounted, err := mountedByOpenat2(path)
+	if err == nil {
+		return mounted, nil
+	}
+	// Another fast path: compare st.st_dev fields.
+	mounted, err = mountedByStat(path)
+	// This does not work for bind mounts, so false negative
+	// is possible, therefore only trust if return is true.
+	if mounted && err == nil {
+		return mounted, nil
+	}
+
+	// Fallback to parsing mountinfo
+	return mountedByMountinfo(path)
+}