Don't support fd sync flags by default

It's not yet clear whether these flags should be added to the standard
so disallow use of them by default for the time being. See
WebAssembly/wasi-filesystem#98 for more
details. These changes are also necessary to ensure the rust WASI tests
pass since they assert that path_open returns ENOTSUP when passing
O_DSYNC/O_RSYNC/O_SYNC.

build-scripts/config_common.cmake

@@ -201,6 +201,11 @@ elseif (WAMR_BUILD_LIBC_WASI EQUAL 1)
 else ()
   message ("     Libc WASI disabled")
 endif ()
+if (WAMR_BUILD_ENABLE_LIBC_WASI_SYNC_FLAGS EQUAL 1)
+  message ("     Libc WASI file descriptor sync flags enabled")
+else()
+  message ("     Libc WASI file descriptor sync flags disabled")
+endif()
 if ((WAMR_BUILD_FAST_INTERP EQUAL 1) AND (WAMR_BUILD_INTERP EQUAL 1))
   add_definitions (-DWASM_ENABLE_FAST_INTERP=1)
   message ("     Fast interpreter enabled")

core/iwasm/libraries/libc-wasi/libc_wasi.cmake

@@ -5,6 +5,12 @@ set (LIBC_WASI_DIR ${CMAKE_CURRENT_LIST_DIR})
 
 add_definitions (-DWASM_ENABLE_LIBC_WASI=1)
 
+if (WAMR_BUILD_ENABLE_LIBC_WASI_SYNC_FLAGS EQUAL 1)
+    add_definitions (-DWASM_ENABLE_LIBC_WASI_SYNC_FLAGS=1)
+else()
+    add_definitions (-DWASM_ENABLE_LIBC_WASI_SYNC_FLAGS=0)
+endif()
+
 include_directories(${LIBC_WASI_DIR}/sandboxed-system-primitives/include
                     ${LIBC_WASI_DIR}/sandboxed-system-primitives/src)
 

core/iwasm/libraries/libc-wasi/sandboxed-system-primitives/src/posix.c

@@ -1970,6 +1970,11 @@ wasmtime_ssp_path_open(wasm_exec_env_t exec_env, struct fd_table *curfds,
     // Convert file descriptor flags.
     if ((fs_flags & __WASI_FDFLAG_APPEND) != 0)
         noflags |= O_APPEND;
+    if ((fs_flags & __WASI_FDFLAG_NONBLOCK) != 0)
+        noflags |= O_NONBLOCK;
+    if (write && (noflags & (O_APPEND | O_TRUNC)) == 0)
+        needed_inheriting |= __WASI_RIGHT_FD_SEEK;
+#if WASM_ENABLE_LIBC_WASI_SYNC_FLAGS == 1
     if ((fs_flags & __WASI_FDFLAG_DSYNC) != 0) {
 #ifdef O_DSYNC
         noflags |= O_DSYNC;
@@ -1978,8 +1983,6 @@ wasmtime_ssp_path_open(wasm_exec_env_t exec_env, struct fd_table *curfds,
 #endif
         needed_inheriting |= __WASI_RIGHT_FD_DATASYNC;
     }
-    if ((fs_flags & __WASI_FDFLAG_NONBLOCK) != 0)
-        noflags |= O_NONBLOCK;
     if ((fs_flags & __WASI_FDFLAG_RSYNC) != 0) {
 #ifdef O_RSYNC
         noflags |= O_RSYNC;
@@ -1992,8 +1995,16 @@ wasmtime_ssp_path_open(wasm_exec_env_t exec_env, struct fd_table *curfds,
         noflags |= O_SYNC;
         needed_inheriting |= __WASI_RIGHT_FD_SYNC;
     }
-    if (write && (noflags & (O_APPEND | O_TRUNC)) == 0)
-        needed_inheriting |= __WASI_RIGHT_FD_SEEK;
+#else
+    // It's not clear whether we want to support these flags in the standard
+    // yet: https://github.com/WebAssembly/wasi-filesystem/issues/98 so disable
+    // them by default in the meanwhile.
+    if (((fs_flags & __WASI_FDFLAG_DSYNC) != 0)
+        || ((fs_flags & __WASI_FDFLAG_RSYNC) != 0)
+        || ((fs_flags & __WASI_FDFLAG_SYNC) != 0)) {
+        return __WASI_ENOTSUP;
+    }
+#endif /* end of WASM_ENABLE_LIBC_WASI_SYNC_FLAGS */
 
     struct path_access pa;
     __wasi_errno_t error =

doc/build_wamr.md

@@ -55,6 +55,8 @@ cmake -DWAMR_BUILD_PLATFORM=linux -DWAMR_BUILD_TARGET=ARM
 
 - **WAMR_BUILD_LIBC_WASI**=1/0, build the [WASI](https://github.com/WebAssembly/WASI) libc subset for WASM app, default to enable if not set
 
+- **WAMR_BUILD_LIBC_WASI_ENABLE_SYNC_FLAGS**=1/0, enable support for the file descriptor flags [`FDFLAGS_DSYNC`](https://docs.rs/wasi/latest/wasi/constant.FDFLAGS_DSYNC.html), [`FDFLAGS_RSYNC`](https://docs.rs/wasi/latest/wasi/constant.FDFLAGS_RSYNC.html) and [`FDFLAGS_DSYNC`](https://docs.rs/wasi/latest/wasi/constant.FDFLAGS_DSYNC.html), default to disable if not set. If enabled, support is dependent on the host OS. 
+
 - **WAMR_BUILD_LIBC_UVWASI**=1/0 (Experiment), build the [WASI](https://github.com/WebAssembly/WASI) libc subset for WASM app based on [uvwasi](https://github.com/nodejs/uvwasi) implementation, default to disable if not set
 
 > Note: for platform which doesn't support **WAMR_BUILD_LIBC_WASI**, e.g. Windows, developer can try using **WAMR_BUILD_LIBC_UVWASI**.