WasmFS JS API: Implement allocate (#19602)

Also change the type of the __syscall_fallocate to use int64_t instead of uint64_t
so that negative numbers would correctly throw error handling. With uint64_t
setSize() would abort without an error code, since it was interpreting negative
numbers incorrectly. Now, the syscall correctly returns an error code if either
offset or length is negative.

Author: jameshu15869

emcc.py

@@ -2326,6 +2326,7 @@ def phase_linker_setup(options, state, newargs):
         '_wasmfs_read_file',
         '_wasmfs_write_file',
         '_wasmfs_open',
+        '_wasmfs_allocate',
         '_wasmfs_close',
         '_wasmfs_write',
         '_wasmfs_pwrite',

src/library_wasmfs.js

@@ -177,7 +177,9 @@ FS.createPreloadedFile = FS_createPreloadedFile;
 
       return bytesRead;
     },
-    // TODO: allocate
+    allocate: (stream, offset, length) => {
+      return FS.handleError(__wasmfs_allocate(stream.fd, {{{ splitI64('offset') }}}, {{{ splitI64('length') }}}));
+    },
     // TODO: mmap
     // TODO: msync
     // TODO: munmap

system/lib/libc/musl/arch/emscripten/syscall_arch.h

@@ -96,7 +96,7 @@ int __syscall_fchmodat(int dirfd, intptr_t path, int mode, ...);
 int __syscall_faccessat(int dirfd, intptr_t path, int amode, int flags);
 int __syscall_pselect6(int nfds, intptr_t readfds, intptr_t writefds, intptr_t exceptfds, intptr_t timeout, intptr_t sigmaks);
 int __syscall_utimensat(int dirfd, intptr_t path, intptr_t times, int flags);
-int __syscall_fallocate(int fd, int mode, uint64_t off, uint64_t len);
+int __syscall_fallocate(int fd, int mode, int64_t off, int64_t len);
 int __syscall_dup3(int fd, int suggestfd, int flags);
 int __syscall_pipe2(intptr_t fds, int flags);
 int __syscall_recvmmsg(int sockfd, intptr_t msgvec, size_t vlen, int flags, ...);

system/lib/wasmfs/js_api.cpp

@@ -129,6 +129,10 @@ int _wasmfs_open(char* path, int flags, mode_t mode) {
   return __syscall_openat(AT_FDCWD, (intptr_t)path, flags, mode);
 }
 
+int _wasmfs_allocate(int fd, int64_t off, int64_t len) {
+  return __syscall_fallocate(fd, 0, off, len);
+}
+
 int _wasmfs_mknod(char* path, mode_t mode, dev_t dev) {
   return __syscall_mknodat(AT_FDCWD, (intptr_t)path, mode, dev);
 }

system/lib/wasmfs/syscalls.cpp

@@ -1358,7 +1358,7 @@ int __syscall_poll(intptr_t fds_, int nfds, int timeout) {
   return nonzero;
 }
 
-int __syscall_fallocate(int fd, int mode, uint64_t off, uint64_t len) {
+int __syscall_fallocate(int fd, int mode, int64_t off, int64_t len) {
   assert(mode == 0); // TODO, but other modes were never supported in the old FS
 
   auto fileTable = wasmFS.getFileTable().locked();

test/fs/test_fs_js_api.c

@@ -4,6 +4,46 @@
 #include <assert.h>
 #include <fcntl.h>
 
+void test_fs_allocate() {
+    EM_ASM(
+        FS.writeFile("allocatetestfile", 'a=1\nb=2\n');
+    );
+    struct stat allocateStat;
+    stat("allocatetestfile", &allocateStat);
+    assert(allocateStat.st_size == 8);
+
+    EM_ASM(
+        // Allocate more space at the very end.
+        var stream = FS.open("allocatetestfile", "w");
+        FS.allocate(stream, 8, 10);
+    );
+    stat("allocatetestfile", &allocateStat);
+    assert(allocateStat.st_size == 18);
+
+    EM_ASM(
+        // Reduce allocated space at the very start.
+        var stream = FS.open("allocatetestfile", "w");
+        FS.allocate(stream, 0, 4);
+    );
+    stat("allocatetestfile", &allocateStat);
+    assert(allocateStat.st_size == 4);
+
+    EM_ASM(
+        var stream = FS.open("allocatetestfile", "w");
+        
+        var ex;
+        try {
+            // Attempt to allocate negative length.
+            FS.allocate(stream, 0, -1);
+        } catch (err) {
+            ex = err;
+        }
+        assert(ex.name === "ErrnoError" && ex.errno === 28 /* EINVAL */);
+    );
+
+    remove("allocatetestfile");
+}
+
 void test_fs_truncate() {
     EM_ASM(
         FS.writeFile('truncatetest', 'a=1\nb=2\n');
@@ -182,12 +222,11 @@ int main() {
         FS.mkdir('/dir2');
     );
 
-    struct stat s;
-    stat("/dir1", &s);
-    assert(S_ISDIR(s.st_mode));
-    stat("/dir2", &s);
-    assert(S_ISDIR(s.st_mode));
-
+    struct stat rmdirStat;
+    stat("/dir1", &rmdirStat);
+    assert(S_ISDIR(rmdirStat.st_mode));
+    stat("/dir2", &rmdirStat);
+    assert(S_ISDIR(rmdirStat.st_mode));
 
     EM_ASM(
         // Remove the multiple directories
@@ -255,15 +294,17 @@ int main() {
 
         FS.create("createtest", 0400); /* S_IRUSR */
     );
-    struct stat stats;
-    stat("mknodtest", &stats);
+    struct stat mknodStats;
+    stat("mknodtest", &mknodStats);
+
+    assert(S_ISREG(mknodStats.st_mode));
+    assert(mknodStats.st_mode & 0777);
 
-    assert(S_ISREG(stats.st_mode));
-    assert(stats.st_mode & 0777);
+    stat("createtest", &mknodStats);
+    assert(S_ISREG(mknodStats.st_mode));
+    assert(mknodStats.st_mode & 0400);
 
-    stat("createtest", &stats);
-    assert(S_ISREG(stats.st_mode));
-    assert(stats.st_mode & 0400);
+    test_fs_allocate();
 
     test_fs_truncate();