Set ownership on symlinks created by build actions during their execution

In commit 410ea5c
"Set ownership on files created by build actions during their execution"
files got correct ownership associated with them. This commit adds the
same feature to symlinks.

One use case is to allow hardlinking symlinks, which requires the owner
of the symlink to be correct.

The following test was performed with Bazel:
```starlark
--- rules.bzl ---
def _impl(ctx):
    file = ctx.actions.declare_file("file")
    symlink = ctx.actions.declare_symlink("symlink")
    args = ctx.actions.args()
    args.add_all([file, symlink])
    ctx.actions.run_shell(
        outputs = [file, symlink],
        command = """
exec 2>&1
set +ex
touch $1
ln -s file $2
ln $2 $2.hardlink
ls -la $(dirname $1)
""",
        arguments = [args],
    )
    return [
        DefaultInfo(files = depset([file, symlink])),
        OutputGroupInfo(
            file = depset([file]),
        ),
    ]

hardlink_a_symlink_rule = rule(
    implementation = _impl,
)

--- BUILD.bazel ---
load(":rules.bzl", "hardlink_a_symlink_rule")

hardlink_a_symlink_rule(name = "hardlink_a_symlink")

filegroup(
    name = "hardlink_a_symlink_file",
    srcs = [":hardlink_a_symlink"],
    output_group = "file",
)
genrule(
    name = "hardlink_input_symlink",
    srcs = [":hardlink_a_symlink", ":hardlink_a_symlink_file"],
    outs = ["symlink.another_hardlink"],
    cmd = """
exec 2>&1
set +ex
cd $$(dirname $(location :hardlink_a_symlink_file))
ln symlink symlink.another_hardlink
ls -la
""",
)

--- Output ---
$ bazel build :hardlink_input_symlink
INFO: From Action file:
total 0
drwxrwxrwx    1 fredrik fredrik 0 Feb  5 21:12 .
drwxrwxrwx    1 fredrik fredrik 0 Feb  5 21:12 ..
-rw-rw-rw-    1 fredrik fredrik 0 Feb  5 21:12 file
lrwxrwxrwx 9999 fredrik fredrik 4 Jan  1  2000 symlink -> file
lrwxrwxrwx 9999 fredrik fredrik 4 Jan  1  2000 symlink.hardlink -> file
INFO: From Executing genrule //:hardlink_input_symlink:
total 0
drwxrwxrwx    1 fredrik fredrik 0 Feb  5 21:12 .
drwxrwxrwx    1 fredrik fredrik 0 Feb  5 21:12 ..
-r-xr-xr-x 9999 root    root    0 Jan  1  2000 file
lrwxrwxrwx 9999 fredrik fredrik 4 Jan  1  2000 symlink -> file
lrwxrwxrwx 9999 fredrik fredrik 4 Jan  1  2000 symlink.another_hardlink -> file
```

References:
https://sourceforge.net/p/fuse/mailman/message/35004606/
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=800179c9b8a1e796e441674776d11cd4c05d61d7
torvalds/linux@800179c

Author: moroten

cmd/bb_worker/main.go

@@ -219,16 +219,16 @@ func main() {
 					normalizer = virtual.CaseInsensitiveComponentNormalizer
 				}
 
+				defaultAttributesSetter := func(requested virtual.AttributesMask, attributes *virtual.Attributes) {
+					// No need to set ownership attributes
+					// on the top-level directory.
+				}
 				symlinkFactory = virtual.NewHandleAllocatingSymlinkFactory(
-					virtual.BaseSymlinkFactory,
+					virtual.NewBaseSymlinkFactory(defaultAttributesSetter),
 					handleAllocator.New())
 				characterDeviceFactory = virtual.NewHandleAllocatingCharacterDeviceFactory(
 					virtual.BaseCharacterDeviceFactory,
 					handleAllocator.New())
-				defaultAttributesSetter := func(requested virtual.AttributesMask, attributes *virtual.Attributes) {
-					// No need to set ownership attributes
-					// on the top-level directory.
-				}
 				virtualBuildDirectory = virtual.NewInMemoryPrepopulatedDirectory(
 					virtual.NewHandleAllocatingFileAllocator(
 						virtual.NewPoolBackedFileAllocator(
@@ -343,6 +343,13 @@ func main() {
 				}
 				runnerClient := runner_pb.NewRunnerClient(runnerConnection)
 
+				defaultAttributesSetter := func(requested virtual.AttributesMask, attributes *virtual.Attributes) {
+					attributes.SetOwnerUserID(runnerConfiguration.BuildDirectoryOwnerUserId)
+					attributes.SetOwnerGroupID(runnerConfiguration.BuildDirectoryOwnerGroupId)
+				}
+				symlinkFactory := virtual.NewHandleAllocatingSymlinkFactory(
+					virtual.NewBaseSymlinkFactory(defaultAttributesSetter),
+					handleAllocator.New())
 				for threadID := uint64(0); threadID < runnerConfiguration.Concurrency; threadID++ {
 					// Per-worker separate writer of the Content
 					// Addressable Storage that batches writes after
@@ -391,10 +398,7 @@ func main() {
 							symlinkFactory,
 							characterDeviceFactory,
 							handleAllocator,
-							/* defaultAttributesSetter = */ func(requested virtual.AttributesMask, attributes *virtual.Attributes) {
-								attributes.SetOwnerUserID(runnerConfiguration.BuildDirectoryOwnerUserId)
-								attributes.SetOwnerGroupID(runnerConfiguration.BuildDirectoryOwnerGroupId)
-							},
+							defaultAttributesSetter,
 							clock.SystemClock,
 						)
 					} else {

pkg/builder/virtual_build_directory.go

@@ -110,6 +110,7 @@ func (d *virtualBuildDirectory) InstallHooks(filePool pool.FilePool, errorLogger
 			),
 			do.handleAllocator,
 		),
+		do.symlinkFactory,
 		errorLogger,
 		do.defaultAttributesSetter,
 		namedAttributesFactory,

pkg/filesystem/virtual/base_symlink_factory.go

@@ -13,19 +13,30 @@ import (
 	"google.golang.org/grpc/status"
 )
 
-type symlinkFactory struct{}
+type symlinkFactory struct {
+	defaultAttributesSetter DefaultAttributesSetter
+}
 
-func (symlinkFactory) LookupSymlink(target []byte) LinkableLeaf {
-	return symlink{target: target}
+func (f *symlinkFactory) LookupSymlink(target []byte) LinkableLeaf {
+	return symlink{
+		defaultAttributesSetter: f.defaultAttributesSetter,
+		target:                  target,
+	}
 }
 
-// BaseSymlinkFactory can be used to create simple immutable symlink nodes.
-var BaseSymlinkFactory SymlinkFactory = symlinkFactory{}
+// NewBaseSymlinkFactory creates a SymlinkFactory that can be used to create
+// simple immutable symlink nodes.
+func NewBaseSymlinkFactory(defaultAttributesSetter DefaultAttributesSetter) SymlinkFactory {
+	return &symlinkFactory{
+		defaultAttributesSetter: defaultAttributesSetter,
+	}
+}
 
 type symlink struct {
 	placeholderFile
 
-	target []byte
+	defaultAttributesSetter DefaultAttributesSetter
+	target                  []byte
 }
 
 func (f symlink) readlinkParser() (path.Parser, error) {
@@ -48,6 +59,7 @@ func (f symlink) readlinkString() (string, error) {
 }
 
 func (f symlink) VirtualGetAttributes(ctx context.Context, requested AttributesMask, attributes *Attributes) {
+	f.defaultAttributesSetter(requested, attributes)
 	attributes.SetChangeID(0)
 	attributes.SetFileType(filesystem.FileTypeSymlink)
 	attributes.SetHasNamedAttributes(false)

pkg/filesystem/virtual/in_memory_prepopulated_directory.go

@@ -25,7 +25,6 @@ type StringMatcher func(s string) bool
 // inMemoryFilesystem contains state that is shared across all
 // inMemoryPrepopulatedDirectory objects that form a single hierarchy.
 type inMemoryFilesystem struct {
-	symlinkFactory          SymlinkFactory
 	statefulHandleAllocator StatefulHandleAllocator
 	initialContentsSorter   Sorter
 	hiddenFilesMatcher      StringMatcher
@@ -44,6 +43,7 @@ type inMemoryFilesystem struct {
 type inMemorySubtree struct {
 	filesystem              *inMemoryFilesystem
 	fileAllocator           FileAllocator
+	symlinkFactory          SymlinkFactory
 	errorLogger             util.ErrorLogger
 	defaultAttributesSetter DefaultAttributesSetter
 	namedAttributesFactory  NamedAttributesFactory
@@ -52,14 +52,14 @@ type inMemorySubtree struct {
 func newInMemorySubtree(fileAllocator FileAllocator, symlinkFactory SymlinkFactory, errorLogger util.ErrorLogger, handleAllocator StatefulHandleAllocator, initialContentsSorter Sorter, hiddenFilesMatcher StringMatcher, clock clock.Clock, normalizer ComponentNormalizer, defaultAttributesSetter DefaultAttributesSetter, namedAttributesFactory NamedAttributesFactory) *inMemorySubtree {
 	return &inMemorySubtree{
 		filesystem: &inMemoryFilesystem{
-			symlinkFactory:          symlinkFactory,
 			statefulHandleAllocator: handleAllocator,
 			initialContentsSorter:   initialContentsSorter,
 			hiddenFilesMatcher:      hiddenFilesMatcher,
 			normalizer:              normalizer,
 			clock:                   clock,
 		},
 		fileAllocator:           fileAllocator,
+		symlinkFactory:          symlinkFactory,
 		errorLogger:             errorLogger,
 		defaultAttributesSetter: defaultAttributesSetter,
 		namedAttributesFactory:  namedAttributesFactory,
@@ -529,13 +529,14 @@ func (i *inMemoryPrepopulatedDirectory) postRemoveChildren(entries *inMemoryDire
 	}
 }
 
-func (i *inMemoryPrepopulatedDirectory) InstallHooks(fileAllocator FileAllocator, errorLogger util.ErrorLogger, defaultAttributesSetter DefaultAttributesSetter, namedAttributesFactory NamedAttributesFactory) {
+func (i *inMemoryPrepopulatedDirectory) InstallHooks(fileAllocator FileAllocator, symlinkFactory SymlinkFactory, errorLogger util.ErrorLogger, defaultAttributesSetter DefaultAttributesSetter, namedAttributesFactory NamedAttributesFactory) {
 	i.lock.Lock()
 	defer i.lock.Unlock()
 
 	i.subtree = &inMemorySubtree{
 		filesystem:              i.subtree.filesystem,
 		fileAllocator:           fileAllocator,
+		symlinkFactory:          symlinkFactory,
 		errorLogger:             errorLogger,
 		defaultAttributesSetter: defaultAttributesSetter,
 		namedAttributesFactory:  namedAttributesFactory,
@@ -1121,7 +1122,7 @@ func (i *inMemoryPrepopulatedDirectory) VirtualSymlink(ctx context.Context, poin
 	if s := contents.virtualMayAttach(normalizedLinkName); s != StatusOK {
 		return nil, ChangeInfo{}, s
 	}
-	child := i.subtree.filesystem.symlinkFactory.LookupSymlink(pointedTo)
+	child := i.subtree.symlinkFactory.LookupSymlink(pointedTo)
 	changeIDBefore := contents.changeID
 	contents.attach(i.subtree, linkName, normalizedLinkName, inMemoryDirectoryChild{}.FromLeaf(child))
 

pkg/filesystem/virtual/in_memory_prepopulated_directory_test.go

@@ -404,9 +404,10 @@ func TestInMemoryPrepopulatedDirectoryInstallHooks(t *testing.T) {
 	defaultAttributesSetter1 := mock.NewMockDefaultAttributesSetter(ctrl)
 	d := virtual.NewInMemoryPrepopulatedDirectory(fileAllocator1, symlinkFactory1, errorLogger1, handleAllocator, sort.Sort, hiddenFilesPatternForTesting.MatchString, clock.SystemClock, virtual.CaseSensitiveComponentNormalizer, defaultAttributesSetter1.Call, virtual.NoNamedAttributesFactory)
 	fileAllocator2 := mock.NewMockFileAllocator(ctrl)
+	symlinkFactory2 := mock.NewMockSymlinkFactory(ctrl)
 	errorLogger2 := mock.NewMockErrorLogger(ctrl)
 	defaultAttributesSetter2 := mock.NewMockDefaultAttributesSetter(ctrl)
-	d.InstallHooks(fileAllocator2, errorLogger2, defaultAttributesSetter2.Call, virtual.NoNamedAttributesFactory)
+	d.InstallHooks(fileAllocator2, symlinkFactory2, errorLogger2, defaultAttributesSetter2.Call, virtual.NoNamedAttributesFactory)
 
 	// Validate that the top-level directory uses both the new file
 	// allocator and error logger.
@@ -424,6 +425,27 @@ func TestInMemoryPrepopulatedDirectoryInstallHooks(t *testing.T) {
 		&attr)
 	require.Equal(t, virtual.StatusErrIO, s)
 
+	// Validate that symlinks uses the new symlink allocator
+	// and error logger as well.
+	symlinkLeaf := mock.NewMockLinkableLeaf(ctrl)
+	symlinkFactory2.EXPECT().LookupSymlink([]byte("target")).Return(symlinkLeaf)
+	symlinkLeaf.EXPECT().VirtualGetAttributes(
+		ctx,
+		virtual.AttributesMaskInodeNumber,
+		gomock.Any(),
+	).Do(func(ctx context.Context, requested virtual.AttributesMask, attributes *virtual.Attributes) {
+		attributes.SetInodeNumber(3)
+	})
+	var out virtual.Attributes
+	actualLeaf, changeInfo, s := d.VirtualSymlink(ctx, []byte("target"), path.MustNewComponent("symlink"), virtual.AttributesMaskInodeNumber, &out)
+	require.Equal(t, virtual.StatusOK, s)
+	require.NotNil(t, actualLeaf)
+	require.Equal(t, virtual.ChangeInfo{
+		Before: 0,
+		After:  1,
+	}, changeInfo)
+	require.Equal(t, (&virtual.Attributes{}).SetInodeNumber(3), &out)
+
 	// Validate that a subdirectory uses the new file allocator
 	// and error logger as well.
 	inMemoryPrepopulatedDirectoryExpectMkdir(ctrl, handleAllocator)

pkg/filesystem/virtual/prepopulated_directory.go

@@ -99,7 +99,7 @@ type PrepopulatedDirectory interface {
 	// This function is identical to BuildDirectory.InstallHooks(),
 	// except that it uses the FUSE specific FileAllocator instead
 	// of FilePool.
-	InstallHooks(fileAllocator FileAllocator, errorLogger util.ErrorLogger, defaultAttributesSetter DefaultAttributesSetter, namedAttributesFactory NamedAttributesFactory)
+	InstallHooks(fileAllocator FileAllocator, symlinkFactory SymlinkFactory, errorLogger util.ErrorLogger, defaultAttributesSetter DefaultAttributesSetter, namedAttributesFactory NamedAttributesFactory)
 	// FilterChildren() can be used to traverse over all of the
 	// InitialContentsFetcher and LinkableLeaf objects stored in this
 	// directory hierarchy. For each of the objects, a callback is