syscall: adjust Mount to accomodate stricter FS implementations.

Notably, the "data" argument should be nil if no options are
given, or (at least) the cgroup filesystem will refuse to
mount.

R=bradfitz, rsc
CC=golang-dev
https://golang.org/cl/5147047

src/pkg/syscall/syscall_linux.go

@@ -784,6 +784,16 @@ func ParseDirent(buf []byte, max int, names []string) (consumed int, count int,
 	return origlen - len(buf), count, names
 }
 
+//sys	mount(source string, target string, fstype string, flags uint32, data *byte) (errno int)
+func Mount(source string, target string, fstype string, flags uint32, data string) (errno int) {
+	// Certain file systems get rather angry and EINVAL if you give
+	// them an empty string of data, rather than NULL.
+	if data == "" {
+		return mount(source, target, fstype, flags, nil)
+	}
+	return mount(source, target, fstype, flags, StringBytePtr(data))
+}
+
 // Sendto
 // Recvfrom
 // Socketpair
@@ -834,7 +844,6 @@ func ParseDirent(buf []byte, max int, names []string) (consumed int, count int,
 //sys	Mkdirat(dirfd int, path string, mode uint32) (errno int)
 //sys	Mknod(path string, mode uint32, dev int) (errno int)
 //sys	Mknodat(dirfd int, path string, mode uint32, dev int) (errno int)
-//sys	Mount(source string, target string, fstype string, flags int, data string) (errno int)
 //sys	Nanosleep(time *Timespec, leftover *Timespec) (errno int)
 //sys	Pause() (errno int)
 //sys	PivotRoot(newroot string, putold string) (errno int) = SYS_PIVOT_ROOT

src/pkg/syscall/zsyscall_linux_386.go

@@ -89,6 +89,14 @@ func reboot(magic1 uint, magic2 uint, cmd int, arg string) (errno int) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func mount(source string, target string, fstype string, flags uint32, data *byte) (errno int) {
+	_, _, e1 := Syscall6(SYS_MOUNT, uintptr(unsafe.Pointer(StringBytePtr(source))), uintptr(unsafe.Pointer(StringBytePtr(target))), uintptr(unsafe.Pointer(StringBytePtr(fstype))), uintptr(flags), uintptr(unsafe.Pointer(data)), 0)
+	errno = int(e1)
+	return
+}
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func Access(path string, mode uint32) (errno int) {
 	_, _, e1 := Syscall(SYS_ACCESS, uintptr(unsafe.Pointer(StringBytePtr(path))), uintptr(mode), 0)
 	errno = int(e1)
@@ -464,14 +472,6 @@ func Mknodat(dirfd int, path string, mode uint32, dev int) (errno int) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Mount(source string, target string, fstype string, flags int, data string) (errno int) {
-	_, _, e1 := Syscall6(SYS_MOUNT, uintptr(unsafe.Pointer(StringBytePtr(source))), uintptr(unsafe.Pointer(StringBytePtr(target))), uintptr(unsafe.Pointer(StringBytePtr(fstype))), uintptr(flags), uintptr(unsafe.Pointer(StringBytePtr(data))), 0)
-	errno = int(e1)
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Nanosleep(time *Timespec, leftover *Timespec) (errno int) {
 	_, _, e1 := Syscall(SYS_NANOSLEEP, uintptr(unsafe.Pointer(time)), uintptr(unsafe.Pointer(leftover)), 0)
 	errno = int(e1)

src/pkg/syscall/zsyscall_linux_amd64.go

@@ -89,6 +89,14 @@ func reboot(magic1 uint, magic2 uint, cmd int, arg string) (errno int) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func mount(source string, target string, fstype string, flags uint32, data *byte) (errno int) {
+	_, _, e1 := Syscall6(SYS_MOUNT, uintptr(unsafe.Pointer(StringBytePtr(source))), uintptr(unsafe.Pointer(StringBytePtr(target))), uintptr(unsafe.Pointer(StringBytePtr(fstype))), uintptr(flags), uintptr(unsafe.Pointer(data)), 0)
+	errno = int(e1)
+	return
+}
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func Access(path string, mode uint32) (errno int) {
 	_, _, e1 := Syscall(SYS_ACCESS, uintptr(unsafe.Pointer(StringBytePtr(path))), uintptr(mode), 0)
 	errno = int(e1)
@@ -464,14 +472,6 @@ func Mknodat(dirfd int, path string, mode uint32, dev int) (errno int) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Mount(source string, target string, fstype string, flags int, data string) (errno int) {
-	_, _, e1 := Syscall6(SYS_MOUNT, uintptr(unsafe.Pointer(StringBytePtr(source))), uintptr(unsafe.Pointer(StringBytePtr(target))), uintptr(unsafe.Pointer(StringBytePtr(fstype))), uintptr(flags), uintptr(unsafe.Pointer(StringBytePtr(data))), 0)
-	errno = int(e1)
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Nanosleep(time *Timespec, leftover *Timespec) (errno int) {
 	_, _, e1 := Syscall(SYS_NANOSLEEP, uintptr(unsafe.Pointer(time)), uintptr(unsafe.Pointer(leftover)), 0)
 	errno = int(e1)

src/pkg/syscall/zsyscall_linux_arm.go

@@ -89,6 +89,14 @@ func reboot(magic1 uint, magic2 uint, cmd int, arg string) (errno int) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func mount(source string, target string, fstype string, flags uint32, data *byte) (errno int) {
+	_, _, e1 := Syscall6(SYS_MOUNT, uintptr(unsafe.Pointer(StringBytePtr(source))), uintptr(unsafe.Pointer(StringBytePtr(target))), uintptr(unsafe.Pointer(StringBytePtr(fstype))), uintptr(flags), uintptr(unsafe.Pointer(data)), 0)
+	errno = int(e1)
+	return
+}
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func Access(path string, mode uint32) (errno int) {
 	_, _, e1 := Syscall(SYS_ACCESS, uintptr(unsafe.Pointer(StringBytePtr(path))), uintptr(mode), 0)
 	errno = int(e1)
@@ -464,14 +472,6 @@ func Mknodat(dirfd int, path string, mode uint32, dev int) (errno int) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Mount(source string, target string, fstype string, flags int, data string) (errno int) {
-	_, _, e1 := Syscall6(SYS_MOUNT, uintptr(unsafe.Pointer(StringBytePtr(source))), uintptr(unsafe.Pointer(StringBytePtr(target))), uintptr(unsafe.Pointer(StringBytePtr(fstype))), uintptr(flags), uintptr(unsafe.Pointer(StringBytePtr(data))), 0)
-	errno = int(e1)
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Nanosleep(time *Timespec, leftover *Timespec) (errno int) {
 	_, _, e1 := Syscall(SYS_NANOSLEEP, uintptr(unsafe.Pointer(time)), uintptr(unsafe.Pointer(leftover)), 0)
 	errno = int(e1)