fuse: opt into OpenFile-less and OpenDir-less mode

This means files in the page cache can be served by the kernel without having to
round-trip into userspace for OpenFile and OpenDir requests.

before:
distri build -pkg=gtk+-2  368,58s user 80,63s system 829% cpu 54,134 total
distri build -pkg=gtk+-2  368,65s user 81,73s system 832% cpu 54,088 total
distri build -pkg=gtk+-2  368,43s user 82,23s system 832% cpu 54,113 total

with OpenDir-less:
distri build -pkg=gtk+-2  367,24s user 82,04s system 828% cpu 54,253 total

with OpenFile-less:
distri build -pkg=gtk+-2  359,90s user 72,55s system 845% cpu 51,161 total
distri build -pkg=gtk+-2  359,90s user 72,55s system 845% cpu 51,161 total
distri build -pkg=gtk+-2  361,42s user 72,55s system 831% cpu 52,205 total

related to #59

cmd/distri/internal/fuse/fuse.go

@@ -236,6 +236,9 @@ func Mount(args []string) (join func(context.Context) error, _ error) {
 		},
 		// Opt into caching resolved symlinks in the kernel page cache:
 		EnableSymlinkCaching: true,
+		// Opt into returning -ENOSYS on OpenFile and OpenDir:
+		EnableNoOpenSupport:    true,
+		EnableNoOpendirSupport: true,
 		//DebugLogger: log.New(os.Stderr, "[debug] ", log.LstdFlags),
 	})
 	if err != nil {
@@ -1066,15 +1069,9 @@ func (fs *fuseFS) GetInodeAttributes(ctx context.Context, op *fuseops.GetInodeAt
 }
 
 func (fs *fuseFS) OpenDir(ctx context.Context, op *fuseops.OpenDirOp) error {
-	_, _, err := fs.squashfsInode(op.Inode)
-	if err != nil {
-		log.Println(err)
-		return fuse.EIO
-	}
-
-	//log.Printf("OpenDir(op=%+v, image %d, inode %d)", op, image, squashfsInode)
-	// TODO: open reader
-	return nil // allow opening any directory
+	// Instruct the kernel to not send OpenDir requests for performance:
+	// https://github.com/torvalds/linux/commit/7678ac50615d9c7a491d9861e020e4f5f71b594c
+	return fuse.ENOSYS
 }
 
 /*
@@ -1201,11 +1198,9 @@ func (fs *fuseFS) ReadDir(ctx context.Context, op *fuseops.ReadDirOp) error {
 }
 
 func (fs *fuseFS) OpenFile(ctx context.Context, op *fuseops.OpenFileOp) error {
-	//log.Printf("OpenFile(op=%+v)", op)
-
-	op.KeepPageCache = true // no modifications are happening in immutable images
-
-	return nil // allow opening any file
+	// Instruct the kernel to not send OpenFile requests for performance:
+	// https://github.com/torvalds/linux/commit/7678ac50615d9c7a491d9861e020e4f5f71b594c
+	return fuse.ENOSYS
 }
 
 func (fs *fuseFS) ReadFile(ctx context.Context, op *fuseops.ReadFileOp) error {

go.mod

@@ -7,7 +7,7 @@ require (
 	github.com/google/go-cmp v0.3.0
 	github.com/google/go-github/v27 v27.0.4
 	github.com/google/renameio v0.0.0-20181108174601-76365acd908f
-	github.com/jacobsa/fuse v0.0.0-20200215070453-7c2b5692506e
+	github.com/jacobsa/fuse v0.0.0-20200215073154-2f65426467b1
 	github.com/klauspost/compress v1.9.7 // indirect
 	github.com/klauspost/pgzip v1.2.1
 	github.com/lpar/gzipped v1.1.0

go.sum

@@ -21,8 +21,8 @@ github.com/google/go-querystring v1.0.0 h1:Xkwi/a1rcvNg1PPYe5vI8GbeBY/jrVuDX5ASu
 github.com/google/go-querystring v1.0.0/go.mod h1:odCYkC5MyYFN7vkCjXpyrEuKhc/BUO6wN/zVPAxq5ck=
 github.com/google/renameio v0.0.0-20181108174601-76365acd908f h1:lhDFIjvRqIJDmEHDSeRSiWee4a0oDr0vPpvdFviPcEo=
 github.com/google/renameio v0.0.0-20181108174601-76365acd908f/go.mod h1:KWCgfxg9yswjAJkECMjeO8J8rahYeXnNhOm40UhjYkI=
-github.com/jacobsa/fuse v0.0.0-20200215070453-7c2b5692506e h1:YNGCeJgVJyy55Ax1X9nQFehX3x4s8jgh6xvL22zsAWU=
-github.com/jacobsa/fuse v0.0.0-20200215070453-7c2b5692506e/go.mod h1:9Aml1MG17JVeXrN4D2mtJvYHtHklJH5bESjCKNzVjFU=
+github.com/jacobsa/fuse v0.0.0-20200215073154-2f65426467b1 h1:MG5fuylvlDJtIZGQav3R4d4rKCs9wSRDkZmDARuLbCg=
+github.com/jacobsa/fuse v0.0.0-20200215073154-2f65426467b1/go.mod h1:9Aml1MG17JVeXrN4D2mtJvYHtHklJH5bESjCKNzVjFU=
 github.com/klauspost/compress v1.9.7 h1:hYW1gP94JUmAhBtJ+LNz5My+gBobDxPR1iVuKug26aA=
 github.com/klauspost/compress v1.9.7/go.mod h1:RyIbtBH6LamlWaDj8nUwkbUhJ87Yi3uG0guNDohfE1A=
 github.com/klauspost/pgzip v1.2.1 h1:oIPZROsWuPHpOdMVWLuJZXwgjhrW8r1yEX8UqMyeNHM=

pkgs/go-github.com-jacobsa-fuse/build.textproto

@@ -1,6 +1,6 @@
-source: "distri+gomod://github.com/jacobsa/[email protected]20200215070453-7c2b5692506e"
-hash: "6222d125a9bdcd28b37d55d8e88e63d011270be4b4d600f882b2138b0e76ada5"
-version: "v0.0.0-20200215070453-7c2b5692506e-5"
+source: "distri+gomod://github.com/jacobsa/[email protected]20200215073154-2f65426467b1"
+hash: "09d4f926e458201cd6815c287979c457855200c0c84f66af55dc733cc06c6b61"
+version: "v0.0.0-20200215073154-2f65426467b1-6"
 
 gomodbuilder: {}