Add basic plumbing for splice and stub implementation.

This does not actually implement an efficient splice or sendfile. Rather, it
adds a generic plumbing to the file internals so that this can be added. All
file implementations use the stub fileutil.NoSplice implementation, which
causes sendfile and splice to fall back to an internal copy.

A basic splice system call interface is added, along with a test.

PiperOrigin-RevId: 249335960
Change-Id: Ic5568be2af0a505c19e7aec66d5af2480ab0939b

8 files changed, 21 insertions, 11 deletions

diff --git a/pkg/sentry/fs/proc/exec_args.go b/pkg/sentry/fs/proc/exec_args.go
index d49dad685..cb28f6bc3 100644
--- a/pkg/sentry/fs/proc/exec_args.go
+++ b/pkg/sentry/fs/proc/exec_args.go
@@ -77,16 +77,17 @@ func (i *execArgInode) GetFile(ctx context.Context, dirent *fs.Dirent, flags fs.
 
 // +stateify savable
 type execArgFile struct {
-	waiter.AlwaysReady              `state:"nosave"`
 	fsutil.FileGenericSeek          `state:"nosave"`
 	fsutil.FileNoIoctl              `state:"nosave"`
 	fsutil.FileNoMMap               `state:"nosave"`
+	fsutil.FileNoSplice             `state:"nosave"`
 	fsutil.FileNotDirReaddir        `state:"nosave"`
 	fsutil.FileNoopRelease          `state:"nosave"`
 	fsutil.FileNoopFlush            `state:"nosave"`
 	fsutil.FileNoopFsync            `state:"nosave"`
 	fsutil.FileNoopWrite            `state:"nosave"`
 	fsutil.FileUseInodeUnstableAttr `state:"nosave"`
+	waiter.AlwaysReady              `state:"nosave"`
 
 	// arg is the type of exec argument this file contains.
 	arg execArgType
diff --git a/pkg/sentry/fs/proc/rpcinet_proc.go b/pkg/sentry/fs/proc/rpcinet_proc.go
index db53686f6..e36c0bfa6 100644
--- a/pkg/sentry/fs/proc/rpcinet_proc.go
+++ b/pkg/sentry/fs/proc/rpcinet_proc.go
@@ -60,15 +60,16 @@ func (i *rpcInetInode) GetFile(ctx context.Context, dirent *fs.Dirent, flags fs.
 
 // rpcInetFile implements fs.FileOperations as RPCs.
 type rpcInetFile struct {
-	waiter.AlwaysReady              `state:"nosave"`
 	fsutil.FileGenericSeek          `state:"nosave"`
 	fsutil.FileNoIoctl              `state:"nosave"`
 	fsutil.FileNoMMap               `state:"nosave"`
+	fsutil.FileNoSplice             `state:"nosave"`
 	fsutil.FileNoopFlush            `state:"nosave"`
 	fsutil.FileNoopFsync            `state:"nosave"`
 	fsutil.FileNoopRelease          `state:"nosave"`
 	fsutil.FileNotDirReaddir        `state:"nosave"`
 	fsutil.FileUseInodeUnstableAttr `state:"nosave"`
+	waiter.AlwaysReady              `state:"nosave"`
 
 	inode *rpcInetInode
 }
diff --git a/pkg/sentry/fs/proc/seqfile/seqfile.go b/pkg/sentry/fs/proc/seqfile/seqfile.go
index 6b0ae9e60..8364d86ed 100644
--- a/pkg/sentry/fs/proc/seqfile/seqfile.go
+++ b/pkg/sentry/fs/proc/seqfile/seqfile.go
@@ -187,6 +187,7 @@ type seqFileOperations struct {
 	fsutil.FileGenericSeek          `state:"nosave"`
 	fsutil.FileNoIoctl              `state:"nosave"`
 	fsutil.FileNoMMap               `state:"nosave"`
+	fsutil.FileNoSplice             `state:"nosave"`
 	fsutil.FileNoopFlush            `state:"nosave"`
 	fsutil.FileNoopFsync            `state:"nosave"`
 	fsutil.FileNoopRelease          `state:"nosave"`
diff --git a/pkg/sentry/fs/proc/sys.go b/pkg/sentry/fs/proc/sys.go
index b889ed625..59846af4f 100644
--- a/pkg/sentry/fs/proc/sys.go
+++ b/pkg/sentry/fs/proc/sys.go
@@ -134,7 +134,6 @@ var _ fs.InodeOperations = (*hostname)(nil)
 
 // +stateify savable
 type hostnameFile struct {
-	waiter.AlwaysReady              `state:"nosave"`
 	fsutil.FileNoIoctl              `state:"nosave"`
 	fsutil.FileNoMMap               `state:"nosave"`
 	fsutil.FileNoSeek               `state:"nosave"`
@@ -143,7 +142,9 @@ type hostnameFile struct {
 	fsutil.FileNoopRelease          `state:"nosave"`
 	fsutil.FileNotDirReaddir        `state:"nosave"`
 	fsutil.FileNoWrite              `state:"nosave"`
+	fsutil.FileNoSplice             `state:"nosave"`
 	fsutil.FileUseInodeUnstableAttr `state:"nosave"`
+	waiter.AlwaysReady              `state:"nosave"`
 }
 
 // Read implements fs.FileOperations.Read.
diff --git a/pkg/sentry/fs/proc/sys_net.go b/pkg/sentry/fs/proc/sys_net.go
index e49794a48..dbf1a987c 100644
--- a/pkg/sentry/fs/proc/sys_net.go
+++ b/pkg/sentry/fs/proc/sys_net.go
@@ -85,15 +85,16 @@ func (m *tcpMemInode) GetFile(ctx context.Context, dirent *fs.Dirent, flags fs.F
 
 // +stateify savable
 type tcpMemFile struct {
-	waiter.AlwaysReady              `state:"nosave"`
 	fsutil.FileGenericSeek          `state:"nosave"`
 	fsutil.FileNoIoctl              `state:"nosave"`
 	fsutil.FileNoMMap               `state:"nosave"`
+	fsutil.FileNoSplice             `state:"nosave"`
 	fsutil.FileNoopRelease          `state:"nosave"`
 	fsutil.FileNoopFlush            `state:"nosave"`
 	fsutil.FileNoopFsync            `state:"nosave"`
 	fsutil.FileNotDirReaddir        `state:"nosave"`
 	fsutil.FileUseInodeUnstableAttr `state:"nosave"`
+	waiter.AlwaysReady              `state:"nosave"`
 
 	tcpMemInode *tcpMemInode
 }
@@ -198,15 +199,16 @@ func (s *tcpSack) GetFile(ctx context.Context, dirent *fs.Dirent, flags fs.FileF
 
 // +stateify savable
 type tcpSackFile struct {
-	waiter.AlwaysReady              `state:"nosave"`
 	fsutil.FileGenericSeek          `state:"nosave"`
 	fsutil.FileNoIoctl              `state:"nosave"`
 	fsutil.FileNoMMap               `state:"nosave"`
+	fsutil.FileNoSplice             `state:"nosave"`
 	fsutil.FileNoopRelease          `state:"nosave"`
 	fsutil.FileNoopFlush            `state:"nosave"`
 	fsutil.FileNoopFsync            `state:"nosave"`
 	fsutil.FileNotDirReaddir        `state:"nosave"`
 	fsutil.FileUseInodeUnstableAttr `state:"nosave"`
+	waiter.AlwaysReady              `state:"nosave"`
 
 	tcpSack *tcpSack
 
diff --git a/pkg/sentry/fs/proc/task.go b/pkg/sentry/fs/proc/task.go
index 66d76d194..494b195cd 100644
--- a/pkg/sentry/fs/proc/task.go
+++ b/pkg/sentry/fs/proc/task.go
@@ -672,16 +672,17 @@ func (c *comm) GetFile(ctx context.Context, dirent *fs.Dirent, flags fs.FileFlag
 
 // +stateify savable
 type commFile struct {
-	waiter.AlwaysReady              `state:"nosave"`
 	fsutil.FileGenericSeek          `state:"nosave"`
 	fsutil.FileNoIoctl              `state:"nosave"`
 	fsutil.FileNoMMap               `state:"nosave"`
+	fsutil.FileNoSplice             `state:"nosave"`
+	fsutil.FileNoWrite              `state:"nosave"`
 	fsutil.FileNoopFlush            `state:"nosave"`
 	fsutil.FileNoopFsync            `state:"nosave"`
 	fsutil.FileNoopRelease          `state:"nosave"`
 	fsutil.FileNotDirReaddir        `state:"nosave"`
-	fsutil.FileNoWrite              `state:"nosave"`
 	fsutil.FileUseInodeUnstableAttr `state:"nosave"`
+	waiter.AlwaysReady              `state:"nosave"`
 
 	t *kernel.Task
 }
@@ -728,16 +729,17 @@ func (a *auxvec) GetFile(ctx context.Context, dirent *fs.Dirent, flags fs.FileFl
 
 // +stateify savable
 type auxvecFile struct {
-	waiter.AlwaysReady              `state:"nosave"`
 	fsutil.FileGenericSeek          `state:"nosave"`
 	fsutil.FileNoIoctl              `state:"nosave"`
 	fsutil.FileNoMMap               `state:"nosave"`
+	fsutil.FileNoSplice             `state:"nosave"`
+	fsutil.FileNoWrite              `state:"nosave"`
 	fsutil.FileNoopFlush            `state:"nosave"`
 	fsutil.FileNoopFsync            `state:"nosave"`
 	fsutil.FileNoopRelease          `state:"nosave"`
 	fsutil.FileNotDirReaddir        `state:"nosave"`
-	fsutil.FileNoWrite              `state:"nosave"`
 	fsutil.FileUseInodeUnstableAttr `state:"nosave"`
+	waiter.AlwaysReady              `state:"nosave"`
 
 	t *kernel.Task
 }
diff --git a/pkg/sentry/fs/proc/uid_gid_map.go b/pkg/sentry/fs/proc/uid_gid_map.go
index 5df3cee13..a14b1b45f 100644
--- a/pkg/sentry/fs/proc/uid_gid_map.go
+++ b/pkg/sentry/fs/proc/uid_gid_map.go
@@ -85,6 +85,7 @@ type idMapFileOperations struct {
 	fsutil.FileGenericSeek          `state:"nosave"`
 	fsutil.FileNoIoctl              `state:"nosave"`
 	fsutil.FileNoMMap               `state:"nosave"`
+	fsutil.FileNoSplice             `state:"nosave"`
 	fsutil.FileNoopFlush            `state:"nosave"`
 	fsutil.FileNoopFsync            `state:"nosave"`
 	fsutil.FileNoopRelease          `state:"nosave"`
diff --git a/pkg/sentry/fs/proc/uptime.go b/pkg/sentry/fs/proc/uptime.go
index 1ddf9fafa..35c3851e1 100644
--- a/pkg/sentry/fs/proc/uptime.go
+++ b/pkg/sentry/fs/proc/uptime.go
@@ -54,16 +54,17 @@ func (u *uptime) GetFile(ctx context.Context, dirent *fs.Dirent, flags fs.FileFl
 
 // +stateify savable
 type uptimeFile struct {
-	waiter.AlwaysReady              `state:"nosave"`
 	fsutil.FileGenericSeek          `state:"nosave"`
 	fsutil.FileNoIoctl              `state:"nosave"`
 	fsutil.FileNoMMap               `state:"nosave"`
+	fsutil.FileNoSplice             `state:"nosave"`
+	fsutil.FileNoWrite              `state:"nosave"`
 	fsutil.FileNoopFlush            `state:"nosave"`
 	fsutil.FileNoopFsync            `state:"nosave"`
 	fsutil.FileNoopRelease          `state:"nosave"`
 	fsutil.FileNotDirReaddir        `state:"nosave"`
-	fsutil.FileNoWrite              `state:"nosave"`
 	fsutil.FileUseInodeUnstableAttr `state:"nosave"`
+	waiter.AlwaysReady              `state:"nosave"`
 
 	startTime ktime.Time
 }