procfs: Migrate seqfile implementations.

Migrates all (except 3) seqfile implementations to the vfs.DynamicBytesSource
interface. There should not be any change in functionality due to this migration
itself.

Please note that the following seqfile implementations have not been migrated:
- /proc/filesystems in proc/filesystems.go
- /proc/[pid]/mountinfo in proc/mounts.go
- /proc/[pid]/mounts in proc/mounts.go
This is because these depend on pending changes in /pkg/senty/vfs.

PiperOrigin-RevId: 263880719

1 files changed, 68 insertions, 0 deletions

diff --git a/pkg/sentry/fsimpl/proc/version.go b/pkg/sentry/fsimpl/proc/version.go
new file mode 100644
index 000000000..e1643d4e0
--- /dev/null
+++ b/pkg/sentry/fsimpl/proc/version.go
@@ -0,0 +1,68 @@
+// Copyright 2019 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 proc
+
+import (
+	"bytes"
+	"fmt"
+
+	"gvisor.dev/gvisor/pkg/sentry/context"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+)
+
+// versionData implements vfs.DynamicBytesSource for /proc/version.
+//
+// +stateify savable
+type versionData struct {
+	// k is the owning Kernel.
+	k *kernel.Kernel
+}
+
+var _ vfs.DynamicBytesSource = (*versionData)(nil)
+
+// Generate implements vfs.DynamicBytesSource.Generate.
+func (v *versionData) Generate(ctx context.Context, buf *bytes.Buffer) error {
+	init := v.k.GlobalInit()
+	if init == nil {
+		// Attempted to read before the init Task is created. This can
+		// only occur during startup, which should never need to read
+		// this file.
+		panic("Attempted to read version before initial Task is available")
+	}
+
+	// /proc/version takes the form:
+	//
+	// "SYSNAME version RELEASE (COMPILE_USER@COMPILE_HOST)
+	// (COMPILER_VERSION) VERSION"
+	//
+	// where:
+	// - SYSNAME, RELEASE, and VERSION are the same as returned by
+	// sys_utsname
+	// - COMPILE_USER is the user that build the kernel
+	// - COMPILE_HOST is the hostname of the machine on which the kernel
+	// was built
+	// - COMPILER_VERSION is the version reported by the building compiler
+	//
+	// Since we don't really want to expose build information to
+	// applications, those fields are omitted.
+	//
+	// FIXME(mpratt): Using Version from the init task SyscallTable
+	// disregards the different version a task may have (e.g., in a uts
+	// namespace).
+	ver := init.Leader().SyscallTable().Version
+	fmt.Fprintf(buf, "%s version %s %s\n", ver.Sysname, ver.Release, ver.Version)
+	return nil
+}