Downgrade FUSE minor version support and clarify comments

pkg/abi/linux/fuse.go

@@ -151,34 +151,27 @@ type FUSEWriteIn struct {
 }
 
 // FUSE_INIT flags, consistent with the ones in include/uapi/linux/fuse.h.
+// Our taget version is 7.23 but we have few implemented in advance.
 const (
-	FUSE_ASYNC_READ          = 1 << 0
-	FUSE_POSIX_LOCKS         = 1 << 1
-	FUSE_FILE_OPS            = 1 << 2
-	FUSE_ATOMIC_O_TRUNC      = 1 << 3
-	FUSE_EXPORT_SUPPORT      = 1 << 4
-	FUSE_BIG_WRITES          = 1 << 5
-	FUSE_DONT_MASK           = 1 << 6
-	FUSE_SPLICE_WRITE        = 1 << 7
-	FUSE_SPLICE_MOVE         = 1 << 8
-	FUSE_SPLICE_READ         = 1 << 9
-	FUSE_FLOCK_LOCKS         = 1 << 10
-	FUSE_HAS_IOCTL_DIR       = 1 << 11
-	FUSE_AUTO_INVAL_DATA     = 1 << 12
-	FUSE_DO_READDIRPLUS      = 1 << 13
-	FUSE_READDIRPLUS_AUTO    = 1 << 14
-	FUSE_ASYNC_DIO           = 1 << 15
-	FUSE_WRITEBACK_CACHE     = 1 << 16
-	FUSE_NO_OPEN_SUPPORT     = 1 << 17
-	FUSE_PARALLEL_DIROPS     = 1 << 18
-	FUSE_HANDLE_KILLPRIV     = 1 << 19
-	FUSE_POSIX_ACL           = 1 << 20
-	FUSE_ABORT_ERROR         = 1 << 21
-	FUSE_MAX_PAGES           = 1 << 22
-	FUSE_CACHE_SYMLINKS      = 1 << 23
-	FUSE_NO_OPENDIR_SUPPORT  = 1 << 24
-	FUSE_EXPLICIT_INVAL_DATA = 1 << 25
-	FUSE_MAP_ALIGNMENT       = 1 << 26
+	FUSE_ASYNC_READ       = 1 << 0
+	FUSE_POSIX_LOCKS      = 1 << 1
+	FUSE_FILE_OPS         = 1 << 2
+	FUSE_ATOMIC_O_TRUNC   = 1 << 3
+	FUSE_EXPORT_SUPPORT   = 1 << 4
+	FUSE_BIG_WRITES       = 1 << 5
+	FUSE_DONT_MASK        = 1 << 6
+	FUSE_SPLICE_WRITE     = 1 << 7
+	FUSE_SPLICE_MOVE      = 1 << 8
+	FUSE_SPLICE_READ      = 1 << 9
+	FUSE_FLOCK_LOCKS      = 1 << 10
+	FUSE_HAS_IOCTL_DIR    = 1 << 11
+	FUSE_AUTO_INVAL_DATA  = 1 << 12
+	FUSE_DO_READDIRPLUS   = 1 << 13
+	FUSE_READDIRPLUS_AUTO = 1 << 14
+	FUSE_ASYNC_DIO        = 1 << 15
+	FUSE_WRITEBACK_CACHE  = 1 << 16
+	FUSE_NO_OPEN_SUPPORT  = 1 << 17
+	FUSE_MAX_PAGES        = 1 << 22 // From FUSE 7.28
 )
 
 // currently supported FUSE protocol version numbers.
@@ -214,7 +207,7 @@ type FUSEInitIn struct {
 }
 
 // FUSEInitOut is the reply sent by the daemon to the kernel
-// for FUSEInitIn.
+// for FUSEInitIn. We target FUSE 7.23; this struct supports 7.28.
 //
 // +marshal
 type FUSEInitOut struct {
@@ -255,9 +248,7 @@ type FUSEInitOut struct {
 	// if the value from daemon is too large.
 	MaxPages uint16
 
-	// MapAlignment is an unknown field and not used by this package at this moment.
-	// Use as a placeholder to be consistent with the FUSE protocol.
-	MapAlignment uint16
+	_ uint16
 
 	_ [8]uint32
 }

pkg/sentry/fsimpl/fuse/connection.go

@@ -86,16 +86,22 @@ type connection struct {
 	// attributeVersion is the version of connection's attributes.
 	attributeVersion uint64
 
+	// We target FUSE 7.23.
 	// The following FUSE_INIT flags are currently unsupported by this implementation:
 	// - FUSE_EXPORT_SUPPORT
-	// - FUSE_HANDLE_KILLPRIV
 	// - FUSE_POSIX_LOCKS: requires POSIX locks
 	// - FUSE_FLOCK_LOCKS: requires POSIX locks
 	// - FUSE_AUTO_INVAL_DATA: requires page caching eviction
-	// - FUSE_EXPLICIT_INVAL_DATA: requires page caching eviction
 	// - FUSE_DO_READDIRPLUS/FUSE_READDIRPLUS_AUTO: requires FUSE_READDIRPLUS implementation
 	// - FUSE_ASYNC_DIO
-	// - FUSE_POSIX_ACL: affects defaultPermissions, posixACL, xattr handler
+	// - FUSE_PARALLEL_DIROPS (7.25)
+	// - FUSE_HANDLE_KILLPRIV (7.26)
+	// - FUSE_POSIX_ACL: affects defaultPermissions, posixACL, xattr handler (7.26)
+	// - FUSE_ABORT_ERROR (7.27)
+	// - FUSE_CACHE_SYMLINKS (7.28)
+	// - FUSE_NO_OPENDIR_SUPPORT (7.29)
+	// - FUSE_EXPLICIT_INVAL_DATA: requires page caching eviction (7.30)
+	// - FUSE_MAP_ALIGNMENT (7.31)
 
 	// initialized after receiving FUSE_INIT reply.
 	// Until it's set, suspend sending FUSE requests.
@@ -182,19 +188,11 @@ type connection struct {
 	// Negotiated and only set in INIT.
 	asyncRead bool
 
-	// abortErr is true if kernel need to return an unique read error after abort.
-	// Negotiated and only set in INIT.
-	abortErr bool
-
 	// writebackCache is true for write-back cache policy,
 	// false for write-through policy.
 	// Negotiated and only set in INIT.
 	writebackCache bool
 
-	// cacheSymlinks if filesystem needs to cache READLINK responses in page cache.
-	// Negotiated and only set in INIT.
-	cacheSymlinks bool
-
 	// bigWrites if doing multi-page cached writes.
 	// Negotiated and only set in INIT.
 	bigWrites bool

pkg/sentry/fsimpl/fuse/init.go

@@ -132,8 +132,6 @@ func (conn *connection) initProcessReply(out *linux.FUSEInitOut, hasSysAdminCap
 		conn.bigWrites = out.Flags&linux.FUSE_BIG_WRITES != 0
 		conn.dontMask = out.Flags&linux.FUSE_DONT_MASK != 0
 		conn.writebackCache = out.Flags&linux.FUSE_WRITEBACK_CACHE != 0
-		conn.cacheSymlinks = out.Flags&linux.FUSE_CACHE_SYMLINKS != 0
-		conn.abortErr = out.Flags&linux.FUSE_ABORT_ERROR != 0
 
 		// TODO(gvisor.dev/issue/3195): figure out how to use TimeGran (0 < TimeGran <= fuseMaxTimeGranNs).
 

pkg/sentry/fsimpl/fuse/request_response.go

@@ -65,11 +65,6 @@ func (r *fuseInitRes) UnmarshalBytes(src []byte) {
 		out.MaxPages = uint16(usermem.ByteOrder.Uint16(src[:2]))
 		src = src[2:]
 	}
-	// Introduced in FUSE kernel version 7.31.
-	if len(src) >= 2 {
-		out.MapAlignment = uint16(usermem.ByteOrder.Uint16(src[:2]))
-		src = src[2:]
-	}
 }
 
 // SizeBytes is the size of the payload of the FUSE_INIT response.