fuse: request explicit control over data cache if filesystem asks for it

This complements commit "fuse: allow filesystems to disable
CAP_AUTO_INVAL_DATA" and teaches go-fuse to request explicit data cache
invalidation mode if fuse.MountOptions.ExplicitDataCacheControl is set.

See https://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse.git/commit/?id=ad2ba64dd489
and https://lwn.net/ml/linux-fsdevel/20190315212556.9315-1-kirr%40nexedi.com/ for rationale and details.

fuse/api.go

@@ -157,12 +157,6 @@ type MountOptions struct {
 
 	// If set, ask kernel not to do automatic data cache invalidation.
 	// The filesystem is fully responsible for invalidating data cache.
-	//
-	// XXX for Linux ExplicitDataCacheControl currently disables data cache
-	// to be automatically invalidated only on file mtime change. If file size
-	// changes, Linux currently unconditionally discards whole cache of the
-	// file. See https://github.com/hanwen/go-fuse/pull/273 for kernel +
-	// go-fuse patches with corresponding fixes.
 	ExplicitDataCacheControl bool
 }
 

fuse/opcode.go

@@ -98,14 +98,13 @@ func doInit(server *Server, req *request) {
 
 	dataCacheMode := input.Flags & CAP_AUTO_INVAL_DATA
 	if server.opts.ExplicitDataCacheControl {
-		// XXX this only disables automatic invalidations on mtime
-		// change, but not on size change.
-		//
-		// TODO explicitly disable invalidations on size change when
-		// kernel has proper support. Details:
-		//
-		//	https://github.com/hanwen/go-fuse/pull/273
+		// we don't want CAP_AUTO_INVAL_DATA even if we cannot go into fully explicit mode
 		dataCacheMode = 0
+
+		explicit := input.Flags & CAP_EXPLICIT_INVAL_DATA
+		if explicit != 0 {
+			dataCacheMode = explicit
+		}
 	}
 	server.kernelSettings.Flags |= dataCacheMode
 

fuse/print.go

@@ -20,31 +20,32 @@ var (
 		READ_LOCKOWNER: "LOCKOWNER",
 	}
 	initFlagNames = map[int64]string{
-		CAP_ASYNC_READ:         "ASYNC_READ",
-		CAP_POSIX_LOCKS:        "POSIX_LOCKS",
-		CAP_FILE_OPS:           "FILE_OPS",
-		CAP_ATOMIC_O_TRUNC:     "ATOMIC_O_TRUNC",
-		CAP_EXPORT_SUPPORT:     "EXPORT_SUPPORT",
-		CAP_BIG_WRITES:         "BIG_WRITES",
-		CAP_DONT_MASK:          "DONT_MASK",
-		CAP_SPLICE_WRITE:       "SPLICE_WRITE",
-		CAP_SPLICE_MOVE:        "SPLICE_MOVE",
-		CAP_SPLICE_READ:        "SPLICE_READ",
-		CAP_FLOCK_LOCKS:        "FLOCK_LOCKS",
-		CAP_IOCTL_DIR:          "IOCTL_DIR",
-		CAP_AUTO_INVAL_DATA:    "AUTO_INVAL_DATA",
-		CAP_READDIRPLUS:        "READDIRPLUS",
-		CAP_READDIRPLUS_AUTO:   "READDIRPLUS_AUTO",
-		CAP_ASYNC_DIO:          "ASYNC_DIO",
-		CAP_WRITEBACK_CACHE:    "WRITEBACK_CACHE",
-		CAP_NO_OPEN_SUPPORT:    "NO_OPEN_SUPPORT",
-		CAP_PARALLEL_DIROPS:    "PARALLEL_DIROPS",
-		CAP_POSIX_ACL:          "POSIX_ACL",
-		CAP_HANDLE_KILLPRIV:    "HANDLE_KILLPRIV",
-		CAP_ABORT_ERROR:        "ABORT_ERROR",
-		CAP_MAX_PAGES:          "MAX_PAGES",
-		CAP_CACHE_SYMLINKS:     "CACHE_SYMLINKS",
-		CAP_NO_OPENDIR_SUPPORT: "NO_OPENDIR_SUPPORT",
+		CAP_ASYNC_READ:          "ASYNC_READ",
+		CAP_POSIX_LOCKS:         "POSIX_LOCKS",
+		CAP_FILE_OPS:            "FILE_OPS",
+		CAP_ATOMIC_O_TRUNC:      "ATOMIC_O_TRUNC",
+		CAP_EXPORT_SUPPORT:      "EXPORT_SUPPORT",
+		CAP_BIG_WRITES:          "BIG_WRITES",
+		CAP_DONT_MASK:           "DONT_MASK",
+		CAP_SPLICE_WRITE:        "SPLICE_WRITE",
+		CAP_SPLICE_MOVE:         "SPLICE_MOVE",
+		CAP_SPLICE_READ:         "SPLICE_READ",
+		CAP_FLOCK_LOCKS:         "FLOCK_LOCKS",
+		CAP_IOCTL_DIR:           "IOCTL_DIR",
+		CAP_AUTO_INVAL_DATA:     "AUTO_INVAL_DATA",
+		CAP_READDIRPLUS:         "READDIRPLUS",
+		CAP_READDIRPLUS_AUTO:    "READDIRPLUS_AUTO",
+		CAP_ASYNC_DIO:           "ASYNC_DIO",
+		CAP_WRITEBACK_CACHE:     "WRITEBACK_CACHE",
+		CAP_NO_OPEN_SUPPORT:     "NO_OPEN_SUPPORT",
+		CAP_PARALLEL_DIROPS:     "PARALLEL_DIROPS",
+		CAP_POSIX_ACL:           "POSIX_ACL",
+		CAP_HANDLE_KILLPRIV:     "HANDLE_KILLPRIV",
+		CAP_ABORT_ERROR:         "ABORT_ERROR",
+		CAP_MAX_PAGES:           "MAX_PAGES",
+		CAP_CACHE_SYMLINKS:      "CACHE_SYMLINKS",
+		CAP_NO_OPENDIR_SUPPORT:  "NO_OPENDIR_SUPPORT",
+		CAP_EXPLICIT_INVAL_DATA: "EXPLICIT_INVAL_DATA",
 	}
 	releaseFlagNames = map[int64]string{
 		RELEASE_FLUSH: "FLUSH",

fuse/types.go

@@ -265,31 +265,32 @@ type OpenOut struct {
 
 // To be set in InitIn/InitOut.Flags.
 const (
-	CAP_ASYNC_READ         = (1 << 0)
-	CAP_POSIX_LOCKS        = (1 << 1)
-	CAP_FILE_OPS           = (1 << 2)
-	CAP_ATOMIC_O_TRUNC     = (1 << 3)
-	CAP_EXPORT_SUPPORT     = (1 << 4)
-	CAP_BIG_WRITES         = (1 << 5)
-	CAP_DONT_MASK          = (1 << 6)
-	CAP_SPLICE_WRITE       = (1 << 7)
-	CAP_SPLICE_MOVE        = (1 << 8)
-	CAP_SPLICE_READ        = (1 << 9)
-	CAP_FLOCK_LOCKS        = (1 << 10)
-	CAP_IOCTL_DIR          = (1 << 11)
-	CAP_AUTO_INVAL_DATA    = (1 << 12)
-	CAP_READDIRPLUS        = (1 << 13)
-	CAP_READDIRPLUS_AUTO   = (1 << 14)
-	CAP_ASYNC_DIO          = (1 << 15)
-	CAP_WRITEBACK_CACHE    = (1 << 16)
-	CAP_NO_OPEN_SUPPORT    = (1 << 17)
-	CAP_PARALLEL_DIROPS    = (1 << 18)
-	CAP_HANDLE_KILLPRIV    = (1 << 19)
-	CAP_POSIX_ACL          = (1 << 20)
-	CAP_ABORT_ERROR        = (1 << 21)
-	CAP_MAX_PAGES          = (1 << 22)
-	CAP_CACHE_SYMLINKS     = (1 << 23)
-	CAP_NO_OPENDIR_SUPPORT = (1 << 24)
+	CAP_ASYNC_READ          = (1 << 0)
+	CAP_POSIX_LOCKS         = (1 << 1)
+	CAP_FILE_OPS            = (1 << 2)
+	CAP_ATOMIC_O_TRUNC      = (1 << 3)
+	CAP_EXPORT_SUPPORT      = (1 << 4)
+	CAP_BIG_WRITES          = (1 << 5)
+	CAP_DONT_MASK           = (1 << 6)
+	CAP_SPLICE_WRITE        = (1 << 7)
+	CAP_SPLICE_MOVE         = (1 << 8)
+	CAP_SPLICE_READ         = (1 << 9)
+	CAP_FLOCK_LOCKS         = (1 << 10)
+	CAP_IOCTL_DIR           = (1 << 11)
+	CAP_AUTO_INVAL_DATA     = (1 << 12)
+	CAP_READDIRPLUS         = (1 << 13)
+	CAP_READDIRPLUS_AUTO    = (1 << 14)
+	CAP_ASYNC_DIO           = (1 << 15)
+	CAP_WRITEBACK_CACHE     = (1 << 16)
+	CAP_NO_OPEN_SUPPORT     = (1 << 17)
+	CAP_PARALLEL_DIROPS     = (1 << 18)
+	CAP_HANDLE_KILLPRIV     = (1 << 19)
+	CAP_POSIX_ACL           = (1 << 20)
+	CAP_ABORT_ERROR         = (1 << 21)
+	CAP_MAX_PAGES           = (1 << 22)
+	CAP_CACHE_SYMLINKS      = (1 << 23)
+	CAP_NO_OPENDIR_SUPPORT  = (1 << 24)
+	CAP_EXPLICIT_INVAL_DATA = (1 << 25)
 )
 
 type InitIn struct {